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Why Running Two Amps Gives You a Buzz (And How Buzzkill Fixes It)
You've got two amps set up. Maybe you're running wet/dry, maybe just stereo. Everything's dialed in, sounds huge, and then that hum shows up. Not from a bad cable, not from a bad pedal. A ground loop.
The second you send your board to a second amp, you've created two paths to ground. And those two paths can fight each other. That fight is what you're hearing as buzz.
Here's the part that makes ground loops so annoying to diagnose: they're often venue dependent. You can build your rig at home, run it exactly the way you plan to at the gig, and it's dead silent. Then you load in the same board, same two amps, same guitar, to a different room, and suddenly you've got a ground loop. There's no way to predict it walking into a new venue. That unpredictability is exactly why Buzzkill exists.
How it actually fixes the problem
Inside Buzzkill is an audio transformer. It breaks the ground connection on one of your amps while letting audio pass as normal, so the two amps stop fighting each other over ground and the loop disappears.
As a side note… don't mess with your mains power cable to try to kill a ground loop. That's an electrocution risk, and it's not worth it. Buzzkill does the same job the safe way, by isolating your audio ground instead of your power ground.
Patching it in
Say your last pedal before the split is a stereo reverb. Left output goes straight into amp one's input like normal. Right output goes into Buzzkill, and from Buzzkill into amp two's input. That's it. No power needed, it's fully passive.
Because it's passive and this simple to patch in, you can just keep one in your gig bag and only use it when a venue actually gives you a ground loop. No loop, no need to patch it in.
How many do you actually need
Rule of thumb: one less Buzzkill than the number of amps you're running. Two amps, one Buzzkill. Three amps in a wet/dry/wet setup, two Buzzkills. Four amps, three. Ten amps, nine. One amp always stays as your reference path to ground, everything else gets isolated off of it.
The red button
That button isn't just there to fidget with. It flips the polarity on Buzzkill's output. Here's why that matters: put something like a Vox AC30 and a Fender Twin together in a two amp rig and there's a decent chance they'll end up out of phase with each other. In practice that sounds thin and honky, because while one speaker cone is pushing out, the other is pulling in, and they're cancelling frequencies against each other instead of working together. Hit the button, and now both speakers move in the same direction at the same time.
A couple other things it's handy for: You can convert unbalanced signal to balanced (TS cable to Buzzkills input) and use a TRS Cable on Buzzkills output - and vice versa.
If you're running parallel and one pedal in that chain happens to invert polarity on you, Buzzkill can flip it back in line with the rest.
If you're running parallel and one pedal in that chain happens to invert polarity on you, Buzzkill can flip it back in line with the rest.
The takeaway
Single amp in series, you don't need this. Two or more amps, Buzzkill is cheap insurance for the gig you didn't know was going to give you trouble.
If you're not sure which camp you're in, email us at info@goodwoodaudio.com before you buy one. I'd rather help you troubleshoot for free than sell you something you don't need.
