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VCA’s
(Voltage Controlled Amplifiers)
&
ELECTRICAL PIN-OUTS
Used in Professional Audio for some years, but totally new to the car audio world, is a remote
control gain devices called a “VCA”. This is a small integrated circuit that can control the feed-
through gain of a circuit from a remote location. It operates much like an external “hand” that
controls the signal flow through a circuit, much like a simple water flow valve.
VCA CONTROL VOLTAGE
------+
SIGNAL
INWTS
/J
I
VCA OPERATION
I-
OdB
-20
-40
K
m
THDL
-60
LIMITING
-80
-100
-100
-80
-60.
-40
-20
ode
+
CONTROL
VOLTAGE
VCA TRANSFER FUNCTION
Many people want to have a remote control for a high power amplifier in order to control the
loudness of a subwoofer amplifier independently of the radio. Remote mounting of an input gain
control would be a major problem with most car audio amplifiers because of the likely noise
intrusion into the signal path.
With a VCA circuit on the input of an amplifier, the gain can be controlled remotely but is done
with moderate level DC voltages (O-1 5 volts) that are insensitive to noise (noise is an AC voltage).
Using the optional Blaupunkt remote control (RM-1) you simply plug the remote into the amp to
control the overall gain. For people wanting to interface with highly custom installations, you can
use an RJ-11 telephone jack and variable resistor to achieve similar results using the circuit below,
This is
&
recommended for very experienced Blaupunkt installation centers for it may void the
warranty of the amplifier otherwise.
l -
REMOTE GAIN
CONTROL
ELECTRICAL
PINOUT
6
.
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