Mini Rectifier loop problem

[waygorked]

I am afflicted with a strange buzz from my MiniRec effects loop. I chased this for a long time assuming it was a problem with my outboard (HD500, several other pedals), but after trying every possible combination of cables, power, and configurations, I ultimately tried taking a 6 foot cable and plugging it straight from send to return. With the loop disengaged, the amp is as silent as would be expected. Hit the loop switch, and it develops both a hiss, a low frequency hum, and a buzz. Moving the cable around leads to changes in the frequency and level of the buzz, and the noise floor goes from tolerable to unacceptable. Same results with different cables.

Any idea what this could be? I love this amp, but the lack of a clean loop makes it a nonstarter. Does this sound like a problem with the loop tube?

 

[Seanthesheep]

Could be a bad ground?

Sounds like either an internal issue or a bad tube buffer?

 

[waygorked]

Do you think there is a point in replacing the loop tube?

 

[Seanthesheep]

No harm in trying.

Maybe demo other mini recs and see if they have the problem

 

[elvis]

If you turn on the loop with NO loop cable and it's OK, then the tube is fine. When you turn off the hard-bypass, the signal goes thru the loop tube whether or not you plug into the loop.

I would look at environment. The fact that the symptom changes as you move the cable suggests you either have a bad cable in the loop, or the cable is imperfectly rejecting environmental noise. Turn off flourescent lights, computers, etc nearby. If you are using a power attenuator or step-down transformer, get them AWAY from the guitar and amp. Move ANY equipment with a transformer away from the amp. Move any wall-warts (inline transformers) away. These all broadcast lots of noise.

 

[11justin22]

Mine has issues with my pedal board in certain venues. Don't know why it does it on some and not the others but I took a ground lift and plugged into my pedal board power supply and it solved my problem

 

[elvis]

Almost all venues have cut costs in their power grids, so they are almost always a disaster. They are also always DIFFERENT. So you will get varied problems.

My rules:

1. NO ground lifts. It's dangerous enough with the grounds connected.
2. ALL gear into the same outlet. Two different AC circuits = ground loop.
3. Isolation transformers between AC-powered gear. That solves a lot of problems.
4. Balanced cables wherever possible.
5. Rack power conditioner.