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Doepfer A-100

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This article is about the synthesizer. For information on the aircraft, see Aero A.100.
The Doepfer A-100 is an analog modular synthesizer system made by the German audio manufacturer Doepfer. It was first manufactured in 1995 and developed into a system of more than 80 modules plus enclosures and accessories. Modules for this system are still being manufactured today.

The A-100 modular synthesizer is compatible with modules from other manufacturers besides Doepfer. The A-100 is currently the most popular modular system in contemporary use. The Analog Solutions Concussor features many modules that are compatible with the A-100. These include bass drums, hi-hats, filters, LFO's, and many other modules. Other companies whose modules are compatible with the A-100 include the Electro-Acoustic Research Livewire and Plan B systems, Analog Systems, Metasonix, and Bananalogue, along with other manufacturers.

A-100 modules are designed to be mounted in a standard Eurorack 19-inch rack enclosure, each consuming 6 U of height and width varying according to the number of jacks, knobs, and other panel features. Modules are patched using standard mono miniature (3.5 mm) leads.

Notable users of the A-100 include Kraftwerk, Nine Inch Nails, and Human League.[link] The guitarist from the Red Hot Chili Peppers, John Frusciante, is an enthusiast of this synthesizer. He used it on the song The Will to Death. [link] Jean-Michel Jarre uses Doepfer gear as well.

Kraftwerk have been avid Doepfer enthusiasts since the early 1990s. Always being at the forefront of musical technology, Kraftwerk used an A-100 system for their 1998 world tour. Trent Reznor(of NIN fame)uses a Doepfer A-100 with modules from Analogue Solutions, Analog Systems, EMS, and Metasonix. The Doepfer Schaltwerk is his analog sequencer of choice(recently discontinued).

John Leckie, an engineer for New Order, utilized an A-100 box on the recent New Order Album : Waiting for the Sirens Call (2005). New Order's Blue Monday was one of the defining tracks of electronic music in the early 1980s. The A-100 has found favour amongst musicians known for pushing the boundaries of sound and electronic production technology. Keith Fullerton Whitman is also a Doepfer user.

Bon Harris, the programmer, engineer, and drummer for industrial band Nitzer Ebb used an A-100 when working on Smashing Pumpkins' album : Adore. Billy Corgan himself purchased this synthesizer for his use.

Not only used to make spacey sounds for rock music production or as a toy for synth-enthusiasts, the A-100 is also on the cutting edge of electronic dance music production. Canadian microhouse pioneer Akufen says about the A-100 : "It's analog,instructive,versatile,creative,fun, goodlooking,solid as a tank, affordable........ and addictive. DIETER YOU MADE IT,the modular is back in a very crafty and trustworthy way. Not to mention the good ol'way of purchasing the modules.No box,no book,no warranty,no stickers,no standard industrial presets......just a module wrapped in a paper bag with a bill in my pocket. Feel like a kid again! Maybe electronic musicians will feel the need of knowing,learning and exchanging again.Even my five year old daughter is getting a good kick out of it,she just flips on that vocoder. For professionals,hobbyists,modernists...... for everyone. BACK TO THE FUTURE! "

Following are listed the modules available for the A-100 as of May 2006. The modules are grouped by number and module type. This information can be found in more detail at www.doepfer.de. Information provided with permission from Doepfer.

Contents

Filters

A101-1 Vactrol Multitype Filter

This is a filter based on a vactrol, which is composed of a light depending resistor(LRD) and an LED. When the LED brightness is increased, the LRD resistance is decreased. Vactrols have the advantage of hangling high voltages without introducing distortion. The sound of this filter can be described as laid back and mellow. A disadvantage is that all vactrols behave a little bit differently. This module takes in 3 different audio sources into different points of the circuit, filtered by Low pass, band pass, and high pass, and are added together as the output.

Module A-101-1 is a special multitype filter based on an idea by Nyle A. Steiner (published in Electronic Design, issue 25, December 1974, page 96 ff). The circuit uses the standard non-inverting amplifier filter design. Different filter types (low pass / LP, band pass / BP, high pass / HP) are realized by injecting the audio signal into different points of the circuit and using a common output for all filter types. One may feed three different audio signals into the filter simultaneously. Each signal is filtered correspondingly (LP resp. BP resp. HP) and the sum of the three filtered signals appears at the output. Of course it is possible to feed the same signal to all three inputs. In this case one obtains different combinations of LP/BP/HP according to the settings of the three input attenuators for LP/BP/HP. Even a Notch filter is possible (not available in the original design). The filter inputs are normalled, i.e. the BP input is connected to the LP jack socket provided that no cable is plugged into the BP socket (same applies for HP/BP inputs). In contrast to the original circuit vactrols are used instead of diodes as variable resistors for frequency control of the filter. Due to the"crooked" response of vactrols the filter has not an exact frequency control standard (like V/Oct). The inevitable tolerances between different vactrols will lead to an individual sound of each module and individual resonance behaviour. Even the resonance control is realized with vactrols. Consequently this parameter is voltage controlled, too. Resonance can be increased up to self-oscillation. Resonance and consequently self-oscillation may vary with the filter frequency because of vactrol tolerances. A special feature of the module are the two audio outputs. Out 1 is the output of the original circuit. In the original circuit by Nyle A. Steiner the output level was distinctly dependent upon the resonance (higher resonance = higher output level). Out 2 compensates this behaviour by the usage of an additional vactrol that is connected in series to the vactrol that controls the resonance. This additional vactrol forms an attenuator (or simple VCA) that approximately compensates the level increase for higher resonance settings. Two LED displays show the current frequency and resonance setting. The LEDs are connected in series to the LEDs inside the vactrols and show consequently the LED illumination inside the vactrols.

A101-2 Vactrol Low Pass Gate

A-101-2 is a vactrol based combination of Low Pass filter (LP) and VCA and was inspired by the Buchla module 292. The term "Low Pass Gate" was created by Don Buchla and stands for a module that can be switched between low pass and VCA. The control (manually and via external CV) is responsible for frequency in the low pass mode and for loudness in the VCA mode. Additionally a combined mode LP+VCA is available. In this mode the sound becomes more dull as the loudness decreases. In contrast to the Buchla design the A-101-2 offers attenuators for both CV and audio input, a manual resonance control and two gate inputs to control the function of the module in addition to the manual toggle switch. In principle the A-101-2 is a 12 dB low pass filter that can be switched to VCA or a combination of Low Pass and VCA. The controlling elements for frequency (LP mode) resp. amplitude (VCA mode) are so-called vactrols. Vactrols are known for their smooth sound behaviour. For more general details about vactrols please look at the Vactrol Basics page. The Frequency (in the LP mode) resp. the Amplitude (in the VCA mode) is controlled manually (F/A) and by the 2 control inputs CV1 (without attenuator) and CV2 (with attenuator). The audio input is equipped with an attenuator to enable distortion too (above ~ position 5 distortion is obtained with standard A-100 audio levels, e.g. VCO). The resonance function "colors" to the sound and is adjustable all the way up to self-oscillation. Resonance and consequently self-oscillation may vary with the filter frequency because of vactrol tolerances. Due to the circuit the resonance has a little bit an influence on the audio level (increasing resonance = increasing audio level). To obtain the original Buchla sound the resonance control simply has to be set fully The function of the module is controlled by a manual switch. The left and right positions of the switch correspond to LP resp. VCA mode. In the middle position one obtains the combination of Low Pass and VCA. In this position it is also possible to control the function of the module by the two Gate inputs G1 and G2. The table printed at the front panel shows the connection between the gate levels (L = low, H = high) and the module function.

A101-3 Modular Vactrol Phase Filter

Module A-101-3 is a 12 stage phase shifter with vactrols as phase shifting elements. Vactrols are known for their smooth sound behaviour. For more general details about vactrols please look at the Vactrol Basics page.

In contrast to other phaser designs the A-101-3 is much more flexible and offering a lot of new features not available from other phasers on the market (as far as we know, please tell us if we are wrong). The main difference is that our design offers access to each of the 12 input and output stages leading to a lot of new filters that cannot be obtained in other ways. Especially the free patchable feedback loops (yes, not only one feedback loop is possible) between each of the 12 stages, the separate phase shift control for the stages 1-6 and 7-12, and the 2 polarizers intended to control the feedback loops lead to completely new filter types (a polarizer is a circuit that is able to generate positive and negative amplifications in the range -1...0...+1 with -1 = inversion, 0 = full attenuation, +1 = unchanged signal, for details concerning the polarizer function please look at the A-133 VC Polarizer or A-138c Polarizing Mixer module).

The module sketch and the frequency response curves below will help to explain the outstanding functions of the module:

Internally the module is made of 2 independent 6 stage phase shifters (1-6 reps. 7-12) with separate audio inputs (with attenuators), audio outputs (with mix control), and phase shift control units. The phase shift control units feature both manual and voltage controlled phase shifting (e.g. from a LFO, ADSR, Random Voltage, Theremin CV, Foot Controller CV ...). For each sub-module a phase shift display (LED) is available. The LED shows the illumination state of the 6 vactrols of the sub-module in question as it is connected in series with the internal vactrol LEDs.

Each of the 12 phase shift states is equipped with an audio output socket and feedback input socket to obtain full flexibility to create a multitude of different filters. The audio input signal and the output signals of stage 6 resp. stage 12 are mixed with 2 manual controls to obtain effects at two audio outputs (for normal phase shifting effect this is 50% input signal and 50% phase shifted signal). The two submodules are internally connected via normalized sockets so that two 6 stage phase shifters can be obtained without external patches. Audio output of stage 6 is normalized to audio input of stage 7 and CV input 1-6 is normalized to CV input 7-12. But due to the open structure of the module even other stages than stage 6 and stage 12 can be used as outputs to generate different sounds (simply patch the desired stage output to the normalized mix input socket).

For a better understanding of the outstanding features a table with frequency response graphs is added at the end of this document.

The first 12 frequency response curves show the behaviour of the module when stages 1...12 are used as outputs for the final mixer (no feedback, no additional patching). This is the standard phaser application with a different number of phase shift stages. The frequency response curves of the higher stages show the typical comb filters of a phaser. The notches move through the audio spectrum as the manual phase shift control is operated or a control voltage is applied (for a standard phase shifter this is normally the triangle or sine wave from a LFO). The number of notches increases with the number of stages: number of notches = integer of number of stages/2. Odd stage numbers lead to different behaviours in the higher and lower frequencies (low end: high pass behaviour, high end: passage). Even stage numbers show the same response in the higher and lower frequencies (passage for both). Stage 1 is nothing but a high pass filter, stage 2 is the standard notch filter.

The second 12 frequency response curves show the behaviour when an inverter is inserted between the stage output in question and the final mixer (one of the polarizers can be used for this job). The result is the inverse frequency response compared to the output without inverter: e.g. low pass for stage 1, band pass for stage 2. The resulting frequency response curve is simply obtained by vertical mirroring the first 12 curves.

Additional feedback colors the sound. The third 12 frequency response curves show the behaviour of the filters with one feedback loop. Feedback comes from the stage used as output back to stage 1 (e.g. if stage 11 is used, feedback from stage 11 to stage 1).

But it is not imperative to use the same stage for feedback and audio output. Groups 4, 5 and 6 of frequency response curves show the behaviour with different feedback loops. In group 4 the same output 12 is used for all graphs but but the feedback goes from stage 12, 11, 10, 9 ... and so on back to stage 1. Group 5 is nearly the same but output 6 is used for all graphs. In group 6 the output stage is the varying parameter and the feedback goes from stage 8 to 1 for all filters.

Last but not least the open structure of the module allows multiple feedback loops (e.g. stage 8 to 3 and stage 6 to 1 simultaneously) and even "forward" loops (e.g. from stage 5 to stage 9). In combination with polarizers additionally the feedback or the output polarity can be normal or inverted. This leads to a multitude of possible filter types. Some examples for multiple and forward loops are shown in the last section of the response curves. Pay attention that for some examples e.g. varying the feedback leads to "moving" peaks. By means of VCAs (A-130, A-131, A-132) or the voltage controlled polarizer A-133 the feedbacks can be voltage controlled.

A101-9 Universal Vactrol Module

No information was provided.

