A/B testing switch

[jimbo1968]

I'm going to build a switching box for speaker and amp comparisons.

I could do a simple 2 directional system. In one direction it will switch one amp between 2 speakers, in the other direction it will switch 2 amps into 1 speaker.

But I have some questions.

For amp testing, is it overkill to switch between speaker and a dummy load to keep the other amp working ?

I saw an amp switching box described somewhere that commoned the -ve terminals. Is that safe for all amplifier designs?

[Nigel Goodwin]

Originally posted by jimbo1968
I'm going to build a switching box for speaker and amp comparisons.

I could do a simple 2 directional system. In one direction it will switch one amp between 2 speakers, in the other direction it will switch 2 amps into 1 speaker.

But I have some questions.

For amp testing, is it overkill to switch between speaker and a dummy load to keep the other amp working ?

Yes it's overkill, there's no need to use a dummy load on a transistor amlifier, however a valve amp must not be used without a load.

I saw an amp switching box described somewhere that commoned the -ve terminals. Is that safe for all amplifier designs?

It's NOT safe for bridged amplifiers, and will damage it, so I would suggest switching both to be safe.

[jimbo1968]

Pretty simple then.

DPCO (dual pole changeover)
30V, 8A

should do the job ?

[jimbo1968]

just realised, I don't know how relays work.

does a changeover relay latch in either direction and you apply a burst of either +v or -V to choose which way it is switched ?

[Nigel Goodwin]

Originally posted by jimbo1968
just realised, I don't know how relays work.

does a changeover relay latch in either direction and you apply a burst of either +v or -V to choose which way it is switched ?

No, it's one way without power, and the other way with power. Although you can buy special latching relays.

[jimbo1968]

I've just worked out than I will get plenty of hours testing from a set of rechargeable batteries, so that's no problem.