Tweet
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.
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 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 significantly noticeable. 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 these 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.
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!
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 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 significantly noticeable. 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 these 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.
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!