Amp Problem - 'Breathing Speakers'

[Goddard, Duncan]

>>>I have seen that before. It turned out to be the DC component of an
> ultrasonic oscillation. The DC component changed as the waveform went
> through a distortion cycle. In that case it was cased by the crossover
> capacitor of a pizo tweeter causing some kind of tank circuit at 22Khz.
> Removing the cap solved the problem.
> > 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.<<<
> 
> 
I remember seeing this on a class-A valve amp when I was very young; my dad had this williamson amp driving a 15" tannoy (a dual concentric job) which wasn't covered with a grille or anything, and we could see the cone slowly going in and out, with the excursion being on the verge of alarming. he described it as "breathing".
as I recall, it was attributed to low frequency parasitic oscillation, caused by trying to power "one more bottle" off the same transformer, to run a pre-amp......

d.


***************************************************************************
CONFIDENTIALITY NOTICE

The contents of this e-mail are confidential to the ordinary user
of the e-mail address to which it was addressed, and may also
be privileged.  If you are not the addressee of this e-mail you may 
not copy, forward, disclose or otherwise use it or any part of it
in any form whatsoever.
If you have received this e-mail in error, please e-mail the sender
by replying to this message.

MTV reserves the right to monitor e-mail communications from
external/internal sources for the purposes of ensuring correct 
and appropriate use of MTV communication equipment.

MTV Networks Europe
****************************************************************************