Doepfer A-101-1 User Manual
doepfer
System A - 100
Vactrol Multitype Filter
A-101-1
1. Introduction
Module A-101-1 is a special multitype filter based on
an idea by Nyle A. Steiner from the year 1974. Injecting
an audio signal into different points of a standard low
pass filter circuit leads to the three filter types low pass
(LP), band pass (BP) amd high pass (HP). For each
filter type a separate input
the three filtered signals appears at the common out-
put. Even a notch filter can be realized.
In contrast to the original circuit so-called
used instead of diodes as variable resistors for fre-
quency and resonance control. A vactrol is a combination of a light depending resistor (LDR) and a light
emitting diode (LED) both put into a small light-proof
case. Vactrol based circuits are known for their soft
low-distortion sound. For details about vactrols and
the A-101-1 circuit principles please use the corresponding links in the A-101-1 info page on our web site
www.doepfer.com.
The three filter audio inputs are normalled via swit-
ching sockets, i.e. the BP input is connected to the LP
jack socket provided that no cable is plugged into the BP
socket (same applies for HP/BP inputs). Each audio
input is equipped with an attenuator. The audio inputs
are very sensitive and enable distorted sounds too.
For both frequency and resonance manual control and
several control voltage inputs are available.
Two LEDs display the current frequency and reso-
nance settings.
is available and the sum of
vactrols
are
1
A-101-1
Vactrol Multitype Filter
System A - 100
doepfer
2. Overview
a
9
!
1
"
2
§
3
$
4
%
5
Controls:
1 Frequency manual frequency control
2 CVF2 attenuator for FCV input "
3 CVF3 attenuator for FCV input §
4 Emphasis manual resonance control
5 CVQ2 attenuator for QCV input %
&
6 LP attenuator for LP audio input &
6
7 BP attenuator for BP audio input /
8 HP attenuator for HP audio input (
/
9a/b LED controls for frequency and resoance
7
Inputs / Outputs:
(
! CVF In 1 frequency control voltage input 1
" CVF In 2 frequency control voltage input 2
8
§ CVF In 3 frequency control voltage input 3
$ CVQ In 1 resonance control voltage input 1
a
)
% CVQ In 2 resonance control voltage input 2
& LP In low pass audio input
b
)
/ BP In band pass audio input
( HP In high pass audio input
b
9
)a Out 1 audio output 1
)b Out 2 audio output 2
2
Loading...