Premier Rock Forum

Artifacts of class AB biasing perhaps?

I think some clarification needs to be made as to what "asymmetry" is in distortion, and what would happen to an amp with a borken* tube.First, if one 6L6 in a Quad Reverb was dead or pulled, then you'd just have less power being produced by one side of the push/pull, and I think just lower output on every other wave cycle. I think in theory it would be like a tremolo effect except the volume cut wouldnt be significant enough to be noticeable, and the frequency would be too high to be noticeable. That's NOT what "asymmetrical" distortion or clipping usually refers to. With asymmetrical clipping one side of the wave is being clipped more or differently than the other. In an amp with a pulled tube, as described, any clipping should be the same on either side of the wave. I dont really see how an amp with a tube removed could or would generate different distortion than one running normally. There is the possibility that something ELSE in the amp had failed and produced uneven distortion but that could be any number of things.*I caught this typo, but decided to leave it as-is. Sue me.

TylerSavage wrote:Dr Tony Balls wrote:I think some clarification needs to be made as to what "asymmetry" is in distortion, and what would happen to an amp with a borken* tube.First, if one 6L6 in a Quad Reverb was dead or pulled, then you'd just have less power being produced by one side of the push/pull, and I think just lower output on every other wave cycle. I think in theory it would be like a tremolo effect except the volume cut wouldnt be significant enough to be noticeable, and the frequency would be too high to be noticeable. That's NOT what "asymmetrical" distortion or clipping usually refers to. With asymmetrical clipping one side of the wave is being clipped more or differently than the other. In an amp with a pulled tube, as described, any clipping should be the same on either side of the wave. I dont really see how an amp with a tube removed could or would generate different distortion than one running normally. There is the possibility that something ELSE in the amp had failed and produced uneven distortion but that could be any number of things.*I caught this typo, but decided to leave it as-is. Sue me.I would think having only 1 tube running out of a quad, you're going to have a totally different impedance - no longer running matched to the speaker load, would be a totally different sound as wellWell yeah, but its still not gonna create an asymmetrical distortion.

https://www.youtube.com/watch?v=MrWamIxoZ2where's a rawer track with less doublingi have a turbo rat, still sounds different but i guess i'll stick with itthanks

I ve gotten a sound like is being described here, but it was with a 12 string Strat, a Hotcake, and a Super Reverb that was about to need some expensive transformers replaced. It did sound cool but you absolutely had to have a pedal on to get any sound of it. I remember the blues dude in the practice space across the hall became very interested in what I was plugged into all the sudden. Take that how you will!

This is the most technical and scientific exploration of Nirvana I've ever seen.That's all. Good stuff guys.

This is all a ruse. It was an HP-1 Harmonic Percolator all along...

FWIW the amp in question had literally one working 6L6 of the original quad, so only one side of the output transformer was being driven, the load on the phase splitter was asymmetrical and who the fuck knows what happens with the feedback tap, not me. The sound with no pedals or overdrive was a broken, thin sound that may be familiar to owners of faulty Fender equipment. That's why I've always referred to it as asymmetrical.Consider the case of a single-ended single-tube amplifier driven into distortion. As the tube tries to deliver more voltage and current, eventually the upward excursion exceeds the capability of the tube and starts to square off into clipping, whether at the tube itself or by first saturating the transformer. The downward excursion drops tending toward ground, and there's not really a mechanism where that excursion can clip in the same way. I would think a single tube trying to drive half of a push-pull circuit would behave that way, but that's me just guessing.

If someone asked me to listen to that song and try and get a guitar tone like it (without all the other context of how they did it originally) I would start by1. Running a preamp pedal into some slight distortion, maybe with some slightly boosted highs2. Run that into a tube amp that without the pedal is still breaking up slightly (then turn the pedal back on)

If it ain't borken, don't fix it.