A-102 Diode Low Pass Filter

Module A-102 is a reproduction of the legendary low pass filter design that uses diodes in the filter stage as frequency controlling elements resulting in "strange" resonance behaviour and frequency response as resonance and frequency are not independent from another.

As for the rest the A-102 is identical to the A-120 Moog low pass filter resp. the A-103 (18dB TB303 Filter). I.e. the same controls, inputs and outputs. Only the filter sound is different.

A-103 18DB Low Pass 1

Module A-103 is a voltage controlled low pass filter with 18dB/octave slope. The circuit is based on a modified transistor ladder (Moog ladder) and is a reproduction of the legendary TB303 filter.

As for the rest the A-103 is identical to the A-120 Moog low pass filter (same controls, inputs/outputs) only the filter sound is different.

A-104 Trautonium Formant Filter

A-104 is a fourfold formant filter as used in the Mixtur Trautonium by Oskar Sala. It is made of four parallel resonance filters, each filter can be switched to low pass or band pass or off. Frequency, resonance and level are controlled for each filter separately (no voltage control). The frequency range for the filters is about 50Hz...5kHz. The filter audio inputs are very sensitive so that distortion may intentionally be used to create new sounds - if desired. The A-104 is a versatile module for sound modification. In the first place it is used for reproduction of resonances (e.g. the vocal-like effects known from the Trautonium). In combination with the subharmonic generator A-113, the Trautonium Manual A-198 and some other A-100 modules one obtains a Trautonium replica.

A-105 24 DB SSM Low Pass Filter

Module A-105 is another voltage-controlled low-pass filter with 24dB/octave slope. The A-105 is very similar to the A-122 that is made with a CEM chip. But in contrast to the A-122 the A-105 is made with the legendary SSM filter chip SSM2044. This chip was used e.g. in these synthesizers: Korg Polysix, Korg Mono/Poly, Fairlight II, PPG Wave 2.2 und 2.3, Emu SP-1200, Siel DK600, Siel Opera 6. The first Prophets used the SSM2040 - the precedessor of the 2044 - that generates a very similar sound. The special feature of the 4 pole low pass SSM2044 is the patented so-called "true open loop design that delivers a characteristic fat sound not available from other devices" (extract from SSM2044 data sheet). The module will feature voltage controlled resonance and a sensitve audio input to obtain distortion - if desired. Regarding to the functions, controls and in/outputs the module is identical to the 24dB low pass filter A-122 that is built around a CEM chip. But the sound, the resonance behaviour and the distortion behaviour are completely different for both modules.

A-106-1 Xtreme Lowpass/Hipass Filter

Module A-106-1 has it's origin in the experiments to built a MS20 filter clone. The famous original MS20 included two filters: a 12 dB lowpass and a 6dB high pass filter connected in series both with a very special design (the MS20 highpass if very often described as 12dB high pass, but this is not true). During research, a way was found to use the same circuit simultaneously as lowpass and highpass for 2 different audio signals (a bit similar to the A-101-1 Steiner Vactrol filter that has even different audio inputs available, but with the special MS20 circuit). For this two separate audio inputs for lowpass (LP) and highpass (HP) with separate level controls are available. The sockets are normalled, i.e. the signal applied to the LP input is available for the HP input too provided that no plug is inserted into the HP input socket. The level control of the HP input is realized as a polarized input. This means that the signal can be added with the same polarity (+ range) or opposite polarity (- range) compared to the LP input. This feature enables notch (+) and bandpass (-) filter functions too. With this module, these functions are available:

This design allows even some very special functions: It is e.g. possible to adjust the controls so that the LP signal does not distort but the HP share does (or the other way round) - alternatively with the same or opposite polarity compared to the LP signal. For this the LP level has to be set to a small value so that the signal does not distort. The HP level control has to be set to a higher value (in the + or - range) so that the HP share will distort.

The variety of controls allows a lot of functions that are not available for any other filter known.

During the A-106-1 development it was also found that it might be useful to add controls not available in the original MS20 filters. In the original circuit the filter output level is limited to about +/- 0.7V by two antiparallel diodes across the output/resonance amplifier. By chance we discovered that removing one or both diodes leads to noticeable different behaviour of the filter. Moreover we added two rotary controls CL+ and CL- to adjust the effect of each limiting diode (from original MS20 behaviour, i.e. fully active limiting diodes, to no limiting effect). The independent control for each diode allows asymmetrical limiting/amplification that causes a completely new and sometimes very strange behaviour. One of the main effects of the asymmetrical limiting is that in self-oscillation the filter does not generate a sine wave but short pulses if only one of the limiting diodes is activated. Another effect is that a higher output of the filter can be obtained (limited to about +/- 0.7V for the original MS20 circuit). In addition dirty noise effects appear at certain combinations of the control settings for resonance, CL+, CL- and input level. The controls CL+, CL-, Resonance, LP level and HP level have be looked at always in a common context: if the input levels are small the CL+ and CL- controls will have no effect as the signal does not distort at all. Increasing the resonance also increases the audio level and the CL+/CL- controls may now have an effect without changing the input level ! Same applies if the resonance control remains unchanged but the input level is increases. Now the CL+ or CL- control will have an effect as the level reaches the clipping thresholds. Increasing the audio level does also may suppress the resonance if distortion becomes extreme. The "teamwork" of the five controls is very complex and has to be learned by doing and hearing.

The audio inputs are very sensitive to allow even extreme distortion effects, much more than possible for the original MS20.

The module was also expanded by an insert option for the resonance feedback loop. This allows to insert other A-100 modules into the resonance circuit. The standard application is to insert a VCA for voltage controlled resonance. But even other modules - e.g. waveshaper, divider, phaser, distortion, PLL, wave multiplier, spring reverb, ring modulator, frequency shifter ony any other audio processing module - can be inserted to obtain sounds you have never heard before.

On top of this the module is equipped with two frequency CV inputs. One is carried out as a polarizer. This means that effect of the external CV (e.g. envelope from an ADSR A-140 or A-141) to the filter frequency is positive (+ range) or negative (- range). Especially when the filter is moved from LP to HP it might be useful to invert the polarity of the envelope CV. We also have to mention that the frequency response if far from 1V/oct but rather non-linear.

To obtain the filter section of the original MS20 two A-106-1 have to be patched in series (one in LP mode, the other in HP mode, both with CL+ and CL- set to zero).

It has to be pointed out that the A-106-1 is far away from being a "perfect" filter in an academic sense: The control scale is non-linear. With self-oscillation all sorts of waveforms except sine are generated. With high distortion and resonance settings a lot of roaring/rattling/noise or other unpredictible sounds may appear. High distortion/level may "kill" the resonance at certain settings. The filter has a significant control voltage feedthrough. The "bandpass" is not a real band pass as a considerable share of all frequencies passes through. The notch filter does attenuate only about 50% at the center frequency - and many more. But the A-106-1 has a lot of character - much more than any other filter of the A-100. It is a very strange and awesome filter - somehow exactly the contrast to the A-108, which is a very smooth, warm and predictable filter. The A-106-1 is definitely not the right choice for "moogish" and "civilized" sounds but for extreme, exceptional and experimental sounds - this is why we call the module "X-Filter" to avoid troubles with the Korg company who is the owner of the term "MS20". If you want to know more technical details please look at the A-101-1 technical details. In this document the basics of the A-101-1 (Steiner) and A-106-1 (MS20) filters are described.

Included options: For the HP input control can be chosen if the polarizer is active or if a normal attenuator is available. For some applications it might be useful to have the level controls of LP and LP work in the same way (e.g. to obtain the same level for both inputs). With a jumper on the pc board the type of HP level control can be chosen. The CL+ and CL- parameters are prepared to be controlled by external vactrols. Two pin headers are used to establish a connection to the universal vactrol module that is still under development. This will allow voltage control of the CL+ and CL- parameter.

Application ideas:

A-107 Multitype Morphing Filter

Module A-107 is a completely new voltage controlled filter that has available 36 filter types: different versions of low pass, high pass, band pass, notch, all pass and filters with new response curves that have no name up to now. The frequency response curves of the 36 filters available in the A-107 are shown in the graphics at the end of this page. The filters are organized in two groups of 18 filters each. The transition between different filter types within one group can be soft (morphing) or hard (switching).

The filter was inspired by the ERWIK Musikelektronik Multimode Filter, which is based on the filter used in the Oberheim Matrix 12 resp. Xpander (thanks to Jesper Erwik Johansson for his assistance and permission to use his idea in our A-107 module). The possibilities of the A-107 go far beyond these filter designs as a lot of new filter types are available and the transition between filters can be soft (morphing) or hard (switching) and the filters can be arranged in 64 different voltage controlled filter chains.

The transistion between the different filter types is controlled by two parameters:

For both parameters manual control, one CV input with attenuator and one CV input without attenuator are available.

The 36 filter types can be arranged in filter chains (resp. filter sequencer or filter orders) so that this sequence of filters is passed through while the control voltage changes from 0...+5V. Each chain consists of 32 steps. 64 filter chains can be programmed by the user and stored in the non-volatile memory of the module. The following controls are used to program the filter chains:

Additionally a "clocked" mode is available. This means that the steps of the currently selected filter chain are selected one after another. Each positive transition of the Clock signal calls up the next filter of the chain (jack socket marked Step Clock). A positive trigger at the Step Reset input (jack socket marked Step Reset) resets to the first filter of the current filter chain. This allows e.g. to switch between the filters of the currently selected filter chain in sync with a sequencer.

Of course the standard VCF controls are available: manual filter frequency control, one CV input with attenuator and one CV input without attenuator.

In addition voltage controlled resonance with manual control, CV input with attenuator and CV control without attenuator are available. For the filters of the first group (1...18) self-oscillation is possible, the filters of the second group (19...36) do not feature self-oscillation.

On top of it a final VCA is available (even with manual control, CV input with attenuator and CV input without attenuator).

The filter design is 100% analog (CEM filter chip). Only the morphing control and memory managing is carried out by a microcontroller.

A-108 6/12/24/48 db Low Pass Filter

Module A-108 is a completely new voltage-controlled low pass pass filter based on the well-known transistor ladder (Moog ladder). The module has internally an 8 stage low pass filter with different slopes available: 6, 12, 18, 24, 30, 36, 42 and 48 dB per octave. In addition it features an band pass output (i.e. band pass with transistor ladder). In the factory the 4 low pass outputs of the A-108 are internally connected to the filter stages 6, 12, 24 and 48dB. From our first A-108 audio tests this seems to be the best output combination as these outputs generate audible different sounds. E.g. the audible difference between the 48dB and 42dB or between 42dB and 36dB is very little. But if desired any of the filter stages can be connected to one of the outputs.

Remark: Only 4 output stages are available as this seems to be sufficient from our experiences. In the factory the out stages are connected to the filter stages with 6, 12, 24 and 48 dB slope. By changing the internal connections (jumpers or wires) each of the filter stages can be used but only four at a time. Even a multi-way switch could be used but from our results the factory setting (6/12/24/48dB) is the best combination for musical applications. From our experience it would e.g. make not much sense to have 30dB, 36dB, 42dB and 48dB available simultaneously - but if desired one could have this combination avaiable. More details below (after the frequency response pictures).

Resonance (Emphasis or Q ) can be adjusted manually right up to self-oscillation, in which case the filter will behave like a sine wave oscillator. The A-108 features an external feedback input that enables the insertion of additinal modules into the feedback path (e.g. VCA for voltage controlled resonance or phaser/frequency shifter for phase/frequency shifting effects). The socket is normalized and internally connected to the 48dB low pass output if no cable is inserted into the feedback socket.

The frequency can be adjusted manually, or by voltage control. Three CV inputs (CV1, CV2, CV3) are available. CV2 and CV3 are eqipped with attenuators.

The filter audio input is very sensitive so that distortion - if desired - is possible even with normal A-100 levels (e.g. VCO output). Self oscillation will break off at high distortion levels as the internal feedback signal is drown out by the distorted audio signal. This feature may intentionally be used to create new sounds.

In combination with the Voltage Controlled Mixer A-135 and the Morphing Controller A-144 a filter with voltage controlled slope can be realized (i.e. controlling the slope from 6dB to 48dB via CV).

