Why do my speakers "POP" when I turn off preamp?

To Jea48, that won't do any good because the turn-off (and -on, too) transient is created by the line stage, and that's always in the circuit full volume no matter where the selector switch or volume control is set.

"Next you will be telling us that you cannot pick up your lawnmover with it running and not cut off your fingers."
Just who is 'you', Thg? There are a dozen people above you.
.

Jea48,

The input impedance to an amp is quite high. Therefore, it
doesn't take much signal for the amp to see it.

If you install a shunt - or even if you try to short the
output - that shunt or short is still in parallel with the
amplifier input. [ Any "short" you place on the terminals
still has a finite resistance - so it's not a true short. ]

Even though most of the "signal" current from the shutdown
transient is sent through the shunt - a tiny amount still
finds its way to ground through the amps input stage.

Result - problem not solved.

The only safe solution here is to shutdown the amp.

Dr.Gregory Greenman
Physicist