Hi Colin,
First intuition is audio noise that is just higher than human hearing range
but still within the dogs hearing range. Key down, such as tuneup and CW
as you describe works the power supply transformer hard and for duration
long enough to get stuff vibrating due to the magnetic fields of the
transformer. Although the transformer vibrates at 60 hz (in the US), the
assembly may have a resonance at a (much) higher ordered harmonic.
The only suggestion I can think of at the moment to confirm this theory (and
assist in damping the vibration if correct) would be to use an extended
range microphone and display its output on an oscilloscope so that you
would be able to see noises what you can't hear. First thought for
correction would be to make sure all the fasteners on and around the
transformer are tight - would think that even small changes in fastener
tension could make, break, or alter a vibration at that frequency - so just
changing the tension of the fasteners a little might possibly help.
Mechanical vibration has similar properties to an electrical tank circuit.
Resonance is proportional to (k/m)^0.5 where k is spring rate and m is mass.
Spring rate is generally related to the mechanical stiffness of the
assembly, of which fasteners may play a part of. A mechanical system's
response at resonance can be altered by dampening (friction), which changes
the Q of the response. Techniques in reducing mechanical vibration involve
altering the resonance frequency out of the excitation range, or if not
practical, adding dampening to reduce the peak magnitude of the response.
Hope this helps & good luck.
73
Matt
KM5VI
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Colin Lamb
Sent: Wednesday, February 04, 2015 12:04 AM
To: amps@contesting.com
Subject: Re: [Amps] I'm not kidding: TL922
On 2/3/2015 8:12 PM, Dave Borcher wrote:
> Group, this is for real, I'm looking for suggestions. TL922 amp,
> fairly good condition;when I key it full power for tuneup or CW, my
> little dog goes absolutely nuts.
Parasites?
Colin K7FM
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