A-109 Voltage Controlled Signal Processor

Module A-109 is a voltage controlled audio signal processor containing the following components:

The VCF is a standard 4 pole low pass filter with voltage controlled resonance. The filter has a so-called "constant amplitude versus resonance design", i.e. the peak-to-peak output level remains within 6dB when the output waveform rings from added resonance. Manual controls for frequency and resonance are available as well as 2 CV inputs for both (one with attenuator). The frequency range is about 5 Hz ... 20kHz, resonance ranges from 0dB up to self oscillation.

The main VCA has a combined exponential/linear control scale: exponential from about 0...+200mV (corresponding to about -100dB ... -20dB), linear from about 200mV...+5V (corresponding to -20dB...0dB). The "rounded" knee at the scale bottom allows an envelope to decay to zero with a natural exponential sound. Manual control for amplitude is available as well as 2 CV inputs (one with attenuator).

The gains of the panning VCAs are complementary, being equal and half of maximum at about +2.5V CV. The control scales are linear between about +1 and +3.5V CV, becoming logarithmic beyond these extremes. Manual control for panning is available as well as 2 CV inputs (one with attenuator).

The audio in/outputs of the module are normalized, e.g. the VCF output is fed into the VCA input privided that no jack plug is inserted to the VCA audio input socket.

The A-109 module is based on Doug Curtis' CEM3379 that was used in many Sequential Circuits™, Ensoniq™ and PPG™ synthesizers.

Sound Sources and Sound Modifiers

A-110 Standard VCO

Module A-110 is a voltage-controlled oscillator. This VCO's frequency range is about eight octaves. It can produce four waveforms simultaneously: square, sawtooth, triangle, and sine wave. The Frequency or pitch of the VCO is determined by the position of the octave (Range) switch and tuning (Tune) knob, and by the voltage present at the CV inputs. Frequency modulation (FM) of the VCO is therefore a possibility. Footage (the octave of the fundamental) is set by the Range control, and Fine tuning controlled by the Tune knob.

You can control the pulse width of the square wave either by hand, or by voltage control - Pulse Width Modulation or PWM.

A-111 High-End VCO

Module A-111 (VCO 2) is a voltage controlled oscillator. The VCO has a range of about 12 octaves, and produces four waveforms simultaneously: pulse (rectangle), sawtooth, triangle and sine waves. The VCO's frequency is determined by the position of the range switch, tune and fine tune controls, and the voltage at the two pitch CV inputs, CV 1 and CV 2. Footage (the octave of the fundamental) is set by the Range control, which has seven octave steps. The Tune control is used for coarse tuning, and the Fine control for fine tuning of the VCO pitch. The A-111 can be modulated by both exponential and linear FM (frequency modulation). You can control the pulse width of the square wave either by hand, or by voltage control - Pulse Width Modulation, or PWM for short.

The A-111 has inputs for Hard Sync and Soft Sync.

A-112 Sampler and Wavetable Oscillator

Module A-112 is the combination of a voltage controlled 8 Bit Sampler and a wavetable oscillator. On top of it the module is able to generate some special effects. A-112 was designed as an additional sound source with the typical sounds of the early 8 bit samplers and is not comparable with the modern polyphonic MIDI samplers available on the market.

Sampling mode: 8 bit audio resolution, 128kB memory in 2 banks 64kB each (equivalent to 2 seconds of sampling time for each bank with 32 kHz sampling rate), audio input with attenuator, overload display in record mode (gate LED), possibility of MIDI Dump to store sounds in a computer via MIDI, non volatile memory for the 2 samples in the module, manual tune control for adjustment of sampling rate for record and play, CV input (~ 1V/Oct), both manual tune and CV determine the sampling rate respectively the pitch (pitch range is 5 octaves), gate input (not a trigger: the sample starts at the positive edge of the gate signal and is played as long as gate is high or until the end of the sample is reached), manual Gate button, non filtered audio output (thus quantizing noise can be used as an element of the sound intentionally)

Wavetable mode: special appearance of the sampling mode when playing a sample, the audio input is now used as a second control voltage input for moving through the sample in 256 byte wide loops (wavetables). To achieve the typical wavetable oscillator sounds the sampling memory must contain corresponding wavetable data (normally loaded via MIDI dump). These data contain a set of wavetables with different harmonic content (e.g. a filter sweep) to get the typical wavetable sound while moving through the tables via CV2. But you may also use a "normal" sample and go through the sample with CV2 to obtain partially amazing sounds never heard before. You may use for example sampled speech and go with CV2 through the syllables or speech shreds to get really very extreme sounds.

Effects: Additionally the module offers - in a way free of charge - some effects like delay, reverse delay, pitch shiftinng or freeze. But it has to be pointed out that due to the 8 bit audio resolution these effects are not comparable to high quality effect units.

A-113 Subharmonic Generator

Module A-113 is a new sound source that derives from an incoming pulse signal four so-called subharmonics (German: Subharmonische). The term subharmonics was introduced by Oskar Sala in connection with his so-called Mixtur-Trautonium. A subharmonic means in this context a sawtooth wave (German: Kippschwinger) whose frequency is derived from a master frequency and the master frequency is an integer multiple in the range of 1...24 of the subharmonic - in other words: the master frequency is divided by an integer 1...24 to obtain the subharmonic. Pay attention that the output waveform of a subharmonic is sawtooth (as also used in the original Trautonium) and not sine. The term subharmonics is somewhat misleading. The master frequency comes e.g. from an A-110 or A-111 to the frequency input of the A-113. The frequency dividers of the 4 subharmonics is adjusted with up/down buttons as displayed with 2 character LED displays. The subharmonics are available as single outputs and as mix output with adjustable levels for the subharmonics.

Two gate type control inputs enable to select between 4 different mixtures, i.e. 4 different settings of the frequency dividers. In the original Trautonium these are controlled by foot switches to switch between 3 mixtures while playing (the original Trautonium has only 3 mixtures available but with the 2 gate inputs of the A-113 four different settings can be adressed).

Additionally the A-113 features a mixture memory with 50 presets. Each preset consists of 4 mixtures that can be selected with the gate inputs, each mixture contains the values of the 4 frequency dividers.

More detailed information about the Trautonium can be found on our internet site in the Trautonium project article. These additional Trautonium modules are available: Trautonium Manual A-198, Trautonium Filter A-104.

Inputs : master frequency (rectangle/pulse input), foot contr. 1 + 2 (gate 1+2)

Outputs: 4 single outputs, 1 mixture output

A-114 Dual Ring Modulator

Module A-114 contains two separate ring modulators. A ring modulator outputs the product (Multiplication X & Y) of the signals at inputs X and Y. It's similar to a VCA, but whereas a VCA only responds to positive voltages at the inputs (2-quadrant multiplication), the ring modulator responds to both positive and negative voltages (4-quadrant multiplication).

The ring modulator thus provides a refinement of amplitude modulation (AM). Ordinary amplitude modulation will output the original carrier frequency fC as well as the two side bands (fC - fM, fC + fM) for each of the spectral components of the carrier and modulation signals - but ring modulation cancels out the carrier frequencies, and just lets the side-bands pass to the output.

A ring modulator is used for the production of bell-like sounds, alien voices, or just to produce new timbres.

A-115 Audio Divider

Module A-115 is a four-way frequency divider. The frequency of a signal at the input is halved (half frequency = first sub-octave), quartered (1/4 frequency = second sub-octave), and so on. In this way, the DIVIDER produces four sub-octaves (F/2 down to F/16).

At the output, the A-115 produces a summed mix of the original and the four sub-octaves. There are attenuators to control the amount (ie. Amplitude) of the original signal and each of the sub-octaves.

Bear in mind that the sub-octaves output by the A-115 are all true square waves. At the output there are always four square waves and the original signal available.

A-116 Voltage Controlled Waveform Processor

Module A-116 provides voltage-controlled dynamic waveform modification of audio signals. It can produce new waveforms from the standard VCO shapes, and modulate these changes in real time. The signal first of all goes through an input amplifier, which can attenuate the signal as well as amplify it by up to a factor of 2.

After the input amplifier, the signal goes through two parallel processors: a clipping circuit, and an asymmetrical amplifier. The processed signals are added together and sent to the output.

Clipping-Level and Symmetry amounts are not just manually controllable, but can also be modulated by control voltages, to produce complex, constantly changing waveforms.

A-117 Digital Noise/ Random Clock / 808 Sound Source

Module A-117 (DNG) is a combination module, including a digital noise generator and an 808 source.

The digital noise generator uses random sequences of square waves (18 step shift register with multiple feedback), whose rate can go from random clicks to pure noise. The colour of the noise is very different from the analog noise produced by the A-118.

In addition to a manual setting, the rate can be controlled by an external clock - eg. VCO, LFO or MIDI clock.

The 808 Source aims to re-create the sort of multi-oscillator array that was used in Roland's TR-808 and TR-606 drum machines as the basis of the sound of the hi-hat, cymbals and cowbell. The cowbell mix uses two oscillators, and the cymbals mix six.

A-118 Noise/Random

Module A-118 is (as you might have guessed) a noise and random voltage generator. It produces three types of signal: white noise, colored noise, and random voltage.

White and colored noise can be used as audio sources, and also, in conjunction with a sample & hold module, as control voltages, and the random voltage is a useful source of voltage control, especially for its low frequency content.

The A-118 gives you the ability to mix the relative amounts of Red (low frequency component) and Blue noise (high frequency component) in the colored noise output.

There are knobs to control the rate of change and amplitude of the random voltage, and two LEDs indicate the state of the voltage at any one time.

A-119 External Input / Envelope Follower

Module A-119 (External Input / Envelope Follower) is designed to allow external audio signals to be integrated into the System A-100. It comprises a pre-amp, envelope follower, and comparator.

The pre-amp has two inputs: an unbalanced input for line level signals, with a gain factor of from 0 to 20, and a balanced input with a gain factor of from 0 to 500, for insertion of low level signals, for instance from a microphone or electric guitar.

The Envelope Follower reads the signal level of the input, and puts out a proportional voltage as an envelope at its own output.

The comparator generates a gate signal whenever the input goes above an adjustable trigger threshold.

Three LEDs help to keep track of overload, the envelope, and the gate signal.

Filters

A-120 24dB Low Pass Filter 1 (VCF 1)

Module A-120 is a voltage controlled low-pass filter, which filters out the higher parts of the sound spectrum, and lets lower frequencies pass through. The Cut-Off Frequency determines the point at which filtering takes effect. You can control this manually, or by voltage control (filter modulation, for instance by an LFO). Three CV inputs are available, and the sum of the voltages from these affects the filter cut-off.

VCF1 is a co-called "transistor ladder" design, with a cut-off slope of -24 dB/octave, as in various Moog synthesizers. That's what gives it its classic, legendary Moog sound.

Resonance (or Emphasis) is adjustable all the way up to self-oscillation - in which case the filter behaves like a sine wave oscillator.

A-121 Multimode Filter (VCF 2)

Module A-121 is a voltage-controlled multi-mode filter with a cut-off slope of -12 dB / octave.

Four simultaneous outputs are available, each with different characteristics: low-pass, band-pass, high-pass and notch (or band reject).

The cut-off frequency determines the point at which the respective filter effects appear. The frequency can be adjusted manually, or by voltage control (Filter modulation, for instance by an LFO or ADSR). Two CV inputs are available, whose control voltages are summed.

Resonance (Emphasis or Q ) can be adjusted manually, or by voltage control (voltage-controlled resonance / VCQ), right up to self-oscillation, in which case it will behave like a sine wave oscillator.

A-122 24dB Low Pass Filter 2 (VCF 3)

Module A-122 (VCF 3) is a voltage-controlled low-pass filter, which filters out the higher parts of the sound spectrum, and lets lower frequencies pass through.

The cut-off frequency determines the point at which filtering takes effect. You can control this manually, or by voltage control (filter modulation, for instance by an LFO). Two CV inputs are available.

The cut-off slope is -24 dB/octave. The circuitry uses a Curtis CEM 3320 chip, and is very similar to the classic Oberheim filter sound. Because of its different circuitry and controls, the A-122 has a considerably different sound to the A-120 'Moog-like' filter, especially in the way the resonance behaves.

