Technical Details A-100

The Principles of Voltage Control

What makes analogue synthesizers (and modular systems in particular) special is that the important parameters of the sound sources (VCO, noise, etc.) and modifiers (VCF, VCA, etc.) can be altered not just by hand, but by voltage control.
This principle was turned into reality by the "father of the analogue synthesizer", Robert Moog, who produced the first commercially available synthesizer in the sixties. It gives vast flexibility and the potential to make sounds that have never been made before.
Fig. 1 shows the principle of voltage control, with examples of control voltages affecting a filter (VCF) and an oscillator (VCO).
In the case of the VCF, the parameter which is being voltage-controlled is the Cut-Off Frequency fc. The amount of control voltage input present changes the cut-off frequency, and thus the frequency of the signal that the VCF lets through - see the shaded area in the diagram.

Fig.1: The principles of voltage control

In the case of the VCO, it’s the pitch which is controlled by a voltage: an increase of 1 volt corresponds to an increase of one octave in the pitch.
With a sudden change of voltage, the pitch changes suddenly, while with a smoother, continuous change, portamento is created.
As well as modules which can be affected by voltage control, there are other modules like the ADSR and LFO which themselves produce voltages to control other modules.
Usually, these modules need a Trigger Signal to bring them into action. For instance, a GATE Signal, corresponding to a key being pressed on a keyboard, can set off an ADSR, which then puts out its variable voltage "envelope" to affect other modules.

Fig. 2: The envelope generated by an ADSR

Signals in the A-100

In the System A-100 there are three types of signal:

Audio Signals are produced by the sound source Modules (such as VCO or NOISE), and lie in the range from -5 V to +5 V (10 VSS). The System A-100 can also let you use external Audio Signals (e.g. Microphone, Electric Guitar, Keyboard).
To interface satisfactorily, the level of external Audio Signals must be brought up to the A-100’s operating level.
Module A-119 (External Input), is ideal for this job, having among other things an internal pre-amp, and two inputs of different sensitivity.
Control voltages, as produced by modulation sources like the LFO and ADSR, are from -2.5 V to +2.5 V (5 VSS) for the LFO, and from 0 V to +8 V for the ADSR.
Trigger or Gate Signals, which start a process or function, are typically from 0 V to 5 V, with the trigger occurring as the leading edge of the waveform shoots up from 0 V to 5 V.
These definitions of the various signals, and the distinctions between them - sound sources and modulation sources - are right in principle, but a modular system like the A-100 often makes a mockery of them. In a modular set-up, all of the modules produce voltages, and can be used as control voltages or triggers, thus blurring the distinction between the various types.
For example, the output from an LFO can be used as an audio signal, as a control voltage for a VCF or VCA, or as a trigger signals for a sequence.
It’s just about true to say that anything can be modulated by anything else, so that a modular system gives the musician extraordinary flexibility and individuality.

Power Supply and System Bus

The A-100’s System Bus  ,i.e. the bus board(s), supplies power to the modules. The A-100 modules need the voltages +12V and -12V - some modules additionally +5V (e.g. A-113, A-190, A-191). The voltages +12V and -12V are supplied by the A-100 Standard Power Supply (see A-100 accessories). This power supply is built into the basic frames (3HU and 6HU) and has a max. current of 650mA for both +12V and -12V. If one of modules used in the A-100 system requires +5V (e.g. A-113, A-190 or  A-191) the additional +5V power supply has to be built into the frame (see A-100 accessories). If not more than 100mA are required at +5V the +5V low cost adapter can be used instead of the separate +5V power supply (see A-100 accessories). In this case the required current @+5V is taken from the +12V line. Of course there has to be a sufficient current reserve at +12V.
If you want to run only one or a few modules the A-100 Miniature Power Supply can be used instead of the A-100 standard power supply (see A-100 accessories). It supplies max. 100mA@+12V/-12V and additionally 50mA@+5V.
The system bus also carries the internal control system (INT.GATE and INT.CV), which some of the modules (such as the VCO A-110, or ADSR A-140) can tap into. You can choose whether these modules receive these signals, by altering an internal jumper.

Fig. 3: The A-100 system bus

If you want to run single A-100 modules without using our bus board, power supply and frames here is the pin-out for module's bus connectors.

