I have a Vox AC10c1 on the bench and was surprised that the amp's clipping waveform looked terrible. I would think that a small wattage amp would be designed to drive into saturation so I don't know if this is normal for this amp or there is an underlying issue.
The tubes test strong. To me, it looks like some sort of frequency doubling, possibly in the long tailed pair phase inverter?
Here is a picture and a link to the service manual: http://dealers.korgusa.com/svcfiles/AC10C1_SManual.pdf
The tubes test strong. To me, it looks like some sort of frequency doubling, possibly in the long tailed pair phase inverter?
Here is a picture and a link to the service manual: http://dealers.korgusa.com/svcfiles/AC10C1_SManual.pdf
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This is the loudspeaker end. It was late and I didn't start looking at the output tube grids coming from phase inverter. Or it could even be the phase inverter itself being over driven. The waveform gets even uglier when you turn the master volume down.
I could be wrong, but I would think if it was the output transformer saturating it would do it on both peaks no? It seems to me half the waveform is messed up which is what is leading me to the phase inverter.
The amp sounds horrible when turned up is the complaint from the customer so it is not what the musician wants sound wise. I haven't plugged a git-fiddle in yet but when I was doing my normal bench testing I check output power and since it's a guitar amp I check what it does when overdriven, which this looked ugly, and from experience should sound ugly too.
I don't see too many of these little Vox amps, actually I can't remember if I have ever had one on my bench so I have no reference to what they should sound like or perform. I am hoping someone can chime in with some experience with them and either say it's just a design flaw inherent in these amps or something else is wrong.
Till then, I'll keep poking around and see if I can make it better that way there is some technical reference to these on the internet and if someone else wants to make these amps sound better they'll know how to do it.
On a side note, the owner said it has always sounded like that since he has owned it and he kind of though it was the speaker or something he could upgrade. It's certainly not the speaker, this was taken on a non inductive resistive load.
Merlin alludes to this being possible with a long tailed pair but he doesn't tell why, it's mainly an issue with cathodyne phase inverters.
The Valve Wizard
Check out the bottom of the page where it shows the waveform of frequency doubling. Merlin says it's caused by grid current flowing through Rk and raising the voltage at the cathode.
The Valve Wizard
Check out the bottom of the page where it shows the waveform of frequency doubling. Merlin says it's caused by grid current flowing through Rk and raising the voltage at the cathode.
Thanks I will check them. That schematic you linked is for the original AC10 which was a much better amp this the current production one on my bench, the "AC10-C1" which is a hybrid amp. I linked a schematic to the service manual in my first post.
All your fans watching you on their 'scopes will be revolted.
Or not? How does it SOUND when flogged brutally?
The LTP "can" be scaled not to grossly overdrive the outputs. Here it looks like 35V peak up-swing on 11V power grids- it DOES exceed gross overdrive.
I suspect it adds a small extra harmonic excitement at the extreme.
If it isn't nice, don't play that hard.
If you want more Fender 6L6 like tones, increase the 2K dropper to the LTP, feed much less local B+. May have to go to 100V to get "polite" clipping.
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