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Why does this ABY setup cause feedback?

spentron

Member
Messages
1,795
Yes, yes and also an ABY* is not a mixer in any circumstance, it's a (passive) switchable splitter. If you put a strong buffer before the split, the feedback would stop (in most circumstances) but you'd get approx. nothing from the Rat. (*a normal one without resistors, some might have them even though they reduce performance in the main intended use.)

The cheapest correct way to do this is use something with seperate buffered dual outputs, say a stereo chorus (off), or at least a good buffer and a Y cable to split the signal (this will still scream a moment when you cut off the power). Then remix it with a 100K potentiometer in a box. Place another buffer after this for long cable runs.
 

misa

Silver Supporting Member
Messages
3,667
Agreed with above. If these are simple, passive ABYs, you can clearly see you've created your own feedback loop. Get a Blender pedal if you want to control ratio of clean to distortion in your signal.
 

Laurence

Gold Supporting Member
Messages
9,220
A Super Six Reverb? For real or just illistrative purposes? The two inuts (nonverb/verb) on a reverb Fender are out of polarity with each other because of a diffrenece in gain stages. You would come out of the guitar into an ABY box like the Radial Big-Shot. One out to the amp, one out to the pedal to the amp, and then adjust (dick with) the polarity, transfomer in/out switches until everything is in polarity/phase. You can end up with a clean signal and distorted singal to play with (parallel).
 
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Dave B

Exit... Dual Stage Left
Gold Supporting Member
Messages
1,828
Yes, yes and also an ABY* is not a mixer in any circumstance, it's a (passive) switchable splitter. If you put a strong buffer before the split, the feedback would stop (in most circumstances) but you'd get approx. nothing from the Rat. (*a normal one without resistors, some might have them even though they reduce performance in the main intended use.)

The cheapest correct way to do this is use something with separate buffered dual outputs, say a stereo chorus (off), or at least a good buffer and a Y cable to split the signal (this will still scream a moment when you cut off the power). Then remix it with a 100K potentiometer in a box. Place another buffer after this for long cable runs.
Not that I wouldn't mind trying this if I was handy and knowledgeable with electronics and could take pride in the build, but...

He could go the easy route and get a Boss LS-2 Line Selector, which allows 5 different combinations of its two loops, including running them in parallel, which would solve the OP's dilemma. One of the loops would have the Rat and the other would have nothing (defaults to the straight signal). Since each loop has its own level control, you can blend in the desired amount of original signal with the desired amount of Rat.

Though, if anyone tries this concept with a fuzz or treble booster, since the LS-2 is buffered, you lose the dynamic interplay between your guitar's volume knob and the fuzz or treble booster (yes, I learned that the hard way.)

The LS-2 can turn an amp's series effects loop into a parallel loop, so this is that same principle, just in front of the amp and not in its loop.
 

Balok

Member
Messages
3,609
Might try plugging guitar into a Y splitter, then one side into channel one of fender, other output into Rat, then ch 2 of Fender.
 

stinkfoot

Member
Messages
6,138
Yup - the two ABY's basically create a feedback loop for the RAT. The problem is that the second ABY is being used as a mixer, which doesn't work properly. Only an active mixer can prevent signal from leaking "backwards" like that.

The Boss LS-2 is a great thing to have - it can serve a multitude of purposes, including running things in parallel. Use A+B Mix mode, run the RAT in one of the loops and nothing in the other. Turn the LS-2 off, and the clean signal goes straight through. Turn it on, and you get both the clean and distorted signals in parallel.

The other idea mentioned would be cheap and simple - split as you do now (with the first ABY), but use the amp's inputs to re-join the signals. Hopefully, the input resistors will be enough to stop the signal leaking back to the RAT, if you use inputs 1 and 2 on a silverface Fender (using the normal and vibrato channels would put the two signals out of phase, which would sound weird). In any case, it will not reach back to the RAT's input. It could potentially mess with the output signal a bit, but it won't cause feedback.
 

spentron

Member
Messages
1,795
Not that I wouldn't mind trying this if I was handy and knowledgeable with electronics and could take pride in the build, but...

He could go the easy route and get a Boss LS-2 Line Selector, which allows 5 different combinations of its two loops, including running them in parallel, which would solve the OP's dilemma. One of the loops would have the Rat and the other would have nothing (defaults to the straight signal). Since each loop has its own level control, you can blend in the desired amount of original signal with the desired amount of Rat.

Though, if anyone tries this concept with a fuzz or treble booster, since the LS-2 is buffered, you lose the dynamic interplay between your guitar's volume knob and the fuzz or treble booster (yes, I learned that the hard way.)

The LS-2 can turn an amp's series effects loop into a parallel loop, so this is that same principle, just in front of the amp and not in its loop.
You only lose dynamic interplay that is caused by loading down the guitar signal, the dynamics of normal level control remains. You can't load down the signal and still do a true clean mix, the clean is muddied. Also, the clean part of the mix is affected more by the guitar volume. It's kind of reverse-dynamic because playing louder brings out the clean and letting off brings out the dirt, if the gain is that high.

The setup I described is cheap if you own lots of pedals capable of being buffers and their effects when actually turned on can be useful. I actually got into it because I had a chorus without a mix knob which I can't stand and happened to be using a "stereo' distortion pedal to split the signal.

Back to the OP, that diagram is more accurate if you change most of the signals with one-way arrows to lines with arrowheads at both ends. Signals go both directions when ins and outs are connected together without anything to force the signal to go in one direction (buffers).
 






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