Thread: mu feedback
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Alex Alex is offline
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Default mu feedback


"flipper" wrote in message
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On Fri, 19 Mar 2010 22:45:00 -0700, "Alex"

This has been quite useful because it got me to rethinking about what
I'd done. One of the initial problems was motor boating and I
attributed that to C5, needed to block bias voltage, but now I'm
wondering about that A- B- bias string (shown in the battery
eliminator). I mean, they're all under the same filter cap and will
shift together. Sounds to me like a feedback path.

I suppose I could put multiple caps in to break up the synchrony or,
maybe better, use series diodes for the first few stages to make that
bias 'fixed'.

Whatcha think?


Motorboating is low frequency positive feedback. Typically through power
supply.
I think in your case C5 in the amp circuit has nothing to do with it -- time
constant is soooo large. But if you have concerns -- incerase it further to
2.2...3.3uF. IMO this increase will not anything significant.

Most likely the motorboating is caused by C6 in the power supply unit.
Increase it to 470...1000uF.

Regards,
Alex