Best way to deal with two amp (stereo) ground loop buzz?

[ER]

The experts out on the web don't seem to be trusted on this. So far what I've seen looks dangerous, or ineffective. Is there something I can do inside of the amps themselves to get them to play well together? What's a better fix, at the plug, or isolate one or more of the signals with isolation transformers?

Signal chain is Guitar> wah> fuzz> L(mono) TC Gmajor2>> stereo volume pedal>> D-style twin and Fender Twin.
=BZZZZZZZZZ, unplug either amp input and it's silent.

[xtian]

ABY switch with iso transformers. I got this one and like it: Radial Bigshot ABY.

[R.G.]

Web experts suffer from the Dunning-Kruger effect a lot.

What is happening is that one, or more likely both amps have some noticeable AC power line leakage. This problem is worst in two-wire amps and still exists in properly wired three-wire amps to some much smaller degree.

For illustration, imagine that one of the amps has nearly zero leakage of AC power, and the other is much worse. In both amps, signal ground is connected to the amplifier's chassis. In the amp with nearly zero leakage, the signal ground sits at ... zero volts. In the amps with some leakage, the AC mains leakage drags the signal ground up and down by some millivolts.

The leaky amp sounds quiet with only it being used because the guitar ground is being dragged up and down that same few millivolts, and so the amp only amplifies the guitar - no hum results. But when you connect the signal grounds of the two amps through the cable shields, the amp with leakage drags BOTH grounds up some and down some, and so both amps hum.

Of course, in reality both amps leak some. You hear hum from the difference between the two. Same principle.

The quick and easy solution is to use transformer isolation. I've done several variations of how to do that for cheap if you can build electronics., Here are a couple. You only need isolation, not the ABY stuff for what you're doing, but most people somehow think this is tied together. It's not.
www.geofex.com/fxprojex.htm
http://www.geofex.com/FX_images/TransformerSplitter.pdf
Don't do ground lifts. The amp - and life - you save could be your own.
Ask questions where this is not clear.

[Roe]

ABY switch with iso transformers. I got this one and like it: Radial Bigshot ABY.

yes, I prefer the lehle stuff though.

[norburybrook]

ABY switch with iso transformers. I got this one and like it: Radial Bigshot ABY.

yes, I prefer the lehle stuff though.

I've got the Radial ABY (first version) and it does change the tone I've found. For running two amps simultaneously I have the Lehle P split and that seems to sound better to me, doesn't load the guitar/amp in any unusual way.



MC

[Reeltarded]

Lehle! I have the red things you can network for multiple splits and program to ABC or ABY.

They only have ONE MAJOR FLAW

The switch buttons have exactly as much clearance as the diameter of a guitar cable.

[ER]

Thanks guys, it sounds like isolating the signal is the way to go. I think I'll try a set of those xicon isolation trannies after the stereo volume pedal and make it part of the pedal board, or maybe just put them in the pedal itself and lift the output jacks with plastic sleeves and washers.

It's one of those ernie balls that acts as a regular volume pedal, or you can kick the toe switch and it pans between A and B, so having isolators built in could be a cool trick since it's basically a variable A/B/Y. I put it on the outs of the TC so I can mute it for tuning. Does anybody know how HAD modded Larry Carlton's volume pedal? Not sure if it's an active buffer or a passive treble bleed like you would put on a guitar pot, that might be good to throw in there at the same time.

[R.G.]

Be aware that just using a pair of those Xicon transformers without driving circuitry will likely produce bass loss. The Xicons are voice grade, only guaranteed down to 300hz - it's one reason they're so cheap. You'll get pretty severe attenuation in the lowest octave, some in the second octave from bottom in standard tuning.

On the high end, the lowish impedance of the transformer and loading may also cause treble loss, or possibly even some treble peaking if the transformer leakage and loading align the stars just a bit wrong.

That's the reason I went for an active drive for the cheap Xicons. It cures both the treble and bass loss. But it does require power to the active drivers.

There are transformers that might do the job without active drivers. But these tend to be expensive - $20 -$50 per transformer the last time I touched that issue.

[ER]

Thanks RG,
The TC will do up to +20dB on the outputs, but maybe I should look at something else in case I ever do any octave down or drop tuning stuff.

[R.G.]

The TC will do up to +20dB on the outputs, but maybe I should look at something else in case I ever do any octave down or drop tuning stuff.

I think I'm completely misunderstanding you. Be gentle and correct me, OK.

+20db is a measure of signal amplitude (loudness, in volts).
Octave down or drop tuning is a frequency response thing.

The lowest frequency of a guitar in standard tuning is about 82Hz. One octave up to the middle E is 164Hz, and another octave up to the high E string is 328Hz. A low frequency rolloff at 300 starts reducing response with your high E string and everything lower. It's not just octave down or drop tuning.

Again, I may be misunderstanding you.

[ER]

I'm using a TC Gmajor2 rack effect unit for the stereo split, the analog output stage can be set for a professional line level at + 2, 8, 14, or 20dBu or consumer line level at -10dBV and both the input and output level can be adjusted on the from panel from 0 to max with their own knobs, which should be plenty to drive a transformer without loss, or do you have a filter to bring up the low end along with the driver to use those transformers in your circuit? The point in the signal I want to isolate (lift the ground loop) is not at instrument or mic level like a typical a/b/y box would be used. I'm using the consumer line level setting since I'm going into the inputs of the amplifiers and not using the effects loops. The outputs can be either balanced with a TRS cable, or unbalanced with a typical guitar cable.

The effect unit has a lot of pitch shifting capabilities, I typically use an octave up harmonizer like an octavia, but will probably use an octave down effect also on occasion (41.2Hz), and I do play in drop D sometimes, or a half step down and dropped (Db/C#@69.3Hz) so a 300Hz roll off wouldn't work for what I want to do.

[saintgillis]

Another solution for splitting and ground isolating : http://sub-continental.com/dd/splitterbox3isolated.html

[blackeye]

ABY switch with iso transformers. I got this one and like it: Radial Bigshot ABY.

I just picked up the Radial Twin City which is, as I understand it, a buffered version of the Bigshot--so no tone degradation on that isolation transformer side. So far I'm really liking it. A little more expensive, but a simple solution.