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stevel
10-07-2009, 08:29 PM
Why?

What to do?

I have heard that if you plug two amps into the same power strip, they will not create a ground loop (in all cases here, running one guitar into two amps via A/B switch, either, not both).

I've also heard, at various times, if you plug them into the same circuit, and even, if you plug them into different circuits, you can get rid of the ground loop.

TIA,
Steve

Billy Penn
10-07-2009, 08:40 PM
When using multiple amps you need to only ground one of them. Use a ground lift on the others. Unless you use a splitter like the Lehle P-Split or similar that has transformers and ground lifting features. I like that splitter alot. They all can't be grounded or you get a loop.

riffmeister
10-07-2009, 08:42 PM
Lehle, Tonebone, Switchazel, Framptone, are examples of ABY boxes with transformer isolation of the two signal paths and........no GLH.

bigeasy
10-07-2009, 08:42 PM
If it is the AC line going to the amps, yes, usually if they are on the same circuit it's better. But it still doesnít always solve the problem. What should solve the problem is a 3-prong to 2-prong adapter on lower powered amp. This will lift the earth ground connection to the second amp, and use the earth ground for the first one for both.
Give that a try. It may also be something else in your set up I donít know about?

OrangeAD30TC
10-07-2009, 08:44 PM
Try it and address it if you have a problem. Many times you don't need to lift one. You won't always get a ground hum.

stevel
10-07-2009, 08:54 PM
If it is the AC line going to the amps, yes, usually if they are on the same circuit it's better. But it still doesnít always solve the problem. What should solve the problem is a 3-prong to 2-prong adapter on lower powered amp. This will lift the earth ground connection to the second amp, and use the earth ground for the first one for both.
Give that a try. It may also be something else in your set up I donít know about?

So the other thing I've heard is - using one of those 2 prong adapter (or snipping the ground pin off an extension cord) is a good way to get electrocuted.


So it looks I'm reading that, the problem is, you have two amps grounded.

Why does it happen though? What actually causes the loop?

Steve

riffmeister
10-07-2009, 08:58 PM
See my post above and keep both amps grounded and be safe and you will never have GLH. And there are other benefits to using these ABY boxes as well, for example no additivity of cable capacitance when running in Y mode, phase switching if the two amps are not in phase, etc. A good investment that will provide a lifetime of music making joy. :)

Billy Penn
10-07-2009, 09:43 PM
That little gray three to two prong adapter is called a ground lift. If you have multiple amps just ground one. You only need one point of grounding.

smolder
10-07-2009, 09:48 PM
was reading this site today...

http://www.paulrubyamps.com/info.html#Ground

"OK, that optimizes our individual piece of equipment. But, it leaves open the possibility of ground loops when stringing multiple things together. Each thing has it's own mains ground with a reference connection to signal ground. So, the mains power line and the line cords between items form loops. Some amps have a "ground lift" allowing the quick elimination of ground loops by removing the mains ground connection. This SUCKS. Throwing that switch eliminates the safety of mains ground and is NOT needed to solve ground loop problems. The argument is that "if there was a ground loop, then there must be another path to earth, so there's no safety issue lifting the ground." That's crap. Do you trust the cheesy patch cords between your foot pedals to protect you against a B+ short to chassis?? So what's the solution? Think about your mains as extensions of the star ground principle. Keep your equipment physically localized and keep all the mains cords running parallel and tight to each other (there's no surface area to any ground loops and thus no noise pickup). Run them all back to one group of sockets on a wall rather than plugging things in willy nilly around the room. For pub gigs, this is an easy policy to follow. For the big guys, use isolation transformers and run balanced XLR to break the ground loops."

ShavenYak
10-07-2009, 10:07 PM
Smolder's quote is right on. If you use a cheater plug on one amp, and are relying on the signal path to keep its chassis grounded, what happens if the other amp gets accidentally unplugged or the guitar cable gets yanked loose? You have no safety ground, and are now at risk of electrocution.

Listen to riffmeister. Spend the extra money for an A/B switch with isolation transformers.

B_of_H
10-07-2009, 10:29 PM
I always carry a ground lift 'cheater' adapter or 3 in my cable/utility bag for gigs. It really helps sometimes.

Third Stone
10-08-2009, 12:04 AM
this worked for me...and it's cheap.

http://guitars.musiciansfriend.com/product/Ebtech-Hum-X-Hum-Exterminator?sku=150452

jimbo13
10-08-2009, 12:35 AM
Why all the concern about getting shocked? They played without ground plugs back in the 50's like real men. Now shut up and have a smoke you pu$$ies.

bigeasy
10-08-2009, 12:32 PM
The problem with those 2-prong amps then (like the original Fender Tweeds) was that the "ground" switch they had in there actually AC coupled the chassis to one or the other hot sides of the AC comming in. If you had it the wrong way with respect to you, your strings, you would get skocked. Never do this or run one of those amps this way. Cut that cap out out there and add a 3-prong cord. Again, that ground switch was not a ground lift, it actually AC coupled your chasiss to one or the other the HOT AC lines.