Amp Problem - 'Breathing Speakers'

[Vic Vector]

Here's a peculiar problem with an old Hafler amplifier that my friend
mentioned to me.. perhaps someone has seen this type of symptom before.
I can't find any similar experiences on usenet, etc.

There's a fault somewhere in this amp that causes the speakers to 'breathe' 
at about 2-3 cycles per minute. The voice coil of the speaker (any speaker,
the Hafler is just a head unit) will slowly and steadily drift from fully
impelled to fully expelled at a very regular rate (2-3cpm).

It's as if something is injecting a sine signal into the power stage of the
amplifier and passing straight current to the speaker coils. This occurs
in both l+r, l only (bridged mono) and right outputs, with no input to the 
amp.

I thought it was peculiar and people might find it an intriguing problem.

The capacitors used in the power stage of the amp are cylindrical _film_
caps, and they both tested OK.

-maddock


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