Members tocs100 Posted June 20, 2008 Members Share Posted June 20, 2008 My guitarist has two Behringer V-Tone amps that he's switching between clean and dirty. He's tried two A/B boxes though (Whirlwind & Boss), and they both are feeding back (not just squeal, but roar too ) on the dirty amp. I'm thinking these A/B boxes are missing buffers (and probably tie-down resistors too), so the output is bleeding back into the input, creating a loop. I suggested he try Boss' LS-2 Line Selector. Any ideas/advice? Link to comment Share on other sites More sharing options...
Members OnWingsOfLead Posted June 20, 2008 Members Share Posted June 20, 2008 I built a very simple A/B box in about 10 min for my board. It was super simple, and it introduces 0 noise. Search schematics for the Eric Johnson A/B box Link to comment Share on other sites More sharing options...
Members tocs100 Posted June 21, 2008 Author Members Share Posted June 21, 2008 Bump for more advice. Link to comment Share on other sites More sharing options...
Members andreas Posted June 21, 2008 Members Share Posted June 21, 2008 If the dirty amp is squealing when the clean amp is activated, chances are the A/B box doesn't shunt the unused output to ground. That leaves the input to the dirty amp hanging, much the same way as when you accidentally unplug the cable at the guitar end. Try plugging straight into the dirty amp, and turn down the guitar volume (shorting the input to ground). If the amp still squeals, the problem is in the amp (possibly a microphonic preamp tube). If not, turn the guitar volume up. If it starts squealing now, the pickups may be microphonic. If it still doesn't squeal, the problem is definitely in the A/B box. /Andreas Link to comment Share on other sites More sharing options...
Members OldCrankyDouche Posted June 21, 2008 Members Share Posted June 21, 2008 Sounds like a tube issue that I had to deal with when I had my Classic 30. JC-120 FTW. Link to comment Share on other sites More sharing options...
Members strat-man Posted June 21, 2008 Members Share Posted June 21, 2008 Tell him to buy a EH Nano Switchblade and rewire the 3PDT switch using the X pattern ground lift wiring shown in this link; http://www.fulltone.com/qaframe.html I,ve done this and had NO problems with signal crossover when running 2 amps, even at high gain. Link to comment Share on other sites More sharing options...
Members tocs100 Posted June 21, 2008 Author Members Share Posted June 21, 2008 If the dirty amp is squealing when the clean amp is activated, chances are the A/B box doesn't shunt the unused output to ground. That leaves the input to the dirty amp hanging, much the same way as when you accidentally unplug the cable at the guitar end. Try plugging straight into the dirty amp.... Straight into the solid-state, dirty amp is fine. I think you hit it with the grounding problem. Thanks everyone. Link to comment Share on other sites More sharing options...
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