Going crazy with hum free ABY and transformer isolation

[andresbianco]

Hello all,

I'm designing a 2 amps to 2 speakers switcher (to select one amp with one or the other speaker). I'm doing all the logic with relays and precise switching (time on and off ) in order to avoid no-load situation when switching between (tube) amps.




Anyway, ground loops may occur of course. I suppose when sending to amps and also in the returning path from amp's speaker outputs (if some of the poles are connected to ground).
Hope you could help me to figure this out. what I mean is, of course I can switch both , hot and grounds, to avoid interconnection between amp's grounds but that doubles relay count.

Isolation transformer could solve the sending to amp in, but what about amp out?

Thanks!

PS: R.G. I was watching your splitter design, I have a doubt about frequency response of 42TM018, from 300Hz to 3,4kHz?? do you compensate that in any way? thanks

[wavley]

PS: R.G. I was watching your splitter design, I have a doubt about frequency response of 42TM018, from 300Hz to 3,4kHz?? do you compensate that in any way? thanks

It's being actively driven so it extends the frequency response enough to be perfectly fine with a guitar, may or may not be low enough for a bass or baritone, the $6 Edcor transformer worked for me when it comes to bass guitar, but at the expense of being 4 times the size, if I just played guitar I would have stuck with the RG spec'd transformer.

[karbomusic]

the $6 Edcor transformer worked for me when it comes to bass guitar

It's a great transformer, I have a couple of them but it's Achilles' heel is no MU metal shielding so it can and will pickup any hum in the immediate vicinity. That's how I learned why some are so expensive.