Doepfer A-119 User Manual
doepfer
Asym.
In
A-119
Ext. In.
System A - 100
1. Introduction
Module A-119 (External Input / Envelope Follower)
is designed to allow external audio signals to be
integrated into the System A-100. It comprises a pre-
amp, envelope follower, and comparator.
Ext. Input / Envelope Follower
A-119
Symm. In
Audio
Out
Envelope
Out
Gate
Out
Gain
OverLoad
Threshold
The pre-amp has two inputs: an unbalanced input for
line level signals, with a gain factor of from 0 to 20, and
a balanced input with a gain factor of from 0 to 500,
for insertion of low level signals, for instance from a
microphone or electric guitar.
The Envelope Follower reads the signal level of the
input, and puts out a proportional voltage as an envelope at its own output (see chapter 3. How it works).
The comparator generates a gate signal whenever the
input goes above an adjustable trigger threshold (see
chapter 3. How it works).
Three LEDs help you keep track of overload, the
envelope, and the gate signal.
1
A-119
Ext. Input / Envelope Follower
System A - 100
doepfer
2. A-119 - Overview
A-119
Ext. Input / Env. Follower
Asym. In
➊
Audio Out
➌
➍
Envelope
Out
➎
Gate Out
➏
Ext. In.
0
0
Symm.
In
10
OverLoad
Thres.
10
Gain
➋
➀
➁
➂
➃
➄
Controls and indicators:
1
Over-Load : LED overload warning
2
3 LED : Envelope level indicator at (output %)
4
Thres. : Trigger threshold control
5
: Control for input signal level
Gain
: Gate indicator (output &)
LED
In / Outputs:
! Asym. In : Unbalanced input for line-level audio
Symm. In
"
Audio Out
§
Audio Out : ditto, linked with output
$
% Env. Out : Envelope output
Gate Out
&
: Balanced input for mic or instrument-
level signals (6.3 mm jack socket)
: Output for pre-amped audio signal
§
: Gate output
2
doepfer
System A - 100
Ext. Input / Envelope Follower
A-119
3. The Envelope Follower: how it works
The external audio signal (see Fig. 1a) is patched into
input ! or ", depending on its level. It is amplified by
an amount set by the gain control 1, brought up to
A-100 internal operating level, and can then be output
from audio outs § and/or $.
To produce envelope and gate signals, the amplified
signal is put through a full-wave rectifier, so that the
internal signal output has only positive voltages (see
Fig. 1b).
Next, the rectified signal passes through a 50 Hz low
pass filter, and is sent to envelope output %.
H With input frequencies of less than 50 Hz,
patch the envelope output % into an A-170
slew limiter, set to a time constant of greater
than 20 ms, to avoid remnants of the signal
being audible in the envelope.
The signal at the envelope output is compared with the adjustable trigger threshold (T in
Fig. 1c), to produce gate signals, available at
output &.
a
0
b
0
c
T
0
d
0
: The envelope follower: how it works
Fig. 1
3
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