Voltage controlled resonance: on the VCF 3, resonance can be controlled not just manually, but by voltages as well, right up to self-oscillation. In this case, the filter behaves like a sine wave oscillator.

A-123 24dB High Pass (VCF 4)

Module A-123 (VCF 4) is a voltage-controlled high-pass filter, which filters out the lower parts of the sound spectrum, and lets higher frequencies pass through.

The cut-off frequency determines the point at which filtering takes effect. You can control this manually, or by voltage control (filter modulation, for instance by an LFO). Two CV inputs are available.

The cut-off slope is -24 dB/octave. The circuitry uses a Curtis CEM 3320 chip.

Voltage controlled resonance: on the VCF 4, resonance can be controlled not just manually, but by voltages as well, right up to self-oscillation. In this case, the filter behaves like a sine wave oscillator.

A-124 VCF5/\"Wasp\" Filter

Module A-124 is a special 12dB multimode filter using the "strange" filter circuit of the "EDP Wasp" (an analog synthesizer with black/yellow case built end of the seventies, manufactured by the UK company "Electronic Dream Plant"). This design "abuses" digital inverters as analog operational amplifiers leading to distortions and other "dirty" effects that generate the specific sound of this filter. The filter is equipped with a band pass output and a combined low/notch/high pass output. For this output a control knob defines the relation between low and high pass signal. If both signals appear at the same level (i.e. middle position of the Mix knob) one obtains a notch filter. Otherwise the low or high pass signal predominates. The filter enables no self oscillation in contrast to all other VCFs of the A-100 system.

Inputs: Audio In, CV In (2x)

Outputs: Bandpass Out, Low/Highpass Mix-Out

Controls: Audio and CV attenuator, Frequency, Resonance, LP/HP Mix

A-125 Voltage Controlled Phase Shifter

Module A-125 (VC Phaser) is a voltage controlled phase shifter.

Phase shifting can be controlled either manually or by voltage control.

Other parameters which can be controlled are resonance (governing the depth of the comb filtering, and tonal color) and mix (the amount of the original signal which is added to the phase-shifted signal). The A-125 is used to generate the typical phaser sound ("jet sound"). Due to the voltage control feature not only the usual LFO-controlled phasings but even ADSR-, random-, sequencer- or S&H-controlled phasings are possible. In combination with the Shepard generator A-191 and several A-125 never ending barberpole phasing effects come true.

A-126 Voltage Controlled Frequency Shifter (VCFS)

100% pure analog frequency shifter (pitch shifter), frequency shift can be controlled manually and with CV control input (with attenuator) from about 50Hz to 5kHz

Outputs:

Audio Input with Gain control and overload control (LED)

A-127 VC Resonance Filter

Module A-127 is a triple resonance filter unit. It contains three separate voltage controlled band pass filters. Each filter has its own LFO (triangle waveform) with LED display and adjustable frequency and amplitude. Instead of the internal LFO an external control voltage may be used to control the filter frequency. In this case the external voltage is fed into the external CV jack (with integrated switch to turn off the LFO signal) and the amplitude control of the LFO affects the level of the external CV signal. Each filter is equipped with the following controls: LFO frequency, LFO/external CV amplitude, filter frequency, filter resonance and filter amplitude. In addition to the mix output for all three filters each filter has a separate audio output. The original audio signal can be added to the triple filter mix signal with a separate control. All of the 3 filters share a common audio input with attenuator. The filter audio inputs are very sensitive so that distortion may intentionally be used to create new sounds - if desired.

The frequency control range of the bandpass filters is about 40Hz...6kHz, the frequency range of the LFO's is about 0.02Hz...20Hz (= 1 min ... 1/20 sec per cycle).

Each of the three filters can used also as a 12dB low pass (with resonance control) instead of band pass. For this a jumper has to be changed on the filter board in question. In this case the module can be called no longer "resonance filter" but "triple low pass filter". It is also possible to modify only one or two of the filters to low pass.

The A-127 is a versatile module for sound modification. Here are some application samples:

A-128 : Fixed Filter Bank

Module A-128 (Fixed Filter Bank) is a filter bank, made up of 15 parallel band pass filters, all with fixed middle frequencies and bandwidth (50 Hz / 75Hz / 110Hz / 150Hz / 220Hz / 350Hz / 500Hz / 750Hz / 1.1kHz / 1.6kHz / 2.2kHz / 3.6kHz / 5.2kHz / 7.5kHz / 11 kHz).

Each band pass filter has its own amplitude control knob, with which that frequency band can be attenuated. The bandwidth of each of the filters is approximately half an octave.

The signal at the output of the A-128 contains a mix of all the filters, depending on the position of each one's amplitude control knob.

The filter bank's main job is to emphasise individual sections of the whole audio frequency range.

A-129 Vocoder System

This system is composed of 5 different modules that make up a complete vocoder. The voice signal is fed into the vocoder's analysis input (A-129/1). This signal is sent through a set of parallel filters with successive envelope followers that create a "signature" of the input signal, based on the frequency content and level of the frequency components. The signal to be processed (e.g. VCO or Noise) is fed into the synthesis input of the vocoder (A-129/2) and sent through an identical set of parallel filters with a separate VCA (voltage controlled amplifier) behind each filter. The envelope follower outputs of the analysis section are used to control the VCAs of the synthesis section. The filter signature created during the analysis of the human voice is used to filter the synthesized sound with a frequency responce similar to the voice. Consequently the output of the vocoder contains the synthesized sound modulated by the filter created by the voice. One hears a synthesized sound that pulses to the tempo of the voice with the tonal characteristics of the voice added to it: the synthesized signal "talks".

For most of the standard vocoders the control voltages generated by the analysis section (envelope follower outputs) are connected to the VCA control inputs of the synthesis section. For the modular vocoder A-129 the control voltage outputs of the analysis section A-129/1 and the control voltage inputs of the synthesis section are available as jack sockets. This enables the user to process the control voltages with other modules (e.g. the slew limiter/attenuator/offset generator (see A-129/3 and A-129/4) to obtain functions not possible with a non-modular vocoders. Another advantage of the modular concept is the possibility to exchange or shift frequency bands. And the modular vocoder could be "abused" in many ways, e.g. by controlling, modifying or creating the control voltages with other A-100 modules (e.g. LFOs, S&H, Random CV, Shepard voltages) or even to record the "vocoding" with CV-to-MIDI and MIDI-to-CV interfaces (e.g. A-192 and A-191).

A-129-1 Vocoder Analysis Section and A-129-2 Vocoder Analysis Section

The A-129 series of modules forms a modular vocoder. The basic components are an analysis section (A-129 /1) and a synthesis section (A-129 /2). As previously mentioned, the vocoder needs two input signals: a voice element which serves as the raw material for the tonal shaping, and is patched into the analysis section; and a carrier signal, which is patched via the instrument input into the synthesis section.

The speech signal is chopped up and analysed in the A-129/1 module, and then combined with the carrier signal in the A-129/2 synthesis section. As a result of this procedure, the carrier signal assumes the tonal character of the speech signal, but with its own pitch maintained.

Since the A-129 is a modular vocoder, and the connections between the analysis and synthesis section are external, using patch-leads, you can use this interface to patch in your choice of modules (eg. attenuator, slew limiter, CV-to-MIDI / MIDI-to-CV interfaces,, inverter, etc.). There's also the possibility of connecting the frequency bands of the analysis and synthesis sections arbitrarily, so that, for instance, a low frequency band in the speech signal can control a high frequency band in the carrier signal.

The A-129/2 synthesis section can also be used as a stand-alone voltage-controlled filter bank - or in combination with a MIDI-to-CV interface as a MIDI-controlled filter bank.

The A-129/1+2 both use 15 high quality narrow filters: 13 band pass filters, 1 low pass and 1 high pass filter:

A-129-3 Vocoder Slew Limiter

The Five-way VC slew limiter / offset generator / attenuators (A-129 /3) and Slew controllers (A-129/4) are particularly designed for this purpose. Module A-129 /3 includes 5-way Attenuators, 5-way Offset Generators, and a Slew Limiter (which works on all the voltages at the five CV inputs simultaneously). Using the A-129 /3 just on its own, two functions are available:

The Slew Limiter function is only available if the Slew Control Input of the module A-129/3 is controlled by the Slew Limiter Controller A-129/4 (see below).

For the maximum extension of the vocoder three modules A-129/3 are required as the A-129/3 contains only 5 units but the complete vocoder has 15 frequency bands. Usually, the A-129/3 is patched between the CV outputs of the analysis section A-129/1 and the CV inputs of the synthesis section A-129/2. You can also use module A-129 /3, particularly in combination with A-129/4, for other purposes. For example, using the A-129/2 synthesis section only, you can make a filterbank.

Module A-129/3 can also be used out of a vocoder to attenuate any signal in the A-100 and to add a fixed offset voltage (e.g. to expand the features of the dual low cost VCA A-132, the Quantizer A-156 or the Sampler A-112).

A-129-4 Slew-Limiter Controller

To use the Slew Limiter section of the 129 /3, you need to have module A-129 /4 (Slew Limiter Controller) as well. It has several dedicated functions, and gives you control over the following slew limiter functions:

This set of functions is operated by the Slew Limiter Controller, A-129/4. For this the Slew Control Outputs of the A-129/4 are connected to the Slew Control Inputs of up to three A-129/3.

A-129-5 Voiced/unvoiced detector

The Voiced / unvoiced detector (A-129/5) can recognise voiced and unvoiced sections in the speech signal, and switch the carrier signal accordingly. The incoming speech signal is processed through a pre-amplifier with adjustable gain and a treble boost unit. The treble boost improves the vocoder effect. The voiced/unvoiced recognition system controls a voltage controlled switch (like A-150) which is used to switch between the voiced and unvoiced carrier signal (e.g. VCO and Noise). Additionally the voiced/unvoiced information is available a a gate signal. A LED displays the unvoiced state.

VCA, Mixers, Modifier

A-130 : Voltage Controlled Amplifier(linear) and A-131 : Voltage Controlled Amplifier(exponential)

Modules A-130 and A-131 provide voltage-controlled amplification. For audio signals, you would normally use the exponential VCA (A-131), and for control voltages, the linear VCA (A-130). It doesn't always have to be that way, though.

The amount of amplification the VCAs provide is determined by the voltage at the CV input, and the position of the gain control, which sets the overall gain in the system.

The VCA has two audio inputs, each with an attenuator. They are amplified by an amount determined by the combination of the gain and the two CV controls.

A-132 : Dual Voltage Controlled Amplifier

Module A-132 (Dual Low Cost VCA) contains two voltage controlled amplifiers, with a linear response most suited to regulating the level of control voltages (ADSR amount, level of vibrato effect, etc.).

In non-critical situations, though, its VCAs can be used to control audio signals.

Amplification is governed by the sum of the voltages patched into the two CV inputs.

A-133 : Dual Voltage Controlled Polarizer

A-133 is a special dual voltage controlled amplifier that enables both positive and negative amplifications. Negative amplification means in this context that the signal is inverted. The main application of the module is the processing of control voltages, e.g. ADSR or LFO. The amplification range is about -2.5....0....+2.5 (other amplification ranges for small additional charges, e.g. -1...+1 or -5...+5). Amplification can be adjusted manually (Man control) and by an external control voltage with attenuator (CV). The present amplification is displayed with two LEDs: one for positive and one for negative amplifications (not a signal display but amplification diplay, similar to A-134).

Another module with polarizing function is the Polarizing Mixer A-138c

A-134 : Voltage Controlled Panning

A-134 is a voltage controlled panning module. The module contains 2 linear VCAs (A-130 type with CEM3381). VCA2 works in the opposite direction of VCA1 i.e. the more VCA1's loudness increases the more VCA2's loudness decreases. The panning is adjusted with a control knob (manual control) and by 2 external control voltages, one equipped with an attenuator. Suitable CV sources are e.g. LFOs (A-145, A-146, A-147), envelope signals (A-140, A-141, A-142, A-119), random (A-118), Theremin (A-178) or a voltage coming from an MIDI-to-CV-Interface (A-190, A-191). The panning is displayed with 2 LEDs.

