User`s guide

10
From Pre-Amp
output
"Q" Bias Adj.
P.C.B.
4:1 8:1 12:1
20:1
4:1
8:1
12:1
20:1
Attack Time
Control
(F.P.)
Release Time
Control
To GR
Circuit
S1B
S2B S3B S4B
-10V
U3
2k
R59
5M
R56
25k
R55
C27
.022
U3
CR2
CR3
+
C21
80uf,25V
+
C23
6.8uf,35V
+
C19
6.8uf, 35V
+
50V
C20
50uf
Q10
2N3707
Q9
2N3707
Q8
2N3707
Q7
2N3707
C17
1uF
U3
U2
S1
S1A
S2A
S3A
S4A
R76
150
R75
470,1/4w
R73
560,1/4w
R68
1.5k,1/4w
T&C
R64
1.5k
R60
3.9k
R35
10k
R83
R57
270k
R54
470
R53
47k
R52
47k
R46
47k
R47
47k
R46
1k
R50
180
R49
2.4k
R48
7.68k
R43
38.3k
R42
180k
R41
270
R40
2.4k
R39
4.7k
R38
47k
R37
470k
R36
1M
R22
47k, 1/4w
R6
1k
R21
56k, 1/4w
R20
56k,1/4w
R19
68k, 1/4w
T&C
Figure 5 – 1176LN Gain Reduction Control Circuit.
Gain Reduction Control Circuit
This circuit controls the amount of compression as well as the attack and release time of the
limiter. The input to this circuit is taken from the output of the preamplifier section, just
before the volume control potentiometer (R23). The compression ratio push-button
switches determine the level of the signal which is sent to the to the sidechain. This
determines the amount of compression.
Transistor Q7 acts as a phase inverter which is followed by Q8 , an emitter follower. This
signal then feeds CR3 as well as Q9 and Q10 which comprise another phase inverter /
emitter follower combination. This is then fed to CR2. Note that the signal applied to CR2
is 180
°
out or phase with the signal at CR3. Since they are out of phase, the combination
of CR2 and CR3 act as a full-wave rectifier. The output of the rectifiers are then filtered by
C22 which smooths the signal. This DC voltage is proportional to the level of the input
signal.
A bias level is applied to the diodes by the Compression Ratio pushbutton switches. This
controls the threshold of limiting, and is adjusted for the correct value as determined by the
currently selected compression ratio selection. R55 controls the compressors attack time