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V-Twin pedal trouble

Posted: Sat Jan 19, 2019 1:18 am
by mtglick
Hi, all--newbie with a repair question.

A few years back I picked up a used V-Twin pedal, and used it exclusively as a front-of-amp pedal, guitar in and guitar amp out (this unit has multiple line outs, one for instrument level, one for power amp level, and one for heaphone/mixer level). I knew the pedal had these other features but never actually used or tested them.

Recently, I tried to set it up as a headphone amp, but couldn't get it to work, just got a ground hum. Then I realized that I'd never tried to run the pedal as anything other than straight into a guitar amp, and got very nervous that somebody had stuffed a distortion circuit into a shell and sold it. So I opened it up, and fortunately the interior was as expected. However, I'm still experiencing the hum issue, on both the headphone out and power amp out. Everything looked clean inside, no obvious circuit faults, blown caps, etc.

The basic behavior is the same on both the power amp out and the headphone out, other than the headphone/mixer switch does affect the headphone output, when I toggle the switch to Headphones, I get stereo hum, if it's in Mixer, I get mono hum. The hum intensity changes with the channel as well, Solo is different from Blues. The hum on the clean channel sounds closer to the Solo channel, but again, it's just hum. No signal from the guitar at all.

All that said, the instrument level output seems to work just fine--no hum, no major issues, all the knobs work as they should, sounds good. It's just the alternate levels out that have failed.

I have a very basic understanding of electronics, and a diagram ( that seems to generally match up with the pedal's configuration. What I'm hoping is that someone can point me in the right direction. I recently replaced the power supply with a new one from the Mesa-approved supplier (Mesa no longer makes this power supply), and that had no effect. I've tried multiple tubes in both positions, and while they do have an effect on the sound, it's the expected effect for the tube type and they work fine with the guitar, so that's not the problem either. My best guess is that something in output stage of the the pedal fried, but I don't know what. I can solder tolerably well, so I'm not afraid of swapping components, but this isn't your ordinary fuzz box--there are a LOT of parts in this sucker and it would take me another three or four years to shotgun my way through it.

Does anyone have any guidance on what could have caused this particular failure, or ideally where I could start replacing (or testing with a multimeter) components?

Thanks mucH!

Re: V-Twin pedal trouble

Posted: Tue Feb 19, 2019 3:23 am
Hey there,

mine did the same, the last operational amplifier in the chain was broken and had to be replaced... not an easy task. Good luck!