A-134 has an audio input with attenuator for each VCA. If the audio input of VCA2 is not used the audio input of VCA1 is connected with audio in of VCA 2. The module has three audio outputs: VCA1, VCA2 and a mix output providing the combined signal of both VCA's.

A-134 enables voltage controlled stereophonic panning effects (one audio signal distributed to 2 outputs), monophonic panning effects (2 audio inputs mixed to one audio output with voltage controlled loudness proportion) and combinations of both effects.

A-135 : Voltage Controlled Mixer

Module A-135 is a quad voltage controlled mixer. It is made of 4 independent linear VCA's. The VCA outputs are mixed to a common output. For each VCA the following inputs and controls are available: audio input with attenuator, control voltage input with attenuator, gain (pre-amplification). The VCA's are realized with high-quality CEM VCA's (CEM3381).

Applications: voltage controlled mixing of up to 4 audio signals with separate control voltages (e.g. delivered by LFO's, ADSR's, Random, Shepard generator, MIDI-to-CV interface or other control voltage sources). In connection with the Morphing-Controller A-144 the soft fade-over of 4 audio signals with only one control voltage is possible.

A-136 : Distortion / Waveshaper

Module A-135 is a distortion and waveshaping module with extensive control possibilities. The incoming audio or cv signal is internally divided into 3 sections:

Different settings of 5 distortion/waveshaping parameters enable a lot of very complex and extreme waveform modifications. The range of modifications reaches from simple soft or hard clipping to completely altered waveforms where the original signal is no longer recognizable.

Applications: audio distortion (especially in combination with filters very interesting), waveform modification for audio signals as well as for control voltages (LFO, ADSR, random etc.).

A-137 : Wave Multiplier

A-137 is a voltage controlled Wave Multiplier. The basic idea of a wave multiplier is to multiply the waveform of an incoming signal (e.g. triangle/saw/sine from a VCO) within one period of the waveform. This leads to additional harmonics of the incoming signal. The period and consequently the pitch of the signals remains unchanged (in contrast to frequency multiplication e.g. with the PLL module A-196). The A-137 works as a kind of "inverse low pass filter", i.e. it adds a lot of harmonics to a signal that contains none or only a few harmonics (e.g. sine or triangle waveform). In contrast to that a low pass filter (e.g. A-120) removes harmonics from a signal that contains a lot of harmonics (e.g. saw or rectangle waveform). Consequently the best results are obtained in combination with input signals poor in harmonics (e.g. sine or triangle). The A-137 can be used with signals rich in harmonics too (e.g. saw) but the effect is not as remarkable as for triangle or sine waves. For rectangle signals none or only little effects are obtained.

The A-137 is a very sophisticated wave multiplier that offers much more features, more controls and more waveform manipulations than other wave multipliers available so far. In addition all parameters are both manually adjusted and controlled by external voltages.

A-138-a A-138-b : Mixer

Module A-138 is a four channel mixer, which can be used with either control voltages or audio signals. Each of the four inputs has an attenuator, and there's a master attenuator, so that the mixer can be used at the end of the audio chain - ie. it can be used to interface directly with an external mixer, amplifier, etc.

The module can be supplied in two versions:

A-138 a: potentiometers with linear response, so especially suitable for control voltage mixing.

A-138 b: potentiometers with logarithmic response, so especially suitable for audio signal mixing.

A-139 : Headphone Amplifier

This contains a 2 channel headphone amplifier, 2 audio inputs with level controls, master level control, and two headphone outputs.

5 - Modulation Sources

A-140 : ADSR Envelope Generator

Module A-140 is an envelope generator, and, since it puts out control voltages, counts as one of the modulation devices in a modular system. As soon as the gate input receives sufficient voltage, the ADSR generates a variable voltage, changing in time, called an envelope. This varying voltage is output in normal (positive) and inverted form, and can be used, eg., for voltage controlled modulation of a VCO, VCF, or VCA, or for processing other modules' inputs and outputs.

The shape of the envelope is governed by four parameters: Attack, Decay, Sustain and Release.

The envelope is started (triggered) by a gate signal either from the INT.GATE voltage on the system bus, or, if a signal is put into it, from the gate input socket.

The envelope can also be re-triggered, ie. start from scratch again, each time a trigger signal is sensed at the Retrig. input socket, when the gate is still open.

In combination with the Comparator module A-167 a free-running "ADSR-LFO" can be realized.

Related modules are the 4-fold ADSR A-143-2, the voltage controlled ADSR A-141 and the voltage controlled Decay/Gate module A-142.

A-141 : Voltage Controlled Envelope Generator VCADSR

Module A-141 (VCADSR) is a voltage controlled envelope generator - the voltage controlled version of the A-140. Whenever a gate signal is sensed at the VCADSR's gate input, an adjustable sequence of voltages is triggered - the envelope. You can then use these envelopes to modulate a VCO, VCF and/or VCA, and alter the input and output voltages of all sorts of modules.

The shape of the envelope is governed by four parameters: Attack, Decay, Sustain and Release. On the A-141, these parameters can be controlled by hand, or by voltage control, via the dedicated CV inputs (each with an attenuator).

The A-141 VCADSR also has a retrigger facility: while the gate is open, a trigger pulse received at the retrigger socket will re-start the envelope from the beginning of its attack phase.

A-142 : Voltage Controlled Decay/Gate

Module A-142 is a voltage controlled envelope generator. The only time parameter is decay (like TB303). Decay may be adjustes manual and via voltage control input (with attenuator). The envelope output is displayed with LED control. Additionally from the envelope signal a Gate signal and an inverse Gate signal with adjustable threshold is derived. LED control for Gate output. Thus one obtains a voltage controlled Gate additionally or alternatively to the envelope signal with voltage controlled duration.

Typical applications: dynamic control of decay e.g. in combination with the Analog/Trigger Sequencer A-155, voltage controlled trigger delay functions (like A-162, but voltage controlled).

A-143-1 : Complex Envelope Generator / Quad AD-Generator / Quad LFO

Overview: Module A-143-1 is a complex envelope generator that consists of Attack/Decay generators. For the complex envelope generator the four units are daisy-chained, i.e. the preceding unit triggers the following unit. The four units can be used even as four separate AD generators (switch position AD) or AD-type LFOs (switch position ).

Details: Module A-143-1 contains four separate attack/decay type envelope generators. Each unit can be switched into a free running mode (LFO mode). The LFO mode differs in several points from a regular LFO (like A-145, A-146 or A-147): The slopes are exponential - in contrast to linear slopes of a normal LFO, and the frequency is defined by both controls. The attack control defines the time of the rising slope, the decay control the falling slope.

Each unit has available a comparator that compares the AD output voltage with a manually adjustable threshold and switches the corresponding comparator output (Cp 1...4) to "high" as soon as the AD output voltage goes in the decay phase below this value. The comparator output is normalled to the trigger input of the next stage via the switching contact of the trigger input socket. Consequently the first unit triggers the second, the second triggers the third and so on.

Each AD generator is equipped with a Polarizer (look at the Voltage Controlled Polarizer A-133 concerning details about the polarizer function) and a mixer that adds up all polarizer outputs. This allows to add up all AD/LFO output signals inverting or non-inverting with adjustable level to the mix output. Additionally a single output (Env 1...4) is available for each unit.

If the trigger input of unit 1 is controlled by a normal gate signal (e.g. from a keyboard resp. MIDI-to-CV/Gate interface) one obtains a very complex envelope signal at the mix output. The signal contains 8 segments controlled by Attack 1, Decay 1, Attack 2, Decay 2, Attack 3, Decay 3, Attack 4 and Decay 4. The transition between the stages (i.e. when the following AD generator is triggered) is controlled by threshold knob. The positive or negative contribution of each unit to the mix signal is adjusted with the Mixing Polarizer control. If the trigger input of unit 1 is controlled by the comparator output of unit 4 one obtains a 8 stage LFO.

The single AD outputs can be used to control VCAs or VCFs that open one after another corresponding to the AD signals (a little bit similar to the Shepard generator A-191).

The default-connection between the four units (CPn = Trig.n+1) can be interrupted by patching cables into the trigger inputs. Consequently the four units can be used as separate AD generators or LFOs. In any case the mix signal is available (e.g. mix of four AD generators or LFOs with adjustable level and sign).

In the LFO mode the comparator output serves as LFO rectangle output with adjustable pulse width (= threshold control).

Each unit is equipped with a separate LED display for envelop and comparator output.

A-143-2 : Quad ADSR

Module A-143-2 is a four-fold ADSR type envelope generator. Other modules of this series are the Complex Envelope Generator A-143-1 (Quad AD) and the Quad LFO A-143-3.
The module contains 4 independent ADSR-type envelope generators. Each sub-module has available the controls Attack, Decay, Sustain and Release. The three-position Range switch allows to select the desired time range (low - high - medium). The adjustable envelope time ranges from several minutes to less than 100 microseconds. On top of this each sub-module is equipped with three digital outputs (high/low): "End of Attack (EOA)", "End of Decay (EOD)" and "End of Release (EOR)". As soon as the criterion is valid (e.g. end of decay state) the corresponding digital outputs turns to "high". These outputs can be used e.g. to daisy-chain several ADSR sub-modules. For this the digital output in question (EOA, EOD or EOR) has to be connected to the Gate input of the following ADSR. Even automatically running envelopes (pseudo LFOs) or so-called "quadrature envelopes" with cyclical modulations of several ring-shaped, daisy-chained ADSRs are possible. To obtain a pseudo LFO simply the EOD or EOR output has to be connected to the Gate input of the same ADSR.

In addition to the obligatory Gate (G) input for envelope generators each sub-module has available a Retrigger (Rt) input. The retrigger turns the direction to "upward" if the envelope has already reached the decay state while the retrigger pulse occurs. If the envelope is still in the attack phase the retrigger input has no meaning. This a different behaviour from A-140 and A-141 !

All Gate inputs are normalled from top to bottom, i.e. the Gate input of the above sub-module is connected to the switching contact of the succeeding module. Thus only one Gate signal can be used to trigger all four sub-modules. But even other types of normalling are possible if desired (e.g. EOD or EOR of the above ADSR to the Gate input of the succeeding sub-module).

The envelope outputs are displayed with LEDs.

A-143-3 : Quad LFO

Module A-143-3 is a low-cost four-fold modulation oscillator, often called LFO (low frequency oscillator). Like the other modules of the A-143 series (A-143-1 and A-143-2) not a very "exciting" module, just a bread-and-butter device and a simple demon for work. The module contains four simple LFOs. Each LFO is equipped with three waveform outputs: triangle, rectangle and sawtooth. The frequency of the sawtooth output is twice the frequency of the other outputs. A three-way switch is used to select one of three frequency ranges mid-low-high, spanning from about two cycles per minute at the lowest, to moderate audio frequency at the highest (about 5 kHz).

A-144 : Morphing Controller

Module A-144 is a control voltage modifier that is used in combination with the voltage controlled mixer A-135 in the first place. From a linear increasing voltage at the input the module derives four displaced triangle output voltages. When these 4 outputs are connected to the four control voltage inputs of the A-135 one obtains a fading over of the four A-135 audio inputs ("morphing"). The Morphing can be controlled manual and modulated with an external control voltage (e.g. from LFO, ADSR, Random, MIDI-to-CV, Theremin, Light-to-CV, analog sequencer) with attenuator.

Applications: voltage controlled morphing of 4 audio signals in combination with A-135, e.g. morphing between the 4 waveform outputs of an VCA (sawtooth/ rectangle/ triangle/ sine) or the 4 filter outputs of the multimode filter A-121 (lowpass/ bandpass/ highpass/ notch) or the 4 filter outputs of the A-105 (6/12/18/24dB) to obtain a filter with voltage controlled slope

A-145 : LFO

Module A-145 is a low frequency oscillator, which produces cyclical control voltages in a very wide range of frequencies. Five waveforms are available: sawtooth, inverted sawtooth, triangle, sine and square wave.

The LFO can be used as a modulation source for any number of modules - for instance modulating the pulse width or frequency of a VCO, modulation of the cut-off frequency of a VCF, or amplitude modulation with a VCA.

