On Wed, 27 Apr 2016 18:44:59 -0700 (PDT), Phil Allison
wrote:

Dave Plowman (Nutcase) wrote:

Pretty basic MOSFET power amp.

I'm used to it thumping at switch on. No speaker relay in this basic
design.


** You posted the same here in December last year.


But one of them as taken to thumping at switch off. Not always, which
makes fault finding more tricky.

Most likely cause?


** Old and bad electros are the cause of almost everything.


BTW; anyone familiar with the famous Crown DC300A ?

Both channels would emit a long squeal about 10 seconds after switch off - it sounded much like a party balloon being let down while squeezing the neck.

There was a note inserted in later service manuals that *no attempt* should be made to fix the problem, as any possible fix would render the amp unstable.




.... Phil

So they had an instability they couldn't fix, but sales took it off
the engineers and put it in the market anyway? Why am I not
surprised?

I don't know the design, but assuming it is an op-amp (as most audio
amps are) it shouldn't be beyond the wit of man to get a dominant pole
into the loop.

d

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