Amp Problem - 'Breathing Speakers'

[Rob]

Sounds like somewhere perhaps there is a floating ground somewhere, or maybe
a sine wave riding on a slowly rising and falling reference. AFAIK, most
amps are AC coupled in several places, so the only thing I could think is
the amp that is directly driving the speaker has a very bad problem with a
floating ground or level. I would take alook at the output to the speaker
with a scope first, then trace back.

----- Original Message -----
From: "J. Larry Hendry" <jlarryh at iquest.net>
To: <synth-diy at node12b53.a2000.nl>
Sent: Monday, January 15, 2001 7:01 PM
Subject: Re: Amp Problem - 'Breathing Speakers'


> Very interesting. I have never seen such behavior.  I would think that the
> DC current (hard to call 2Hz AC) required to move a speaker in that
fashion
> might be thermally damaging to the speaker though.
> Larry Hendry
>
> ----- Original Message -----
> From: Vic Vector <maddock at execpc.com>
> To: <synth-diy at node12b53.a2000.nl>
> Sent: Monday, January 15, 2001 3:12 PM
> Subject: Amp Problem - 'Breathing Speakers'
>
>
> 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
>
>
> --
>
>
>
>