I agree with Jan, lets see your circuit!!! I tweaked an amplifier in the lt switcher cad that I designed the soldering way (about 10 years ago) just using the models I got from the yahoo switcher cad group and common sense substitution and I found it to be very accurate at a higher level, for feedback tweaking and instability, and heating. Just changing a few (about 6 values) and I totally transformed the sound (for the better). I was not looking in to noise however, are you using feedback? If not, maybe just regulate the psu rails…. The chaps on sci.electronics.design would probably give you a few opinions, quite a few *experts* live in there. LTSpice group is good too.
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