In article ,
Gareth Magennis wrote:


I've never seen a solid state relay in a Power Amp. Maybe there's a
good reason for that - AC transmission, Inductive loads, back emf etc.
A quick look at Farnell shows you don't generally get DPDT ones, so you need
2 for a stereo amp, and they are not that cheap.

SSRs which can handle reasonable-to-high currents are typically triac
designs, I believe (or possibly back-to-back SCRs in some cases). I
don't think they're going to be able to handle speaker-level audio
without introducing a great deal of noise and distortion, associated
with the switching on and off of the triac at the zero-crossing
points.

Before you try doing this "for real", try an experiment with an
external SSR first (between an amp's speaker outputs and a speaker).
Probably best to use throw-away components all around. I doubt you'll
like how it sounds.

Also, remember that a typical SSR won't switch off (open) anywhere but
at the zero crossing. If your amp's relay-drive circuit is part of a
speaker-protection circuit (to turn off the relay if DC is detected at
the output), using an SSR would defeat this protection. If an output
transistor shorts to the + or - rail, you'd end up dumping DC into
your woofer with no cutoff and probably destroy the woofer.

I'd strongly suggest using a real relay. If necessary, build a small
interposer board to convert the original relay's pinouts to those of a
high-quality commodity relay.