Doepfer A-103-18dB User Manual

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

1. Introduction

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

CV 2

CV 1

A-103

VCF 6

CV 3

L evel

CV 2

CV 3

Aud io In

Aud io
Ou t

Freque ncy

Resona nce

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).

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

2. VCF 6 - Overview

A -103

18 dB LOW PASS

CV 1

Ê

0

CV 2

Ë

0

CV 3

Ì

0 10

Audio In

Í

0 10

Audio Out

Î

0 10

VC F 6

Frq.

10

CV 2

10

CV 3

Lev.

Res.

À

Á

Â

Ã

Ä

Controls:

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 $
5 Res.: Control for setting the filter’s reso-

nance (emphasis)

In / Outputs:

! CV 1: Control Voltage input
" CV 2: ditto, level controlled by 2

§ CV 3: ditto, level controlled by 3
$ Audio In: Audio input to the filter
% Audio Out: Audio output from the filter

2