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Whoop, hang on, I think I found it...
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No, never mind. It's still there. Instantaneous fizz moment when you get to about 7 or 8 on the volume.Comment
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Wait, hang on again...something else just occurred to me...Comment
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Alright, no dice. I give up.Comment
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Something I just noticed, this fizz is only present at a certain level of output. For instance, if I have the tone controls set where I like them, there's a bit of fizz with the note attack starting at 7 on the volume, but everything is fine from 8 up. Or, with the volume down, it will show up for a bit as you increase the treble, but then, after a certain level...poof. Gone. It's driving me crazy.Comment
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Wild guesses: bad tube, arcing resistors, humidity in resistors, cold solder joint.Comment
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Tried everything and never could find it. So I did what any sensible person would do. I tore the whole thing apart, bought new resistors, and rebuilt it point to point. I've learned so much in a month that it's just silly. Voltages were dead on when I fired it up and the fizz is gone, whatever it was. Sounds like a million bucks now. Now time to move on to project two. Thanks everyone. I'm sure I'll be back with more D.A. questions as soon as I get started.Comment
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Glad you solved it. Micro-arc'ing inside resistors often cause AM-like noise, as if the amp is a receiving radio. It's hard to track down, you need to isolate stages and so on. Also, carbon comp resistors are noisy when humid, which also requires isolating stages.
Believe it or not, I've quieted an amp with a hot air gun, by drying the resistors. Rebuilding the amp is a good tactic as well, though more expensive than just isolating the problem and finding the one buggy component, bad solder joint, etc.Comment
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