Operation Usingyour Own Potentiometer Or An; External 10 Vdc Variable Source; Troubleshooting - Crown VCA-MC4A Operation Manual

VCA-MC Series Amplifier Accessories
4.2 Operation Using Your Own Potentiometer or an External 10VDC Variable
Source
1. Turn the amplifier's back panel attenuator fully counterclockwise (off).
2. Unplug the connections to the VCA-MC module if they have been previously installed.
Remember that each connector has two channels on it. Don't unplug the VCA control
for a channel that is in use, because full volume will be sent to that zone since
the VCA attenuation is 0dB when nothing is connected!
3. Turn on your audio source. Set its output level to the maximum value you expect to use it
at. You should not hear any sound yet.
4. Slowly turn the amplifier attenuator clockwise until the system's volume is at the maxi-
mum value you want it to operate at. (Remember to refer to the power rating of the speak-
ers.) If the sound from your speakers is distorted within the first several detents, consider
decreasing the output level of your audio source.
5. The volume limit of the system is now set. This volume limit is relative to the input level
you just used to set it. If the input level from the audio source increases, so will the output
level of the amplifier. The volume limit is not an absolute limiter.
6. Turn off the amplifier.
7. Plug the VCA control (potentiometer or independent 0-10V DC source) into the VCA-MC
module.
8. Turn the amplifier on.
Using the potentiometer or the DC supply control, set the supply voltage to achieve the
desired attenuation according to the equation below:
Vc = Attn (dB) / (–7)
[Vc is the dc control voltage; Attn (dB) is the attenuation in decibels.]
0 VDC results in no attenuation (0 dB).
10 VDC results in full attenuation (–70 dB).

4.2.1 Troubleshooting

If the amplifier volume does not respond to the external DC supply, a miswire is suspect.
Check the pinout at both ends of the cable. Check that the +10V and ground connections are
made properly. If you are using an external 10VDC variable supply, make sure that the sup-
ply is switched on and is wired to the correct channel's VCA control input (VCA1, VCA2,
etc.). If you are using your own potentiometer, check that it is wired as in Figure 3.2.
If the operation of the VCA control is inverted (i.e., full volume when the control is fully
counterclockwise), check the VCA control wiring (refer to Section 3).
Operation Manual
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