On 31/08/2014 2:44 AM, Cursitor Doom wrote:
Hi all,

I'm using an old Advance AF generator (15hz-50khz) in an attempt to
discover what kind of distortion my Technics hifi amplifier is
producing so I can fix it. However, for some reason I'm getting
terrible self-oscillation from the otherwise stable (though
not-very-nice-sounding) amp that can't be stopped once it starts. I'm
just wondering if I should be using some sort of buffer between the
generator and the amp input? At the moment I'm just feeing it direct.
It's the only cause I can think of. I've checked the generator by
itself on a suitable scope and it's absolutely rock solid right across
the range and the attenuators are fine so it can't be the gennie
itself; must be something I'm doing wrong. What doesn't help much is
the gennie doesn't state what its output impedance is. Not sure if
that's relevant or not, though.
Any suggestions?
cheers, cd


**It's highly likely that you are doing something seriously wrong.
Domestic amplifiers, from major manufacturers are usually VERY stable.
Here's what you should do:

0) Check to see if the amp uses bridged outputs. If so, then only test
one channel at a time and ensure that your 'scope is ungrounded, or you
are using a differential input (if available).
1) Connect your amp to a pair of isolated dummy loads.
2) Switch on. Obsrve if there is an oscillation. If no oscillation, move
to step 3.
3) Connect your sig gen and test as normal.
4) Report.




--
Trevor Wilson www.rageaudio.com.au