Doepfer A-127 User Manual
doepfer
In Level
Audio
A-127
Audio
In
ext. CV
VCF 1
Audio
Out
VCF 2 VCF 3
Mix Out
VCRF
LFO Frq.
CV Ampl.
VCF Frq.
Resonance
Audio Lev.
Original
System A - 100
1. Introduction
Module A-127 is a Voltage-Controlled Triple Resonance Filter
filters with one common input.
For each of the filters, the
nance can be manually controlled, and in addition
the filter frequency can be voltage controlled. Each
filter has its own audio output. There is also a Mix
output which takes your chosen amounts of each of
the three filter outputs and the original signal - set by
the Audio Level controls - and outputs them from one
socket.
Each of the filters also has an internal LFO (a triangle
waveform) for modulating the filter, and there are
controls for LFO frequency and amplitude. Instead of
the LFO, an external control voltage can be used,
whose amplitude can be manually controlled.
H
Triple VC Resonance Filter
), consisting of three separate
filter frequency
There is an alternative scenario:- each of the
three filters can also be configured as a
12dB low-pass filter
trol. To do this, a jumper has to be repositioned on each of the three circuit boards
(see chapter 7, Appendix).
with resonance con-
A-127
band pass
and
Reso-
1
A-127
Triple VC Resonance Filter
System A - 100
doepfer
2. VCRF - Overview
A-127 VCRF
➃
ext. CV
1
2
3
Audio
In
➁
LFO Frq.
0
0
0
0
Audio In
Level
➂ ➄ ➅ ➆
Triple Voltage Controlled Resonance Filter
CV Ampl. VCF Frq. Resonance Audio Level Audio
10
10
10
10
10
0
10
0
10
0
1 s ame circuit
2 s ame circuit
3
F
ext. CV Out
LFO
A L
0
0
0
F Q
VCF
10
10
10
0
0
0
Out In
M
I
X
10
0
10
0
10
0
L
0
Original
L
Out
VCF 1
10
VCF 2
10
VCF 3
10
Mix
10
➀➇
2
doepfer
System A - 100
Triple VC Resonance Filter
A-127
Controls:
A. In Level : Input signal attenuator
1
per VCF:
LFO Frq. : LFO frequency control
2
3 CV Ampl. : Attenuator for external CV and/or
LFO amplitude
LED : LFO and/or external CV indicator
4
5 VCF Frq. : Filter frequency control
Resonance
6
Audio Level : Level control for audio output
7
Original : Control for setting the amount of
8
(*) For modules manufactured until end of 1998 control
7 affects both the individual outputs § and the mix
output $. For modules manufactured 1999 and later
control 7 affects only the mix output $, but not the
single outputs §.
: Filter resonance control
amplitude of the filter (*)
the original signal present at the
Mix output
$
In- / Outputs:
Audio In : Input to the filter
!
per VCF:
ext. CV : Filter frequency CV input
"
§ Audio Out : Filter output
Mix Out
$
:Mix output
3
A-127
Triple VC Resonance Filter
System A - 100
doepfer
3. Basic function
The A-127 is a triple resonant filter containing three
band-pass filters each with controllable filter frequency
, resonance and amplitude. What a band-pass filter
f
M
does is to attenuate signals in frequency ranges both
above and below the filter frequency - referred to here
as the middle frequency - resulting in a bell-shaped
response curve (see fig. 1). In this way, a particular
part of the audio spectrum can be singled out.
Out
fig. 1: Frequency response of a band-pass filter
VCF Frq. / CV VCF Frq. / CV
f
M
Freq.
Out
M
with lower (on the left) and higher resonance
Freq.f
band let through, and the Audio Level control to set the
volume (see fig. 1).
To make it easier to understand how the A-127 is
configured, fig. 2 shows a block diagram of the
internal components.
ext. CV
LFO
ext. CV
"
Audio O ut§Mix Out
$
CV Ampl.
Audio
Audio In
!
3
Frq.
5
VCF
Res.
6
Level
7
1
Mix
2
Original
Frq.
2
In Level
1
8
3
For each filter you use the frequency control to determine the exact position along the frequency axis, the
resonance control to set the width of the frequency
4
fig. 2: Internal construction of the A-127 (from 1999
output § is not affected by the level control 7)
Loading...