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Sorry to double post this, but I realized that my original title (Distortion in the FX Loop) was misleading. My guess is most people read that title as I wanted to run a distortion pedal in the loop, where that is not the case.
I have not been able to figure out how to change the title or delete my previous post, so I an admin could delete it I would appreciate it. I've reposted my original post, with a few additions/changes, below:
So I'm trying to figure out why I started getting distortion when the FX loop of my B-52 AT100 is engaged. This started, or at least I first noticed, it at band rehearsal last week when I started playing the intro to Wish You Where Here. I was using the clean channel as usual, but it was not so clean. Not heavily distorted, but more of a smooth overdrive. It's vert touch sensitive. The harder I play, the more the distortion.
After rehearsal I tried to figure out where it was coming from. I narrowed it down to when the FX loop is engaged, which for me is pretty much always.
It's a tube FX loop so I swapped that tube out with a known good tube. Same symptoms.
If I jumper the Send and Receive it appears to go away, or at least reduce to a level that is not noticeable to me. However, if I have a couple of pedals in the loop it starts the overdrive/distortion thing. It doesn't matter which pedals, even true bypass pedals seem to do it. I might get away with one pedal, but as soon as I add a second it's really noticeable. Note that this happens even if the pedals are "off" or bypassed.
Different pedal power supplies do the same thing.
The loop has level adjustments for the send and return. I tried just about every conceivable setting there that gave ~unity between the loop engaged and bypassed and the distortion is still there.
So I used another amp and took the Send from that amp into the Receive of the B-52. No problems with pedals in the loop.
So I took the Send from the B-52 into the Receive of the other amp. No problems with pedals in the loop.
I pulled the chassis and don't see any obviously damaged components or cooked traces, or signs of arcing.
I should note that before this I started noticing an occasional "ticking" every once. It would make a tick ~ 6 times and stop. Seemingly at random. Some nights it wouldn't do it at all. It's been doing that for a couple of months, but I can only hear it when I'm not playing and it's pretty quiet and in frequent. I was thinking a preamp tube was just getting tired.
For what it's worth, it's actually a nice smooth overdrive, but I miss having a clean channel and my FX loop at the same time.
Any thoughts would be appreciated. I've attached the schematic for reference.
Thanks!
I have not been able to figure out how to change the title or delete my previous post, so I an admin could delete it I would appreciate it. I've reposted my original post, with a few additions/changes, below:
So I'm trying to figure out why I started getting distortion when the FX loop of my B-52 AT100 is engaged. This started, or at least I first noticed, it at band rehearsal last week when I started playing the intro to Wish You Where Here. I was using the clean channel as usual, but it was not so clean. Not heavily distorted, but more of a smooth overdrive. It's vert touch sensitive. The harder I play, the more the distortion.
After rehearsal I tried to figure out where it was coming from. I narrowed it down to when the FX loop is engaged, which for me is pretty much always.
It's a tube FX loop so I swapped that tube out with a known good tube. Same symptoms.
If I jumper the Send and Receive it appears to go away, or at least reduce to a level that is not noticeable to me. However, if I have a couple of pedals in the loop it starts the overdrive/distortion thing. It doesn't matter which pedals, even true bypass pedals seem to do it. I might get away with one pedal, but as soon as I add a second it's really noticeable. Note that this happens even if the pedals are "off" or bypassed.
Different pedal power supplies do the same thing.
The loop has level adjustments for the send and return. I tried just about every conceivable setting there that gave ~unity between the loop engaged and bypassed and the distortion is still there.
So I used another amp and took the Send from that amp into the Receive of the B-52. No problems with pedals in the loop.
So I took the Send from the B-52 into the Receive of the other amp. No problems with pedals in the loop.
I pulled the chassis and don't see any obviously damaged components or cooked traces, or signs of arcing.
I should note that before this I started noticing an occasional "ticking" every once. It would make a tick ~ 6 times and stop. Seemingly at random. Some nights it wouldn't do it at all. It's been doing that for a couple of months, but I can only hear it when I'm not playing and it's pretty quiet and in frequent. I was thinking a preamp tube was just getting tired.
For what it's worth, it's actually a nice smooth overdrive, but I miss having a clean channel and my FX loop at the same time.
Any thoughts would be appreciated. I've attached the schematic for reference.
Thanks!