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Original Message

We went down this road about 30 years ago.

Posted by Ralph on July 10, 2017 at 10:29:39:
If I have this right, I suspect that you are not wanting to install a protection relay.

The problem of course is that if the relay shorts the output to ground, the servo can't detect the output voltage. So that's a non-starter.

The other way is to put the contact of the relay in series with the output signal, meaning that the signal has to go through the relay contacts. And that the amp has an open input until the preamp stabilizes.

Obviously you need a mute circuit as well as relay protection (mute circuit shorting the output while the relay disconnects the preamp from the output until the DC offset is 0volts). Even if the preamp only makes -2 volts for a short time, that is enough to damage some loudspeakers if the amp passes that with gain. Most amps have protection circuits that trip with such input conditions, but you can't count on that! So the preamp has to not be able to damage the amp or speaker, plain and simple.