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Old 27th January 2004, 07:35 AM   #11
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Join Date: Sep 2002
Location: Oregon, USA
Hmm... that's going to be tight - I looked at my layout, and it'll be relatively easy to do for one channel, but quite a bit harder for the other.

Things are looking better now. I added a feedback resistor to the inverting input and another resistor from there to ground. Put a cap across teh feedback resistor. Turned out to be too big, killed teh treble (this is the one cap in my stash that I don't know the value for), I'll pick up appropriate caps tomorrow I think. Anyway, those reduced the oscillations but didn't eliminate it. Finally I used another suggestion from the app note (which the kit instructions also had) and increased the input series before the first preamp to 2K ohms. Apparently this reduces the overall slew rate of the system. Anyway, that took care of pretty much all the oscillation. The output is still kinda fuzzy, but I'm down on the lowest setting on the voltage and the timebase on my scope, so I can't reliably make any judgement calls any more.

I can't hear any high pitched squeal from the speakers (I can if I remove the caps, but it's very low, and the scope shows a little oscillation with the cap removed). So right now I have the cap out, I'll put in caps of the correct size tomorrow.
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Old 27th January 2004, 01:56 PM   #12
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Join Date: Sep 2002
Location: Oregon, USA
I shouldn't post after midnight. Did I get that right? This cap should form a low pass filter, so to push the corner frequency up higher, I'll need to reduce the value of the cap. Correct?
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