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doepfer System A - 100 18dB Low Pass A-103

1. Introduction

Module A-103 (VCF 6) is a voltage controlled low-

pass filter with a cut-off slope of -18dB/octave. It

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.

Resonance (or Emphasis) is adjustable all the way up

to self-oscillation - in which case the filter behaves like

a sine wave oscillator.

A-103 uses a so-called transistor ladder with a slope

of 18 dB/Octave as frequency controlling element. It is

very similar to the transistor ladder of the A-120 (24dB

Moog type low pass) but the ladder of the A-103 is a

modification of the original Moog ladder and identical to

the ladder used in the Roland TB-303 (base and

collector of each transistor are connected).

CV 1

Resonance

CV 3

CV 2

Audio In

Level

Audio

Out

CV 2

Frequency

A-103

VCF 6

CV 3

Summary of content (6 pages)

PAGE 1
doepfer System A - 100 18dB Low Pass A-103 1. Introduction CV 1 A-103 VCF 6 CV 2 CV 2 CV 3 CV 3 Frequency Level 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.
PAGE 2
A-103 18dB Low Pass Controls: 2. VCF 6 - Overview 1 Freq.: Cut-off frequency control 2 CV 2: Attenuator for CV at input " 3 CV 3: Attenuator for CV at input § 4 Lev.: Attenuator for audio input $ À 5 Res. : Control for setting the filter’s resonance (emphasis) Á In / Outputs: A-103 VCF 6 18 dB LOW PASS CV 1 Frq. Ê 0 CV 2 10 CV 2 Ë 0 CV 3 10 CV 3 Ì 0 Lev. Í Res.
PAGE 3
doepfer System A - 100 3. Controls Out 18dB Low Pass A-103 Frq. / CV 1 Frq. as a special effect. Res. With this control you adjust the Cut-Off Frequency fc, above which the filter attenuates all frequencies. At 10, the filter is fully open. The more you turn down this control, the more the high frequencies are filtered. The sound becomes mellower and less bright (see Fig. 1) until at 0 the filter is completely shut, and there will be no output signal at all.
PAGE 4
A-103 18dB Low Pass System A - 100 4. In / Outputs ! CV 1 Socket CV 1 is the filter’s standard voltage control input, and works on the 1V / octave rule, like the VCOs. If you patch a modulation source (eg LFO, ADSR) to this input, the cut-off frequency of the filter will be modulated by its voltage: ie., the sound color changes according to the voltage put out by the modulator. doepfer $ Audio In This is the filter’s audio input socket. Patch in the output from any sound source (eg.
PAGE 5
doepfer System A - 100 5. User examples As the A-103 is very similar to the A-102 please refer to the user examples of the A-120. The filter’s cut-off frequency can be modulated in various ways. The basic modulations types are: 18dB Low Pass A-103 But even other voltage sources may be used to control the frequency of the A-103: e.g.
PAGE 6
A-103 18dB Low Pass doepfer System A - 100 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. A-103 VCF 6 CV 1 Frq. 0 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.