Switching Question-speaker selector

[Sleeper]

I have a plan, but I don't know if this will really work as I'm thinking it will.

here's the signal chain.

<all balanced sources (driven by a variety of buffers based on DRV134, opa2604, transformers etc.) >

<Through a stereo balanced bridged-t attenuator>

<SWITCH (for speaker selection source to either A,B, OR,C (never AND))>

<unknown power amplifier inputs-possibly servo balanced or just differential, or at some point perhaps a transformer>

I'm pretty sure I can just switch the hot+pos and leave the hot+pos floating on the amplifers that are not selected

I'm concerned that if I switch BOTH hot+pos AND cold-neg
I'll have the power amplifiers completly floating in such a way that they will hum badly.

If I were to switch BOTH hot+pos AND cold-neg I think I would have to shunt the unused speakers to ground, but so far I haven't come up with a switching diagram for this that actually will work.

Any thoughts or advice would be much appreciated.
Sleeper

 

[bcarso]

"I'll have the power amplifiers completly floating in such a way that they will hum badly."

You mean they are tube amps? In that case I would provide a dummy load, or make sure you don't drive them when unselected. If they are solid state they won't care about having no load.

 

[Sleeper]

Hi bcarso
yeah a dummy load. like me. I know too much for my own good and not enough to do me any good.

im using terminal strip outs so it's easy to jump a resistor(s) into the circuit if it hums.

so if it does hum I should add

Opt #1 a resistor from hot to cold

OR

opt# 2 resistor from hot to ground
AND
resistor from cold to ground

looking at h. tremaine's "passive audio design", I think # 2 would be the way to go. what do you think.

 

[PRR]

I'd just have one power-amp, and switch the speaker lines.

If you must have multiple amps: first, try it. Cut the end off a cable, plug it into the amp input, and put the other end where your proposed switch will be. Good balanced inputs won't buzz, though they may pick up radio.

If you don't break both wires, most inputs will leak a little signal.

If you must terminate, put a short or, if possible, a 100Ω resistor across the input. This does complicate the switching.

 

[Sleeper]

Thanks for the advice gents.
Yeah, I was afraid I'd have to switch both. Typically I thought I had all my parts in order but I'm one switch short.
Should have bought a sixpack.
:sam:

Sleeper