A three-way switch lets you select three frequency ranges, spanning from one cycle every several minutes at the lowest, to audio frequency at the highest.

The LFO signal can also be synchronised, via the reset input.

A-146 : LFO 2

Module A-146 (LFO 2) is a Low Frequency Oscillator, which produces periodic control voltages over a wide range of frequencies.

The LFO can be used as a modulation source for a series of modules (for instance pulse width and/or frequency modulation of a VCO, modulation of a VCF cut-off frequency, amplitude modulation with a VCA).

Three outputs are available, with different waveforms: sawtooth / triangle; square wave, and positive-voltage square wave.

The waveform is continuously adjustable from rising sawtooth, through triangle to falling sawtooth. The same control affects the pulse width of the square wave.

A three-way switch can select one of three frequency ranges, spanning from one cycle every few minutes, at the lowest, up to audio frequency at the highest.

A-147 : Voltage Controlled Low Frequency Oscillator VCLFO

Module A-147 (VCLFO) is a voltage controlled low frequency oscillator, which can produce cyclical control voltages over a frequency range of about 50Hz to 1 minute periode time (i.e. about 0.015 Hz). The VCLFO can be patched as a modulation source similar to the other LFOs A-145 and A-146 for a wide range of modules (for instance, modulation of VCO pulse-width or frequency, VCF cut-off frequency, VCA amplitude modulation) and as a provider of repetitive or clock voltages (for instance to drive the A-161 clock sequencer). In contrast to A-145 and A-146 the frequency of the A-147 is voltage controlled.

A-148 : Dual Sample&hold

Module A-148 (Dual S&H) has two identical sample & hold modules, designed to produce 'staircase' voltages. The signal present at the sample input is sampled at a rate set by the signal at the trigger input, and held at that voltage at the S&H output.

The exact shape of the staircase depends on the sort of waveform at the sample input: NOISE or RANDOM signals produce random patterns; an LFO produces rising or falling staircase patterns.

A-149-1 : Quantized/Stored Random Voltages

Module A-149-1 is the first module of the A-149-x range. In this group we present by popular request several functions of Don Buchla's "Source of Uncertainty 265/266" (SOU) modules that cannot be realized with existing A-100 modules. Many functions of Buchla's 265 and 266 SOU can be realized with existing A-100 modules. For details please refer to A-100 patch examples.

Module A-149-1 has available four different analog random control voltages that are generated in different ways.

The "Quantized Random Voltages" section has available 2 CV outputs: "N+1 states" and "2N states". N is an integer number in the range 1...6 that can be adjusted with the manual control (Man N) and an external control voltage CVN with attenuator. Whenever the rising edge of the input clock signal (Clk In) appears a new random voltage is generated at the N+1 resp. 2N output. The N+1 output is capable to generate N+1 different voltage levels (or states), the 2N output up to 2N different states. If for example N is set to 4 the N+1 output generates up to 5, the 2N output 16 different states. The voltage steps of the 2N output are adjusted to 1/12 V in the factory. Consequently exact semitones can be obtained in combination with a VCO. The voltage steps of the n+1 output are adjusted to 1.0 V in the factory corresponding to octave intervals in combination with a VCO. For each output a trimming potentiometer is available on the pc board that enables the user to select other voltage steps for the output in question.

Even the "Stored Random Voltages" section has 2 stepped CV outputs available: one with even voltage distribution of the max. 256 output states and second one with adjustable voltage distribution probability. The distribution probability is adjusted by a manual control (Man D) and an external control voltage CVD with attenuator. With the control set fully counterclockwise most of the random voltages will be low magnitude but even medium and high magnitude voltages may appear but with smaller probability. As the control is turned to the right (or a positive control voltage appears at the CVD input) the distribution moves through medium to high magnitude voltage probability. The symbol at the lower jack socket shows this coherence graphically. The voltage range is 0...+5V for both outputs of the "Stored Random Voltages" section. For each output a trimming potentiometer is available on the pc board that enables the user to select another voltage range for the output in question.

The A-149-1 can be extended by 8 random digital voltages with the A-149-2 Digital Random Voltages module.

Technical details: If you are interested in technical details here is some information. All random voltages are derived from digital pseudo random generators that work with shift registers and digital feedback via exor gates (the same principle as used in the Digital Noise module A-117). The digital output voltages of the shift registers are added up with resistors to obtain variable stepped analog voltages. For the N+1 output all resistors have the same value, the 2N output uses resistors in ratios of 1:2:4:8:16:32. Consequently the N+1 output has less different states available than the 2N output. In addition the digital shift register outputs are gated dependent on the current N voltage (sum of manual control + external CV) by which the number of possible states can be reduced. In contrast to the A-117 the shift registers are not clocked by an internal oscillator but by the external clock input Clk In.

The generation of the "Stored Random Voltages" is similar but with different resistor values and more shift register outputs. In addition the random voltage is processed by a non-linear clipping unit with adjustable offset that allows to modify the distribution probability of the voltage levels appearing at the lower output.

Even though the module is intended to generate slowly varying control voltages clock frequencies up to moderate audio range (about 2 kHz) can be processed.

A-192-2 : Digital Random Voltages

A-149-2 is an extension module for A-149-1. It makes available 8 digital random voltages (i.e. only low/high states like a gate signal). The outputs are controlled by the "Quantized Random Voltages" section of the assigned A-149-1 and correspond to the 8 digital outputs of the shift register that is used to generate the Quantized Random Voltages (for detailes please refer to the A-149-1 description). As the alteration of the A-149-2 outputs is clock controlled by the Clk In of the "Quantized Random Voltages" section of the A-149-1 the A-149-2 can be used to create random rhythmical sequences.

The A-149-2 requires the A-149-1 and has to be mounted directly to the left or right of the A-149-1 as an internal ribbon cable connection has to be established between A-149-1 and A-149-2.

6 - Switches and Sequencers

A-150 : Dual Voltage Controlled Switch

Module A-150 (Dual VCS) contains two separate voltage-controlled switches.

Each switch has a control voltage input, a common Out / Input, and two In / Outputs. The switches are bi-directional: they can work in both directions, so can connect one input to either of two outputs, or either of two inputs to one output. Voltages in the range -8V...+8V at the O/I resp. I/O sockets can be processed by the module.

A-151 : Quad Sequential Switch

Module A-151 (Quad Sequential Switch) is like an electronic four-position rotary switch.

It includes trigger and reset inputs, four in / outputs, and a common out / input. Each time a pulse is received at the trigger input socket, the common out / input is connected to the next in / output. After the fourth in / output, the next trigger makes it step back to the first again, and so on. A positive pulse at the reset input switches the out / input immediately back to the first in / output (see Fig. 1). Voltages in the range -8V...+8V at the O/I resp. I/O sockets can be processed by the module.

Four LEDs indicate the active in / output (ie. the on that is connected to the out / input at any particular time).

A-152 : Voltage Addressed Track&Hold / Switch (Multiplexer) / Digital Outputs

Module A152 is a very useful switching and T&H module. It combines a voltage addressed 1-to-8 multiplexer and 8 fold T&H. The active in/output is displayed by a LED. The digital output of the currently addressed step outputs "high". The remaining digital outputs are low.

Instead of voltage control even clock/reset controlled addressing of the active step is possible. The rising edge of each clock signal causes an advance to the next state. The rising edge of the reset signal resets to step 1.

Basis principles: The sum of the voltages coming from the manual Address control and the CV input define the currently addressed step of the 3 sub-devices. If the module is controlled by clock and reset the control voltage has to remain unchanged as the CV control has priority over the clock/reset control (e.g. simply turn the CV control fully counterclockwise and do not touch the Address control knob).

Sub-device #1 is the bidirectional 8-fold multiplexer (kind of an electronical 8-fold rotary switch). Bidirectional means that it works into both directions like a mechanical rotary switch: the common socket may work as an output that is connected to one of the 8 inputs that are e.g. connected to modulation or audio sources. But the common socket may even function as input. In this case the signal applied to the common socket is output to the currently addressed single socket. The voltage range of the in/outputs to be switched is the full A-100 voltage range -12V....+12V. All A-100 signals can be switched without any restrictions.

Sub-device #2 is the addressed 8-fold T&H. The signal at the common T&H input is connected to the addressed T&H output. As soon as a new output is addressed the last voltage is stored at the output (Track&Hold function). The T&H section of the A-152 allows the emulation of the "toggling T&H" function of the Buchla module 266 "Source of Uncertainty". Only the first two T&H outputs of the A-152 are required for this application.

Sub-device #3 is the digital output section. The digital output of the currently addressed turns to "high". All other digital outputs are low. The digital outputs can be used to trigger e.g. envelope generators or to control the reset input in the clocked mode to reduce the number of addressed stages.

A-154 : Enhanced Sequential Controller

Module A-154 is a supplement to the A-155 Analog/Trigger Sequencer module. It offers a lot of new features that are not available in the basic control unit of the A-155. The A-154 is used to replace the control unit of one or two A-155, i.e. the section marked "Control" with Start / Stop / Step / Reset buttons and inputs in the upper left corner of the A-155 front panel. If the A-154 is used to control the A-155 the control section of the A-155 is put out of action.

These are the features of the A-154:

Remark: With the One-Shot modes the A-155/A-154 combination can be used e.g. as a complex envelope generator. The Gate resp. Trigger signal is applied to the Start input of the A-154. One analog row determines the levels of the envelope. The second analog row can be used to adjust the time length for each step. The Gate row can be used to select between smooth (Glide = on) or hard (Glide = off) transition between succeeding levels. For the One-Shot version of Random the sequence continues until accidentially the last step is addressed. Then the sequence stops. The combination of One-Shot and CV Addressed Step Selection is not available as it does not make sense.

Installation of the A-154: The 10 pin ribbon cable, that was used to connect the A-155 control section with the rest of the A-155 module has to be removed and plugged to the new A-154 sequencer controller. Therefore the A-154 has to be mounted on the right side of the A-155. In case that two A-155 have to be controlled the A-155 have to be mounted one on top of the other and the A-154 on the right side of the upper or lower A-155. Attention ! In case of two A-155 the second A-155 cannot be controlled by its "old" control unit. In this case both A-155 are controlled by the A-154 or the "old" control unit of the first A-155 (depending upon the position of the A-154 master switch).

A-155 : Analog/Trigger Sequencer

Analog and Trigger Sequencer, 2 rows of 8 steps with knobs and 2 rows of 8 steps switches

Features of the analog rows (knobs):

Features of the trigger rows (switches):

Control inputs and buttons:

Step and Reset are compatible to the MIDI interface A-190, i.e. in combination with the A-190 the A-155 may be synchronized via MIDI. The quantizing module A-156 can be used to quantize the infinite analog voltages coming from A-155 into discrete semitone steps (multiples of 1/12V). Without MIDI interface e.g. a LFO rectangle output can be used to define the tempo of the sequence.

The sequencer controller A-154 adds a lot of new functions to the A-155 (e.g. voltage controlled addressing, forward/backward/pendulum/random mode, voltage control of first and last step, voltage controlled clock and gate length, step skipping, combination of several A-155 in parallel/serial mode and many more).

A-156 : Dual Quantizer

Module A-156 is a Dual Control Voltage Quantizer. A quantizer converts a continuous control voltage in the range 0...10V into a stepped output voltage in the same voltage range (i.e. only certain voltages occur). Normally 1/12 V steps are used to obtain semitone steps. Quantizer 2 of the A-156 allows has more sophisticated quantizing modes like major scale (i.e. only voltages corresponding to the major scale), minor scale, major chord, minor chord, fundamental+fifth and addition of seventh or sixth when chords are selected. Only those voltages appear at the CV output which comply with the selection rule (e.g. minor chord with seventh). The mode setting of quantizer 2 is done with 3 switches (1-0-1 type with middle position). Quantizer 1 is working always in the semitone mode.

For each quantizer the following in/outputs are available:

On top of that the A-156 is provided with a common transpose CV input having an additive effect on both quantizers. This input is quantized in semitone steps. A typical application is the transposition of a sequence generated by the A-155 by a second control voltage (e.g. coming from the MIDI-CV interface A-190).

