Doepfer A-130, A-131 User Manual
doepfer System A - 100 VCA A-130 / A-131
1. Introduction
Modules A-130 (Linear VCA) and A-131 (Exp. VCA)
CV 1
A-130
provide voltage-controlled amplification.
CV 2
In 1
In 2
CV 2
A udio
In 1
Audio
In 2
V CA-LIN.
Gain
Audio Out
Out
H This section of the manual applies equally to
the A-130 and A-131, because apart from the
one difference of their response curves, they
are otherwise identical.
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 attenua-
tor. They are amplified by an amount determined by the
combination of the gain and the two CV controls.
1
A-130 / A-131 VCA System A - 100 doepfer
2. VCA - overview
A -130
CV 1
Ê
CV 2
Ë
Audio In 1
Ì
Audio In 2
Í
Audio Out
Î
VCA-LIN.
Gain
10
0
CV 2
0 10
In 1
10
0
In 2
10
0
Out
0 10
À
Á
Â
Ã
Ä
Controls:
1 Gain: Overall gain control
2 CV 2: CV attenuator for input "
3 IN 1: Attenuator for audio input §
4 IN 2: Attenuator for audio input $
5 Out: Attenuator for the output signal
In / Outputs:
! CV 1: Control voltage input
" CV 2: ditto, with attenuator
§ Audio In 1: Audio input
$ Audio In 2: ditto
% Audio Out: Audio output for the combined audio
signals input at § and $ and then
amplified by the VCA.
2
doepfer System A - 100 VCA A-130 / A-131
3. Controls
The A-130 has a linear response: the amplification is in
direct linear proportion to the control voltage input (see
Fig. 1).
The A-131 has an exponential (or logarithmic) response. That means that control voltage changes have
less effect at low levels of amplification than at high
levels, and makes the A-131 more sensitive and suitable for subtle changes at low levels (see Fig. 1).
10
lin.
5
e xp.
0
5 10
Control Voltage
èè
1 Gain
This controls the overall gain of the VCA.
At "0", with no control voltage present, there is no
amplification at all: no signal is present at the VCA’s
output. Once the gain control is turned up, amplification
occurs, even if there is no CV input present. The gain
control shifts the whole VCA response upwards (see
Fig. 2).
10
lin.
5
Ga in = 3
0
Control Voltage
e xp.
5 10
èè
Fig. 1: Response curves for the A-130 and A-131
Fig. 2: Effect of gain control on VCA response
3
Loading...