Manual

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System A - 100 A-105 / A-122

1. Introduction

The modules A-105 and A-122 are voltage-

controlled low-pass filters, which filter out the higher

parts of the sound spectrum, and lets lower frequen-

cies 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

Voltage controlled resonance: for both A-105 and

A-122, 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.

The A-105 is based on the special circuit SSM2044,

that was used in several devices of the companies

Korg (Polysix, Mono-Poly), Sequential Circuits

(Prophets, Pro-One), PPG, Fairlight, Emu and Kawai.

The circuitry of the A-122 uses a chip of Curtis Elec-

tromusic (CEM), and is very similar to the classic

Oberheim filter sound. Because of the different cir-

cuits the A-105 and A-122 have considerably different

sounds and even sound different compared to the

other filters (e.g. A-120 Moog low pass, A-102 Diode

Low Pass or A-103 18dB low pass, A-124 Wasp filter).

As the functions and controls are the same for both

modules they are a combined in one manual.

FCV 1

Resonance

FCV 2

QCV

Audio

Level

Audio

Out

QCV

Frequency

A-122

VCF 3

FCV 2

Summary of content (8 pages)

PAGE 1
System A - 100 doepfer A-105 / A-122 1. Introduction Level Audio In A-122 VCF 3 FCV 1 FCV 2 FCV 2 Frequency QCV QCV Audio Out Resonance The modules A-105 and A-122 are voltagecontrolled low-pass filters, which filter 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).
PAGE 2
A-105 / A-122 System A - 100 Controls: 2. VCF 3 - Overview A-122 VCF 3 24 dB Low Pass II Audio In Lev. 0 ➀ 10 FCV 1 Frq. 0 10 0 10 Attenuator for audio input ! 2 Frq. : Cut-off frequency control 3 FCV : Attenuator for filter CV at input § 4 QCV : Attenuator for resonance CV at input $ 5 Res.: Control for setting the filter’s resonance (emphasis) In / Outputs: FCV 0 1 Lev.
PAGE 3
doepfer System A - 100 3. Controls A-105 / A-122 CV 1 Lev. Use this attenuator to control the amount of signal entering the filter input $. Out H If the filter’s output sounds distorted, turn this control down, unless you deliberately want the sound as a special effect. 2 Freq. With this control you adjust the Cut-Off Frequency fc, above which the filter attenuates all frequencies. At 10, the filter is fully open.
PAGE 4
A-105 / A-122 System A - 100 At close to maximum resonance, the filter starts to self-oscillate, and behaves like a sine wave oscillator. Thanks to this effect, you can use the filter as an independent tone source. am plit ude doepfer 4. In / Outputs ! Audio In This is the filter’s audio input socket, where you patch in the output from any sound source. " FCV 1 re s onan ce Socket FCV 1 is a voltage control input for the filter. It works on the 1V / octave rule, like the VCOs.
PAGE 5
doepfer System A - 100 $ QCV This socket is the voltage control input for the filter’s resonance. If you patch a modulation source (eg LFO, ADSR) to this input, the resonance of the filter will be modulated by it: increases in voltage will increase the amplitude of the frequencies around the filter cut-off point. % Audio Out Filter output % sends out the filtered audio signal. A-105 / A-122 5.
PAGE 6
A-105 / A-122 System A - 100 A-121 multi-mode filter’s 12 dB) with voltage controlled resonance. To create a bandpass filter, put both modules in series (see Fig. 3). The band-width is governed by the difference between the cut-off frequencies of the two filters fL (A-122) and fH (A-123); the middle frequency is half way between the two: fM = (fL + fH ) / 2. doepfer Freq. Ö f A-122 Freq. Ö L A-138 A-123 A-122 A -123 f Freq. Ö M F re q Ö . Freq. Ö Freq. Ö fL f Freq. Ö M Fig.
PAGE 7
doepfer System A - 100 A-105 / A-122 Further examples can be found in the manual for the A-123 high pass filter.
PAGE 8
A-105 / A-122 System A - 100 doepfer 6. Patch-Sheet The following diagrams of the module can help you recall your own Patches. They’re designed so that a complete 19” rack of modules will fit onto an A4 sheet of paper. Photocopy this page, and cut out the pictures of this and your other modules. You can then stick them onto another piece of paper, and create a diagram of your own system. A-122 V CF 3 A-122 V CF 3 Audio In Audio In Audio In 0 10 P 8 • Draw in patchleads with colored pens.