7 - Clock, Gate, and Digital Modules

A-160 : Clock/Trigger Divider

Module A-160 is a frequency divider for clock/trigger/gate signals, designed to be a source of lower frequencies, particularly for rhythm uses. The Trigger input will take clock signals from, eg., an LFO, MIDI sync, or the gate from a MIDI-CV interface.

At the outputs, you have access to the sub-divided clock signals, from half the clock frequency down to 1/64.

The A-160 also has a reset input. Whenever a reset signal is sensed, all outputs are set to zero, until the reset voltage disappears.

The Clock Divider can be used in combination with the A-161 Clock Sequencer to produce stepped sequences with a length of from one to eight events.

A-161 : Clock/Trigger Sequencer

Module A-161 is an eight-step Clock Sequencer which is internally connected to the Clock Divider (A-160). Eight outputs are sequentially switched by the clock signals from the A-160 (see Fig. 1) and can act, for instance, as sequential rhythmic triggers for an envelope. The reset on the A-160 also works on the A-161 (instant return to Step 1). In combination with a mixer (A-138) short analog sequences can be generated. Our MIDI-Analog-Sequencer MAQ16/3 is suitable for MIDI-controlled analog sequences up to 48 steps. A "real" analog sequencer with 8 steps is the A-155.

A-162 : Dual Trigger Delay

Module A-162 contains two separate delay circuits for trigger signals. This module makes it possible to delay the onset of a trigger pulse, and also change its length.

On each of the trigger delays, two controls can alter the onset time and duration of triggers, from about 0,01 up to round about ten seconds. A control LED indicates the onset and duration of the new trigger.

A voltage controlled version of a trigger delay can be realized with the module A-142 Voltage Controlled Decay/Gate.

A-163 : Voltage Controlled Frequency Divider

Module A-163 is a voltage controlled audio frequency divider. The frequency of the input signal (preferably the rectangle output of a VCO) is divided by an integer factor N (N = 1, 2, 3, 4 ... up to about 20). N can be adjusted manually and modulated with an external control voltage (e.g. from LFO, ADSR, Random, MIDI-to-CV, Theremin, Light-to-CV, analog sequencer) with attenuator. The control input has polarizing function, i.e. the manually adjusted dividing factor can be modulated upwards or downwards. The basic idea of a polarizer is described in the modules A-133 Voltage Controlled Polarizer and A-138c Polarizing Mixer.

The output waveform is rectangle with 50% duty cycle. Unlike the A-115 with fixed dividing factors (2, 4, 8, 16) the dividing factor of the A-163 is voltage controlled and can be any integer value between 1 and about 20 (but only one output). In contrast to A-113 the dividing factor of the A-163 is voltage controlled and the output waveform is rectangle (the A-113 has 4 sawtooth outputs with 4 adjustable but not voltage controlled dividers).

Applications: dynamic voltage controlled frequency division of audio signals or modulation signals. More details concerning frequency division of audio signals can be found in the Trautonium or A-113 information.

A-165 : Dual Trigger Inverter/Modifier

Module A-165 (Dual Trigger Modifier) contains two separate trigger modifiers, to use with logical / digital levels (Gate, Clock, Trigger). Each half of the module enables signals generated by the A-100 to communicate with other instruments (such as an external sequencer), or is simply used where you want to reverse a trigger polarity.

Whatever signal is patched into the input is inverted by the module, and fed out of the Inv. Out (inverted output) socket. At the same time, a trigger signal of roughly 50 ms is generated every time an edge of the trigger pulse is sensed (negative as well as positive). This trigger signal is available at the +/- output

A-166 : Dual Logic Module

Dual logic module with 3 inputs for each unit. The logical states of the inputs ("1" = high / "0" = low) are linked together in 3 ways: AND, OR, EXOR (exclusive OR). The three functions are available simultaneously at three outputs with LED display of the output states. Additionally two inverters are available to obtain the inverted functions NAND, NOR and NEXOR. The sockets of each triple unit are "normalized", i.e. the switched contact of socket 2 is connected to input 1 and the switched contact of socket 3 is connected to input 2. Provided that no plug is inserted into socket 1 resp. socket 2 the socket is connected to the input above it. This simplifies the usage of the module when only 2 signals are combined. E.g. the logic functions AND and OR have different neutral input levels ("1" is the neutral state for AND, "0" is the neutral state for OR). In case of a fixed input level for the unused input one of the functions (AND or OR) would work no longer.

A-167 : Analog Comparator / Subtractor / Offset Generator

A-167 is a module that compares analog voltages and derives a gate signal. The state of the gate output (low/high) depends upon which of the voltages is higher. It is possible to compare two external voltages (+In and -In) or an external voltage (+In or -In) with a manually adjustable value (Offs. control). Both analog inputs +In and -In are equipped with an attenuator. Internally the module generates the voltage k1*(+In) - k2*(-In) + Offset and und sets or resets the gate output depending on the result of this internal voltage (>0V or <0V). The factors k1 and k2 represent the manual attenuators. A LED shows the current state of the gate output.

The Gap control is used to adjust a so-called "hysteresis". As long as this control is set to zero the switching levels for both on and off state of the gate signal are identical. As soon as the Gap control is turned up the switching levels for on and off state fall apart and a so-called hysteresis appears. The sketch at the bottom of this page shows the Gap function.

Normal and inverted gate outputs are available. In addition the internal voltage k1*(+In) - k2*(-In) + Offset is available at the Analog Sum socket. Consequently the module can be used as subtractor and offset generator too.

Applications: Generation of gate signals depending upon analog voltages. E.g. a gate signal that depends upon the present value of a LFO (triangle), ADSR or random signal can be generated and used to control a voltage controlled switch that on the other hand switches different control voltages or audio signals. The module can even be used to add the free-running mode to each ADSR ,e.g. A-140 similar to a LFO but with separate controls for rising and falling edge and exponential waveforms - in contrast to the linear waveforms of a LFO.

8 - Voltage Sources

A-170 : Dual Slew Limiter

Module A-170 contains two separate slew limiters, also known as portamento controllers or integrators. The first SL has just one joint control, which sets both rise and fall times (c. 0 ...10 sec). The second SL has separate controls for rise and fall times, and can therefore be used as a simple AR envelope generator. Over and above this, you can set the overall range for these parameters, with a three-position switch, as on the full ADSRs.

Both slew limiters have two LEDs each, to show the state of the rising and falling voltages.

A-171 : Voltage Controlled Slew Limiter

Module A-171 (VC Slew Limiter) is a voltage controlled slew limiter, otherwise known as a portamento controller or integrator. It is the voltage controlled versionof the A-170. Whenever there is an abrupt transition in the voltage present at the input, the Slew Limiter works as an integrator, slowing down the transitions in the output signal - so that abrupt transitions are sloped. The steepness of the slope is governed by the rate control.

As well as manual setting of this slope, the A-171 also gives you the possibility of voltage control of the slope's gradient by patching in an appropriate voltage to two CV inputs, one of which has an attenuator for level adjustment.

Two LEDs serve as status indicators to show the relative amounts of positive and negative signals at the output.

In combination with a MIDI interface (A-190 or A-191) the A-171 enables MIDI controlled slew rates.

A-172 : Maximum / Minimum Selector

A-172 is a minimum/maximum selector module and is equipped with four analog inputs and two analog outputs (minimum, maximum). The main application of the module is the processing/mixing of control voltages, e.g. random voltages, ADSR, LFO, S&H, ribbon CV, theremin-CV and similar, but even for audio signal processing the module can be used (e.g. several outputs of the same or different VCOs).

The module permanently picks the maximum resp. minimum voltage out of the four input signals and outputs these voltages to the maximum resp. minimum jack socket.

To adjust offset and amplitude for each input independently (i.e. to bring the signal into the right "position" with the desired level) we recommend to combine the module with the A-129-3 Slew Limiter/Attenuator/Offset Generator (see patch example below). The other sketch below shows the basic principle of the max/min module by means of three sine waves (e.g. three LFOs) with different frequencies and different levels.

A-174 : Joy Stick Module A-174 modules outputs 2 control voltages generated by a spring-loaded X/Y cross potentiometer (so-called joy stick). For each output the voltage offset (zero setting) can be adjusted. Each output is equipped with 2 LEDs for positive/negative display of the output voltages. If the spring is removed for one direction the joy stick is no longer spring-loaded for this direction (as the spring is destroyed when removed this cannot be re-established !).

A-175 : Dual Voltage Inverter

Module A-175 (Dual Voltage Inverter) is exactly what it says it is: two identical inverters, which will take a voltage and output it in an inverted form - so that an input of +5 V will be output as -5 V, an input of -2 V will be output as +2 V, and so on.

Two LEDs give a visual indication of the (positive or negative) output signal.

A-176 : Control Voltage Source

Module A-176 (Control Voltage Source) provides three voltage sources, to use wherever an extra CV is required. The top two voltage sources (CV 1 and CV 2) have controls for coarse and fine control of the voltage output; the third source (CV 3) just has the one control.

The range of the voltages output can be preset, either to 0 to +5 V or to -2.5 V to +2.5 V depending on your likely requirements. There is a jumper on the circuit board for each of the three voltage sources.

A typical use for the module would be to provide fine as well as coarse tuning for an A-110 standard VCO, (which, unlike the A-111, only has one tune control).

In general, this module will be useful whenever you need a manually controllable CV on a module which doesn't itself have a built-in control.

A-177 : External Foot Controller

Module for connecting 2 foot controllers and 1 double foot switch to A-100 for control of functions with your feet (e.g.VCF frequency, loudness, modulation depth, phasing, pitch). For each foot controller the input scale can be adjusted with a knob at the front panel. 4 outputs and 4 LEDs for CV1, CV2, Gate1, Gate2.

A special application of the A-177 is the usage within a Trautonium replica (for details refer to the Trautonium project article). The foot switches can be used to switch the mixtures of the subharmonic oscillator A-113. The foot controller can be used to control the overall loudness in combination with a VCA (A-130 or A-131).

A-177 is compatible with the footcontrollers FP5 and double foot switch VFP2 (see Accessories)

A-178 : Theremin Control Voltage Source

Theremin module for generating a variable control voltage by approaching/removing hand to/from an antenna. Additionally the module is equipped with a Gate output with adjustable threshold level. Probably the module will also be available in a version with a separate case so that the antenna can be placed outside the A-100. Controls/Inputs/Outputs: antenna input, offset (knob for zero adjust), 2 x CV out, 2 x LED (for CV control positive/negative and zero offset adjust)

To simulate the original Theremin two A-178, a VCO (e.g. A-110) and a linear VCA (e.g. A-130 or A-132) are required. But of course the A-178 can be used to control other functions in the A-100 (e.g. filter frequency, modulation depth and/or speed, tempo, attack/decay time and so on).

A similar module using the illumination intensity instead of the distance between hand and antenna is the Light-to-CV Converter A-179.

A-179 : Light Controlled Voltage Source

Module for converting different illumination intensities into corresponding analog voltage and a gate signal derived from the analog voltage. A sensor converts the illumination of the internal light sensor (light sensitive resistor / LDR) into a corresponding analog control voltage. The internal sensor is located at the front panel (int. LDR) of the module but a remote sensor may be connected via cable to the module (jack: ext. LDR). Thus the module A-179 is similar to the Theremin module A-178 but uses the illumination intensity instead of the distance between hand and antenna for generating the analog voltage.

9 - Auxiliary Modules

A-180 : Multiples 1

Module A-180 is a simple multi-connector. It has eight inter-connected sockets, so that you can patch more inputs or outputs into any module. The sockets can be split into two groups of four by disconnecting an internal solder bridge. Even though the A-180 is a very "primitive" low-level module it is required very often. Within a big A-100 system sufficient multiples should be planned.

A-181 : Multiples 2

Two multiples with one 1/4 jack socket and two 3.5mm jack sockets each, upper multiple is wired monophonic, lower is wired stereophonic.

A-185 : Bus Access

Active bus access module to feed CV and Gate into the A-100 bus (e.g. when using more than one frame or with external CV/Gate interfaces). Miniature jack sockets for CV In, Gate In, 2xCV Out, 2xGate Out, 2 LEDs for CV/Gate control.

