Ground lift concerns

  • Thread starter Thread starter neilli
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neilli

neilli

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First off, I know sweet FA about ground loops, other than how I troubleshot this one!

I'm running an ABY switch and I was getting horrific ground buzzing from my EVH 50W, so I've used a ground-lift adapter on its plug. The other 'side' of the chain is a Marshall 87x powered through a furman pedalboard power conditioner with various pedals before and in the loop. The EVH is powered from a rackmount (i.e. separate) Furman power conditioner, and the signal runs into a tuner, then into the amp (and there will soon be a Hush and quadraverb in the loop) all of which are grounded.

Am I right to think that this means that all signal paths from the guitar are grounded, but the EVH amp chassis is not?
 
Yeah I think you're correct. I need to say that if you ever click over to just the 5153 you'll have an ungrounded amp and that might be dangerous. Also I think that once you add your effects units in the loop you will get that great ground loop back.

Have you tried running the tuner before the ABY switch? Or have you looked into getting an ABY switch with an isolation transformer in it??
 
Yeah, I figured that I'd need to remove the ground-lift if I use the EVH on its own. I've not tried the tuner in front of the switch since I put the ground-lift in: I had it all wired 'properly' when I first got the switch (guitar into wah, then to rack tuner, out to switch) but tore it apart when I got the loop noise. Because the tuner is in the rack with the effect, I'm hoping that adding them into the loop won't restart the problem, but yeah, that did cross my mind too.

I have the Radial Twin Cities which has an isolation transformer but that didn't fix the problem.
 
Did you use a ground lift AC plug? Don't use those. Just break the ground on the 1/4" cable to the second amp
 
neilli":8udhbvia said:
First off, I know sweet FA about ground loops, other than how I troubleshot this one!

I'm running an ABY switch and I was getting horrific ground buzzing from my EVH 50W, so I've used a ground-lift adapter on its plug. The other 'side' of the chain is a Marshall 87x powered through a furman pedalboard power conditioner with various pedals before and in the loop. The EVH is powered from a rackmount (i.e. separate) Furman power conditioner, and the signal runs into a tuner, then into the amp (and there will soon be a Hush and quadraverb in the loop) all of which are grounded.

Am I right to think that this means that all signal paths from the guitar are grounded, but the EVH amp chassis is not?
Click to expand...


never ever lift the ground plug on an amplifier... :no:

Try plugging the amps in the same power conditioner

Read:
http://www.guitarnuts.com/technical/electrical/safety/index.php
http://www.pedalsnake.com/page.php?id=1115#groundLoops
 
PatF":259b5uhv said:
Just break the ground on the 1/4" cable to the second amp
Click to expand...
So just lifting that audio ground on the first cable from switch to amp2 will sort it? Wish I'd tried that earlier!
 
So I tried lifting the ground on the 1/4" going to the EVH and that doesn't work, the loop noise is still there.
 
This might sound like a huge pain in the ass but if I was trying to work out the ground loop issue I'd first set up just the amps/cabs and switcher using standard cables. If you still have a problem then try lifting the ground on the amp end of the cable. Once you've got it quiet in a bare bones sort of config you can start adding elements one at a time and see how it works out.
 
That would be pretty easy - the EVH is pretty close to barebones anyway, and all I'd need to do with the marshall is unplug the effects loop and wah / tuner at the front.

Oblivion DC":r98b7t19 said:
If you still have a problem then try lifting the ground on the amp end of the cable.
Click to expand...

You mean the signal cable right, not power? Does it matter which 'end' of audio with the lifted ground is at the amp - can't see why it would?
 
neilli":7iena36h said:
That would be pretty easy - the EVH is pretty close to barebones anyway, and all I'd need to do with the marshall is unplug the effects loop and wah / tuner at the front.

Oblivion DC":7iena36h said:
If you still have a problem then try lifting the ground on the amp end of the cable.
Click to expand...

You mean the signal cable right, not power? Does it matter which 'end' of audio with the lifted ground is at the amp - can't see why it would?
Click to expand...

Signal cable - correct. I have been told that it matters. I can't verify with personal experience. Try it both ways, one way will reject noise better is my understanding.
 
You'll need an ABY pedal that has an isolation transformer and ground lift switch. A 180 degree switch could be necessary as well to get the signals in-phase. I'd put the amps powered by the same power conditioners the use the ground lift switch on the ABY. If you just lift the ground on a cable you won't have a reference for that signal so you won't get signal or it won't fix the problem.
 
Yup, and that's what I have - Radial Twin City, and it still hums like a mofo unless I lift the actual ground on the EVH, whichever position the groundlift / polarity are in on the pedal.
 
neilli":hsxexlli said:
Yup, and that's what I have - Radial Twin City, and it still hums like a mofo unless I lift the actual ground on the EVH, whichever position the groundlift / polarity are in on the pedal.
Click to expand...

Are you using pedals or effects after the twin city that are for both amps?
 
Something doesn't sound right... Can you post your signal chain from start to finish...

Again, DO NOT lift the ground on either amps AC main!!!
 
GuitarGoat":t3xedd43 said:
Are you using pedals or effects after the twin city that are for both amps?
Click to expand...
Nope, I'd like to, but right now it's straight out of the ABY to each amp chain.
 
rcm78":2zcnduvr said:
Something doesn't sound right... Can you post your signal chain from start to finish...
Click to expand...

'A' output from the Twin City is EVH straight (no tuner, nothing right now).
'B' out goes wah -> tuner -> phase 90 -> Marshall 87x. Loop is TC flashback X4 -> boss CE3 -> TC Petrucci flanger -> CAE line boost -> MXR smart gate.

Neither make noise separately. EVH is powered from a rackmount Furman PM-8 (no ground lift). Marshall and pedals are powered from a Furman SPB-8C pedal board. All pedals are powered through the 9VDC outputs from the board, apart from the X4 which has a power supply. And the Marshall is obviously powered through the 110v output. The twin cities is powered through the 9V DC from the pedalboard too - using a power supply made slightly more background noise.

The rack and the pedalboard are plugged into different outlets, but on the same circuit (old building - all outlets are on the same circuit).

The ground loop noise happens as soon as I plug an audio cable into the EVH - the amp doesn't need to be on.

It doesn't matter which amp is 'A' or 'B' and the ground lift / polarity switches on the ABY don't alleviate the problem.
 
Have you tried getting rid of that pedalboard? Just for testing run any pedals with batteries or with dedicated wall wart style adapters.
 
I've not tried that yet no - I'll give it a go this evening if I have chance (kids LOL).
 
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