doepfer
+ In
- In
Comparator
+ In
- In
A-167
System A - 100
1. Introduction
Module A-167 compares analog voltages and derives a gate signal. The state of the gate output (low/
high) depends upon which of the voltages is higher.
It is possible to compare two external voltages (+In
and -In) or an external voltage (+In or -In) with a
manually adjustable value (Offset control). Both analog inputs +In and -In are equipped with an attenuator.
A LED shows the current state of the gate output.
CMP
A-167
Analog
Sum
Comp. Out
Inv. Comp. Out
Off set
Gap
The Gap control is used to adjust a so-called
"hysteresis". As long as this control is set to zero the
switching levels for both on and off state of the gate
signal are identical. As soon as the Gap control is
turned up the switching levels for on and off state fall
apart and a so-called hysteresis appears.
Normal and inverted gate outputs are available.
In addition the internal voltage a1*(+In) - a2*(-In) +
Offset is available at the Analog Sum socket. Consequently the module can be used as subtractor and
offset generator too.
1
A-167
CMP
System A - 100
doepfer
2. Overview
➊
➋
➌
➄
➍
➀
➁
➂
➃
➎
Controls:
1 + IN : Attenuator for voltage at input !
2 - IN : Attenuator for voltage at input "
3 Offs. : Offset control
4 Gap : Control to adjust the hysteresis
5 Comp. Function : Gate indicator (LED)
In- / Outputs:
! + In : Non-inverting voltage input
" - IN : Inverting voltage input
§ Analog Sum : Analog voltage output, makes
available the internal voltage:
a1*(+In) - a2*(-In) + Offset
$ Cmp. Out : Gate output
% Inv. Cmp. Out : Inverted gate output
2
doepfer
System A - 100
CMP
A-167
3. Basic principle
The module generates internally the voltage U
U
= a1 • In+ - a2 • In- + Offset
SUM
The factors a
of the inputs In
the resulting voltage U
U
U
The internal voltage U
and a2 represent the manual attenuators
1
+
und In-. According to the sign (+/-) of
the gate output is activated:
SUM
> 0 : Gate = "high" (~ +10V)
SUM
≤ 0 : Gate = "low" (~ 0V)
SUM
is available at the socket §.
SUM
Consequently the module can be used to attenuate
and subtract analog voltages and to add a fixed offset
voltage to a voltage (similar to one of the sub-units of
the Attenuator/Offset Generator A-129-3).
The Gap control 4 is used to adjust the so-called
"hysteresis" voltage. As long as this control is set to
zero the switching levels for both on and off state of the
gate signal are identical. As the Gap control is turned
up the switching levels for on and off state fall apart
and a so-called hysteresis appears. In this case after a
state change of the gate output the internal voltage
has to vary at the hysteresis amount before the
U
SUM
gate state will change back.
SUM
:
Fig. 1 illustrates the Gap resp. hysteresis function by
means of a triangle LFO input signal.
Input Signal
(LFO T r iang le)
Comparator
Level
Comparator
Output
(gap = 0)
Comparator
Output
(gap > 0)
Hyst er esis
Fig. 1: Effect of the Gap control on the gate signal
3
A-167
CMP
System A - 100
doepfer
4. Controls
1 + In • 2 - In
The controls 1 and 2 are the attenuators for the
voltages fed to the sockets ! resp. ".
3 Offs.
This control adds a manually adjustable Offset voltage, i.e. a fixed value is added to the internally calcu-
lated voltage difference a
offset range is approximately -10 V (fully counterclockwise) to +10 V (fully clockwise). In the middle position
the offset is approximately 0 V.
If only one of the inputs is used the module works as
an offset generator (and attenuator); the attenuated
and - if input " is used - inverted voltage with offset is
available at the Analog Sum socket § (see fig. 2 and
chapter 6).
4 Gap
This control is used to adjust the hysteresis (see
chapter 3 for details).
• In+ - a2 • In-. The adjustable
1
Original
Signal
U =
SUM
+ In + Offset
Gate
U =
SUM
- In + Off set
Gate
Off set
Off set
Fig. 2: A-167 as attenuator / offset generator
5 Comp. Function
LED 5 lights up if the internal voltage U
(> 0V) and consequently the Gate output is "high" (~
+10V).
is positive
SUM
4
doepfer
System A - 100
CMP
A-167
5. In - / Outputs
! + IN
The input signal fed into this socket is attenuated with
control 1 and added to the internal voltage (U
" - IN
The input signal fed into this socket is attenuated with
control 2 and subtracted from the internal voltage
).
(U
SUM
§ Analog Sum
At this socket the internal voltage U
(see chapter 3).
is available
SUM
$ Cmp. Out • % Inv. Cmp. Out
The Gate output $ is "high" (~ +10V) if the internal
voltage U
The inverted Gate output % always has the opposite
state of the normal gate output $. Consequently this
output is "low" if the internal voltage U
Otherwise it is "high".
is positive. Otherwise it is "low" (~ 0V).
SUM
SUM
).
SUM
is positive.
6. User examples
The main application of module A-167 is the generation of gate signals depending upon analog voltages, e.g. a gate signal that depends upon the present
value of a LFO (triangle), ADSR or random signal can
be generated and used to control a voltage controlled
switch that on the other hand switches different control
voltages or audio signals. More examples shows the
following table:
Signal
at + In
Signal
at - In
Offset
•
•
•
•
••
••
Meaning concerning
at §
U
SUM
(positive) offset generator
> 0
(negative) offset generator
< 0
(positive) inverting offset
> 0
generator
(negative) inverting offset
< 0
generator
0 subtractor
> 0 subtractor + (positive) off-
set generator
••
< 0 subtractor + (negative) off-
set generator
5
A-167
CMP
System A - 100
doepfer
The module can even be used to add the free-running
mode to each ADSR (e.g. A-140 or A-141) similar to a
LFO but with separate controls for rising and falling
edge and exponential waveforms - in contrast to the
linear waveforms of a LFO.
In the patch of fig. 3 the ADSR-LFO is gated by means
of the gate input of the A-140 (e.g. with another LFO or
a gate signal controlled by a keyboard or MIDI interface). This means that the "ADRS-LFO" oscillates only
as long as the gate input of the A-140 is "high". The
waveform and frequency of the ADSR-LFO is determined by the controls Attack, Decay, Sustain and Release of the A-140, and Offset and +In of the A-167.
The Gap setting of the A-167 is irrelevant.
Only certain control settings lead to an "ADSR-
H
LFO" (especially Offset, +In and Sustain) !
The patch in fig. 4 shows another ADSR-LFO. Waveform and frequency are deterrmined by the parameters Attack and Release of the A-140, and Offset, Gap
and +In of the A-167. Decay and Release of the A-140
are irrelevant.
Gate Control
Gate
A-140
ADSR
Attack
Retri gger
Deca y
Output
Sustain
Release
Fig. 3: ADSR-LFO 1
Gate
A-140
ADSR
Output
Release
Attack
+ In
+ In
A-167
Compa rato r
+ In
Inv . Com p. Out
Compa rato r
+ In
Inv . Comp . Out
Off set
A-167
Off set
Gap
Even in this patch only certain control settings
H
lead to an "ADSR-LFO" (Offset, +In and Gap) !
6
Fig. 4: ADSR-LFO 2
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