In general the A-185 is recommended as soon as more than 2 VCO's (A-110, A-111) are controlled by the same control voltage source. Without interconnection of the A-185 in this case tuning inaccuracies (scale) may occur. The A-185 is mounted close to the VCOs. The controlling voltage for all VCOs is applied to the CV In socket of the A-185. By means of the CV line of the bus board the CV is connected to all VCOs at the same bus board.

A-188-X : BBD Module

This is the newest module manufactured by Doepfer. More information can be found at the Doepfer Website.

10 - Special Modules

A-190 : MIDI-to-CV/Gate/Sync Interface Module A-190 is a MIDI-CV/SYNC Interface, with which you can control any A-100 Module which has CV and gate/trigger input sockets by MIDI. The A-190 has two Digital-to-Analogue converters (DAC for short), which put out control voltages from 0 V to +5 V, so that you can control not just the pitch, but also another voltage-controllable parameter on the A-100. DAC 1 is 'hard-wired' to receive MIDI note messages and convert them into control voltages available at CV output socket CV 1. The DAC has 12-bit resolution, which gives excellent tuning resolution (in steps of 1/4096th). As a rule, DAC 1 will be used to control VCO pitch. DAC 2 can be assigned to your choice of MIDI controller. This DAC has 7-bit resolution (1/128th steps). Its output is available at CV 2, and can be used for voltage control of any suitable module (eg VCF, VCA, etc.).

The A-190 also has a clock output, controlled by MIDI clock. This can be divided down to provide a variety of clock outputs, and enable older sequencers or drum machines to be synced to MIDI. A Reset Output provides control of the A-160 / 161 Clock Divider / Sequencer or can produce MIDI-synchronised gates (for instance on an ADSR). MIDI START or CONTINUE messages make the voltage at the Reset output go low, and MIDI STOP messages make it go high.

In addition, the A-190 allows for portamento (glide) and pitch-bend, and provides a software LFO. These functions can all be switched on and off or altered by MIDI controllers. All control parameters can be saved in non-volatile memory.

A-191 : MIDI-to-CV Interface / Shepard Generator

Module A-191 is a combination of a MIDI-CV interface and a Shepard Generator. Most of the controls, indicators and in/outputs have a double function; there is a switch which toggles between the two sets of functions.

In use as a MIDI-CV interface, 13 of the 16 control voltage outputs are dedicated to sending voltages converted from a particular MIDI controller (such as Mod Wheel, Volume, Pitch Wheel, Aftertouch, etc.). Controller messages on your chosen MIDI channel are converted into voltages in a range from 0 to 5 V. The other three sockets output an internal LFO generated in sync with MIDI clock, in three waveforms: sawtooth, triangle and rectangle.

In use as a so-called Shepard Generator, the sockets output eight different phases each of a triangle and sawtooth wave. The Shepard Generator creates in combination with other modules (VCO's, VCF's, VCP's, VCA's, Mixers) psycho-acoustic so-called Barberpole effects like never ending rising (or falling) phasings (with VCPs), filterings (with VCF's) or tones (with VCOs). To create the Barberpole effect you need the required additional modules in your system. For a good Barberpole effect we recommend a minimum of 4 VCP's (or VCF's or VCO's) and 4 VCA's (linear types A-130 or A-132). With 8 modules instead of 4 the sound becomes more smooth and tight.

All A-191 settings can be saved into non-volatile memory.

A-192 : Voltage-to-MIDI Interface CVM16

Module A-192 is a CV-to-MIDI interface that converts 16 control voltages in the range 0...+5V into 16 MIDI controller messages. A-192 is the modular version of Pocket Control with the 16 rotary controls replaced by 16 miniature jack sockets to process any control voltages instead of the manually generated voltages of Pocket Control.

MIDI messages appearing the MIDI Input are merged to the MIDI controller messages generated by the A-192.

128 different assignments (Presets) of the 16 CV inputs to MIDI controller messages are available. Switching between the 128 presets takes place with an 8-pin DIP switch on the pc board (permanently) or via incoming MIDI program change messages (temporarily).

If none of the 128 factory presets is suitable new presets can be made with the Pocket Control editor which is available for free on our web site. Please look at the Pocket Control manual for details concerning the available factory presets until the English manual for A-192 is available.

The snapshot button transmits the 16 momentary states of the 16 inputs as MIDI controller messages.

A-196 : Phase Locked Loop

Module A-196 contains a so-called phase locked loop (PLL). The basic PLL system is shown in the sketch at the bottom of this page. A PLL consists of three parts: voltage-controlled oscillator (VCO), phase comparator (PC), and low-pass filter (LPF). All parts are normally connected to form a closed-loop frequency-feedback system.

This is how a PLL works: The output of the internal VCO (linear CV control, rectangle output) is compared with an external signal (e.g. the rectangle output of a A-110 VCO) in the so-called phase comparator (PC). The output of the phase comparator is a digital signal (low/high/tristate) that indicates if the frequency resp. phase difference of the two input signals is negative, zero or positive. The output of the phase comparator is processed by a low pass filter (LPF) to generate a smooth voltage that is used to control the frequency of the internal VCO. The 3 units VCO, PC and LPF form a feedback loop that works like this: The control voltage (output of the LPF) increases as long as the external frequency is higher than the frequency of the internal VCO und stops increasing when both frequencies become identical. The control voltage decreases as long as the external frequency is lower than the frequency of the internal VCO und stops decreasing when both frequencies become identical.

But there are some stumbling blocks: Different types of phase comparators with advantages and disadvantages an be made. Some phase comparators e.g. even lock at harmonics, i.e. if the two frequencies to be compared are integer multiples. But for some applications this can be used to create interesting effects. The A-196 contains 3 different types of phase comparators: PC1 is a simple exclusive OR, that even locks at harmonics. PC2 is a so-called RS flipflop and PC3 a more complex digital memory network. The user can select one of the three phase comparators with a 3-position switch. When PC2 is used a LED displays the "locked" state, i.e. when the frequency of the internal VCO is identical to the external frequency.

Special attention has to be directed to the frequency of the LPF. To obtain a smooth control voltage for the VCO the frequency of the LPF has to be much smaller than the lowest frequency of the internal or external audio signal. Otherwise the frequency of the internal VCO will jitter or wobble around the correct frequency. But for special effects this frequency jitter can be used intentionally. Example: frequencies in the range 50Hz...1kHz have to be processed with the PLL. Therefore the frequency of the LPF has to be about 10Hz or even less. Such a low frequency of the LPF causes a noticeable slew of the internal VCO. When the frequency of the external signal jumps e.g. between 500Hz and 1kHz it takes about 0.1 second until the internal VCO reaches the new frequency (like portamento). So one has to find a compromise between frequency jitter and portamento. But these remarks are valid only for the "ideal" working PLL. As the A-196 is used in a musical environment the "problems" and disadvantages with jitter and slew time lead to additional musical applications like portamento effects, wobbling frequencies or harmonic locking according to the type of frequency comparator and time constant of the PLL low pass filter. Instead of the internal manually controlled low pass filter the voltage controlled slew limiter A-171 can be used to obtain voltage control of this parameter. Normal audio filters (e.g. A-120, A-121) cannot be used for this job as the minimum frequency is to high (down to a few Hz or even less necessary) and the signal has to be DC coupled due to the low frequencies. Audio filters are normally AC coupled.

Another very important application of a PLL is frequency multiplication in combination with an external frequency divider. For this the output of the PLL-VCO is processed through an external frequency divider (e.g. A-163, A-160, A-161, A-115) before it is fed to In1 of the phase comparator. In this case the frequency of the PLL-VCO will be a multiple of the master frequency. E.g if the the A-163 is used and adjusted to dividing factor 5 the frequency of the PLL-VCO will be 5 times the frequency of the master VCO. Consequently frequency division (A-163) leads to frequency multiplication with the PLL circuit. In combination with the PLL low pass frequency several effects can be realized (frequency multiplication with portamento or wobbling). The frequency multiplication can even be used to drive a graphic VCO. If your graphic VCO e.g. has 8 steps (e.g. A-155) and you use a frequency divider with factor 8 in the PLL feedback the output of the graphic VCO has the same frequency as the master VCO. Another application is the generation of pseudo-harmonics (not real harmonics as only rectangle waves are available) or clock generation for switched-capacitor filters.

The PLL components are available as separate building blocks in the A-196 module. The standard PLL patch is realized by means of normalized sockets. But it is also possible to use each component separately. E.g. the VCO can be used as a simple VCO with linear control input and rectangle output. For this an external voltage has to be fed into the CV input socket. The VCO has two controls: Offset and range (switch). As the VCO has a linear control input the frequency will go down to zero (i.e. the VCO stops) if the input CV is 0V. The offset control is used to adjust the lowest frequency (i.e. the frequency for CV = 0V). The range switch is used to switch between 3 frequency ranges. The position of the switch defines the max. available frequency (detailed specifications will follow).

For other treatments of the phase comparator output (e.g. with an external voltage controlled filter or any other processing module) the output of the phase comparator is available. Same applies to the LPF output and input 1 of the phase comparator.

It has to be pointed out that the A-196 is a very experimental module and its functions cannot be described straight forward as for other modules. Rather the user should try out the possibilities by trial and error. Some patches and sound examples can be found at the end of this page.

A-197 : Analogue Meter

This module serves to display DC or AC voltages by means of an illuminated moving coil meter with mirror scale. The display range is 0...+10V (resp. -5V...+5V in the offset mode). The module features 3 different measuring methods that are selected by a toggle switch:

The measuring input is available as a triple multiple so that the signal to be measured can be used in the system simultaneously. A LED is used as an indicator for negative voltages.

A-198 : Trautonium Manual / Ribbon Controller

Module A-198 is a Trautonium Manual resp. Ribbon Controller. The controlling element of the A-198 is a linear position sensor (length about 50 cm) that has available a pressure sensor too.

Touching the sensor with a finger generates a control voltage CV1 that is proportional to the position of the finger. The scale (i.e. the relation between position difference and voltage difference) is adjustable with a potentiometer at the front panel. A hold switch is used to determine if the CV voltage is held after removing the finger (hold = on) or if the CV voltage jumps to 0V (hold = off). In the last case (hold = off) a gate signal is derived from the CV voltage whenever a finger touches the sensor (e.g. for triggering an envelope generator).

A pressure sensor located below the position sensor generates a second control voltage CV2 that increases with higher pressure of the finger. Even for CV2 the scale is adjustable. A second gate signal is triggered as soon as the pressure exceeds a certain value. The gate threshold is adjustable at the front panel. The pressure sensor is made with conductive rubber (located below the position sensor) and works not as accurate as the very precise position sensor. The resistance of the conductive rubber changes with varying pressure and causes a variable voltage. But the coherence between pressure and resistance/voltage is not very accurate - except that an increasing pressure will cause an increasing voltage. Even some difference of the pressure sensor behaviour over the length of the manual may be possible as the conductive rubber has tolerances over this length.

The sensors are located in a separate metal frame (length about 600 mm, width about 30 mm, height about 18 mm, weight: about 900 g, color: silver-grey). The connection between the module and the sensor frame is made by a 4 pin cable (same as used for USB connections). ''' A-199 : Spring Reverb'''

Module A-199 is a spring reverb module. The reverb effect is electronically simulated by means of 3 spiral springs. Spring reverb systems have a very characteristic sound that is based on the (insufficient) mechanical properties of the springs like signal delays, audio resonances, limited frequency range, acoustic feedback behaviour, sensitivity to mechanical shocks and others.

The 3-spring system used in the A-199 ensures a "dense" reverb because of the different properties of the three springs.

The A-199 implies some special features that are not self-evident for spring reverb units:

The reverb signal can be fed back to the input using the Feedback control. Even self-oscillation of the springs similar to the self-oscillation of filters is available. The feedback loop can lead even via external modules like VCA, VCF, phaser, frequency shifter, vocoder, distortion/waveshaper, ring modulator and others. In this case the reverb output of the A-199 is connected to the input of the external module(s) and the output of the external module(s) is fed back to the Ext.Feedback In socket of the A-199. This socket contains a switch that interrupts the internal feedback loop as soon as a plug is inserted.

Another feature is the Emphasis control. This enables the adjustment of the accentuation of middle frequencies (around ~ 2kHz).

External links

 

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