doepfer
A-175
VOLT. INV.
In
System A - 100
1. Introduction
Module A-175 (Dual Voltage Inverter) is exactly what
it says it is: two identical inverters, which will take a
voltage and output it in an inverted form - so that an
input of +5 V will be output as -5 V, an input of -2 V will
be output as +2 V, and so on.
Dual Voltage Inverter
A-175
In
Inv.
Out
In
In
Inv.
Out
Two
negative) output signal.
give a visual indication of the (positive or
LEDs
1
A-175
Dual Voltage Inverter
System A - 100
doepfer
2. Overview
A-175
VOLT. INV.
In
In
Inv.
Out
Ctr.
-
In
In
Inv.
Out
Ctr.
-+
Indicators
LEDs : Visual indicators of the state of the
1
output voltage (positive or negative)
In- / Outputs
In : Voltage input, linked to input
!
" In : Voltage input, linked to input !
Inv. Out
§
+
➀
: Inverted voltage output
"
2
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System A - 100
Dual Voltage Inverter
A-175
3. Indicators
1 LEDs
Visual indicators of the state of the output voltage
(positive or negative) at socket §.
4. In- / Outputs
! In • " In
Sockets ! and " are the internally linked
the A-175. This is where you patch in the signal you
want to invert.
inputs
P Since in practice you very often need the
original signal as well as its inversion (see
user examples), you can use the second
socket as a mini-multiple.
§ Inv. Out
The inverted voltage is output at socket
§
.
for
3
A-175
R
Dual Voltage Inverter
System A - 100
doepfer
5. User examples
Panning
Fig. 1 shows a typical patch to create Panning - the
shifting of a sound’s position in the stereo picture.
The input signal is simultaneously sent to two linear
VCAs, whose outputs are sent one to the left (Out
and one to the right (Out
are being modulated by the same slow LFO. One of
the VCAs has the LFO voltage patched straight into it,
but the other has an A-175 patched in line first, so
receives the LFO voltage inverted.
LFO
Signal
In
Fig. 1: Panning
) stereo channel. Both VCAs
R
A-130
Out
A-175
A-130
Out
L
The changing state of the LFO voltages results in
corresponding changes in the perceived position of the
sound in the stereo picture.
H It’s important to set the
gain parameter
on
both VCAs to roughly halfway.
)
L
P Interesting types of panning can result if you
use a different modulator (for instance, AM,
FM, Random Voltage, S&H).
If you replace the two VCAs with two A-125
VCPs, the result is a sort of rotating stereo
phasing.
Mirroring a scale or arpeggio
The patch in Fig. 2 shows a way of using two VCOs to
create a mirror-image of a series of notes.
The pitch CV is patched directly to VCO 1, but goes
through an A-175 and is inverted before it gets to VCO
2.
H The relative pitch of VCO 2 can be controlled
with an attenuator.
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System A - 100
Dual Voltage Inverter
A-175
VCO 1
CV
A-175
CV 1
VCO 2
Fig. 2: Mirroring a series of notes
AM with control of timbre
The example in Fig. 3 shows amplitude modulation
with timbre control.
The frequencies of both the carrier VCO (VCO 1) and
the modulator VCO (VCO 2) are in the audio range.
The pitch CV from the keyboard is patched via an
A-175, and so is inverted before it controls the modulation amount (VCA 2). The result is that the sideband
harmonic distortion is stronger, the lower down the
keyboard you go (see also the user examples in the
A-130/1 manual).
CV
VCO 1
VCO 2
: AM with timbre control
Fig. 3
P
As an alternative, a free-running VCO 2 can
be used to supply the pitch CV.
You can expand this patch by adding an
A-120 VCF after VCA 1, and controlling its
cut-off frequency with the inverted pitch voltage. This has the effect of filtering out more
of the sidebands in higher notes.
VCA 1
VCA 2
Gain > 0
A-175
5
A-175
Dual Voltage Inverter
6. Patch-Sheet
System A - 100
doepfer
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.
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.
Make multiple copies of your composite diagram,
and use them for remembering good patches and
set-ups.
P • Draw in patchleads with colored
pens.
A-175
VOLT. INV.
In
In
Inv.
Out
Ctr.
-
In
In
Inv.
Out
Ctr.
-+
A-175
VOLT. INV.
In
In
Inv.
Out
Ctr.
-
In
In
Inv.
Out
Ctr.
+
-+
+
A-175
VOLT. INV.
In
In
Inv.
Out
Ctr.
-
In
In
Inv.
Out
Ctr.
-+
+
6
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