Need help troubleshooting Butler preamp/OD

[warro]

My old Tube Works Real Tube really needed a new paint job, so I took it apart and sent the enclosure off to be powder coated. When it came back, I reassembled everything, and now all I get is a loud hum.

This little preamp/OD is AC powered, but the hum occurs whether the unit is plugged in or not. The only difference is that the hum is much louder when the thing is plugged in. If I touch the outside of the plug on the cable that's inserted into the output jack, the hum gets quieter but does not go away.

I have tried a ground lift, and I've tried replacing both the input and output jacks. When I reassembled the pedal, I also replaced the original three-wire AC cord. I'm pretty sure I put everything back together correctly (it's a simple unit), but maybe there is something I've missed.

Any suggestions on what to look at next? FWIW, this is a non-TB circuit. The tube is new and was working fine before I took the pedal apart. Also, I'm wondering if this is a mechanical problem as opposed to a circuit issue, given that the hum occurs regardless of whether there is power.

Thanks for any suggestions.

P.S. I realize this is a pedal and not an amp, but I figure you techs here in the amp section will be very helpful.

[GearHeadFred]

EDIT: After re-reading your post, I'm not certain if you're saying the pedal is working, but has a buzz.. or if it does not work and has ONLY a buzz?

I have the same pedal and had the same problem after taking it apart!

I contacted Butler and they were helpful... even though this product has been discontinued for a long time.

I too suspected a mechanical hum.. Make sure to tighten the two screws that hold the transformer to the chassis.. This is not fix my hum.

I went so far as to install isolated jacks on the input/output.. This did not fix my hum!

I tried lifting the ground on the 3-prong cord... this did not fix my hum!

Finally I discovered that I have to lift the ground on the entire pedal board.. I do it on the power strip, and it runs dead quiet..

Ground loops are a major drag... inside or outside!

[warro]

Hmm, very interesting. My pedal gets only hum. I cannot get a signal through it. For a few minutes, the hum cleared up after I replaced the output jack. Then I replaced the input jack and the hum came back! So now it just hums. So far I have tested the unit only by itself, so there is no entire pedalboard to lift the ground on. I also clipped the ground wire on the three-wire power cord (inside the pedal) and had no luck. Sounds like this could be a real mystery.

[Trout]

Hmm, very interesting. My pedal gets only hum. I cannot get a signal through it. For a few minutes, the hum cleared up after I replaced the output jack. Then I replaced the input jack and the hum came back! So now it just hums. So far I have tested the unit only by itself, so there is no entire pedalboard to lift the ground on. I also clipped the ground wire on the three-wire power cord (inside the pedal) and had no luck. Sounds like this could be a real mystery.


Did you clean the powder coat off the box where the jacks bolt on?
Any other potential grounds to the box?

Possible the tube just pooped?

[warro]

I just swapped out the tube, and the hum persists.

I was wondering about the powder coating where the jacks are. There is indeed a coat of it on the inside of the box where the jacks mount. Do I need to clean this off? Is the powder coating preventing a necessary ground connection? If so, do I need to clean off the finish on both the inside and outside of the enclosure? Or can I just clean the inside? Or is there another option, such as running a ground wire from a jack to an unfinished part of the enclosure?

Thanks for the tip.

[Structo]

Not familiar with that pedal but a lot of pedals don't even have a ground wire to the jack.
They use the enclosure as the ground path.
So yes, clean the powder coat off where the jack contacts the case.
Also you could run a ground wire to the sleeve part of the jack.

Did you have to disconnect any wires when you took it apart?

[warro]

OK, thanks for all your help. It's working now. Not sure what I did, but it seems to have had something to do with a jack not grounding. Just as you guys suspected.

I was about to start cleaning off the powder coating (though I wasn't sure how yet) when I decided to try something else first. I loosened the input jack and jiggled it around, then retightened it. Apparently I found a sweet spot, perhaps inside the hole where the jack mounts. I did not have to clean any powder coating off after all. However, if the problem recurs, I will try that.

Structo, yes, I had to disconnect some wires. I untwisted the wire nuts on the AC power cord, and I also clipped (and later resoldered) the wires to the momentary bypass switch. Also, while this pedal did have a ground wire from the output jack to the green wire on the AC cord, I read somewhere that it's not needed. The earlier versions of this pedal had two-prong AC plugs with no ground wire. Real Tube added the ground later to comply with UL listing standards. This makes sense, as nothing changed when I clipped that green wire in an effort to stop the hum. I suppose I could reconnect it now, but I think I'll quit while I'm ahead.

Thanks again for the help.