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I just finished a Vibro Champ build and it works and sounds fine until you crank it up. Then, along with the nice tube overdrive there is a loud crackle. It almost sounds like a blown speaker, but I ruled out the speaker using a different speaker in a separate cabinet, I've also changed out all the tubes except the rectifier tube. The voltages are a little on the high side, but I've encountered this on friends' Champs and they sounded great. Regardless, I'm waiting on some power resistors to bring the B+ down a little. I've built several small amps over the years, but I've never had this particular problem. I'll try reflowing all the solder joints tomorrow, but I'd love to hear some suggestions from anyone who may have had this problem before. I'm also wondering if it could be the cheap output transformer I used (less than $20 from CE Distributing). Thanks in advance for your input.
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Sometimes oscillation will manifest itself as crackling. The single ended transformers see to be more prone to have the phasing reversed, especially cheaper ones.
Since you are already wondering about the OT, you might want to try flipping the phase of the primary connections.Originally posted by Enzo
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Is the crackling a 'low frequency note' issue?Comment
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Yes, the lower notes seem to be what elicits the crackle.Originally posted by Jazz P Bass View PostComment
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Since I suspected the OT and because I'm driving a 10" speaker, I installed a slightly larger OT (from SF a Fender Princeton). But the crackle is still there when the amp volume gets up around 7 - 8 and above.Originally posted by g1 View PostComment
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You could try lowering the value of V1 cathode bypass capacitor.Comment
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Update: I've just discovered that when I turn off the tremolo (shunt), the nasty crackling goes away. The plot thickens. :-(
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Schematic?- Own Opinions Only -Comment
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