Pin out of the module's power supply connectors

Both the 10 pin and the 16 pin version of the bus connection have available the standard power supply (-12V, GND, +12V). In addition the 16 pin version of the bus connection has the three signals +5V, CV and Gate available at the module's connector (e.g. CV is used at the standard VCO A-110 or Gate is used at the envelope generator A-140). Modules that make no use of these additional signals normally use only the 10 pin version of the bus connection.

Pay attention that applying other than the described voltages or changing the polarity will result in the module’s instant destruction !

If you use the A-190 MIDI-/CV-Interface in your system, when you press a key on your MIDI keyboard, the gate and CV1 signals from the A-190 will be sent via the INT.GATE and INT.CV to all modules on the bus. The INT.GATE and INT.CV signal busses can be split into two equal halves by removing jumpers J1 and J2 (see Fig. 3), so that for each whole bus, you can have two separate CV/GATE subsystems.
If on the other hand you’d like to have the same internal CV and gate available on two busses at once, you need to link the two together, with the special CV/gate leads, the A-100 BC.

This is how you go about it:

A Make absolutely sure that you connect the leads correctly, joining up the upper INT CV with the lower INT CV, and the upper INT GATE with the lower, to avoid possible damage when you switch back on!

Fig. 4: Making a common INT.CV and INT.GATE signal path between the upper and lower busses.

If you use more than one frame we reccomend the A-185 Bus Access module to interconnect CV and Gate between different frames. This module enables the access to the system bus (CV and Gate) with active regeneration amplifiers for CV and Gate signals to compensate voltage losses which may occur if only passive connections are used.

Fig 5: Making a common system bus when using different frames

Important in case of A-190 use:

If you want to control the A-100 system bus with the A-190 module you have to disconnect the internal connection of the A-190 to the system bus (for details see A-190 user's manual).

Interconnecting modules

For connecting modules to each other, you need mono miniature jack (Æ 3.5 mm) patch leads. You can obtain patch leads from us in different lengths and colors: 30cm, 50cm, 80cm and 120cm. For details see A-100 accessories.

Integrating the A-100 with MIDI

To link the A-100 into a MIDI system, you can use one of our external MIDI interfaces like our MCV4, MCV24 or MSY2. The A-100 systems offers the MIDI interfaces A-190, A-191 and A-192.

The MIDI-CV/SYNC Interface A-190 is the standard MIDI interface of the A-100 and has the following outputs available:

The A-190 automatically sends pitch control CV and gate information out on the INT.CV and INT.GATE busses.

Module A-191, as well as being a Shepard Generator, is also a MIDI-CV Interface, with 16 CV outputs linked to MIDI Controllers (such as Volume, Velocity, Modulation, Pitch Bend, etc.) on the MIDI channel of your choice.

Latest of the MIDI-CV Interfaces is the 24-channel MCV24, a 19" rackmount with its own power supply available end of 1998. The MCV 24 has 24 Outputs, providing MIDI control of all voltage-controllable aspects of modules (for instance CV, Gate, Pitch, Velocity, After-Touch, Continuous Controller, etc.). Each of the 24 outputs may be used a analog voltage (CV, Pitch, VCF-CV ...) or digital voltage (Gate, Trigger). The MCV24 also has 2 additional Digital Outputs available working as Clock and Start/Stop.

VC Modules like all VCO's, VCF's, VCA's or the A-141 VC-ADSR, A-142 VC-Decay/Gate or A-147 VC-LFO can be controlled via the A-191 or MCV24, so that, for instance, a continuous MIDI controller or velocity or after touch can alter envelope parameters in real time. Since these controllers can be recorded by a MIDI sequencer, VC modules are effectively programmable.

The A-192 CV-to-MIDI interface enables the conversion of A-100 control voltages into MIDI controller messages (e.g. Theremin, Vocoder, A-119 envelope, Random, LFO usw.).

Analog sequencing can be provided by A-155 or the Doepfer MAQ 16/3 MIDI Analog Sequencer. The MAQ16/3 is eqipped with3 CV and 3 Gate outputs compatible with the A-100 system.

For 8-track rhythm sequencing with MIDI sync Doepfer’s SCHALTWERK or REGELWERK is ideal. Both devices are equipped with 8 CV (Schaltwerk: 16 CV) and 8 Gate outputs compatible with the A-100 system.