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Guitar amp ground lift myth?
Guitar amp ground lift myth?
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Old 20th September 2019, 03:36 AM   #1
6V6dude is offline 6V6dude  Australia
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Default Guitar amp ground lift myth?

I have a stand alone tube guitar preamp connected to guitar amp which is in another room. This creates ground loop and hum. How about ground lift on the preamp to eliminate the hum by just using the lead for ground. By chance I came across article on some website claiming one can get electrocuted this way which I believe is impossible. What are your thoughts on this? Excerpt from the article: "Do not do this. If you're using a ground-lift adapter on one amp that is connected to the other grounded amp through cable, when you touch both guitar plugs at the same time, you will get a jolt of electricity through your body."

Last edited by 6V6dude; 26th September 2019 at 01:37 AM.
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Old 20th September 2019, 04:22 AM   #2
6L6 is online now 6L6  United States
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Guitar amp ground lift myth?
You've got the answer already - the devices are grounded through the instrument lead.

So if there's a fault, those currents will be attempting to find ground through the whole circuit, including the guitar itself. Painful. Also, there is a chance, depending on the various devices being used that the whole circuit becomes elevated since it has no ground reference, and if you touch anything on ground, it's going to cause a zap.

The worst case is if you use a cheater and have the live and neutral reversed - that will usually make for a painful experience when you touch anything else.

So is your question a myth? Absolutely not -- you've just been lucky so far.
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Old 20th September 2019, 04:33 AM   #3
stratus46 is offline stratus46  United States
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Quote:
Originally Posted by 6V6dude View Post
I have a stand alone tube guitar preamp connected to guitar amp which is in another room. <snip>
I don't think anyone here will sanction using a ground lifter as a permanent solution. For testing OK. The protective ground is to be certain no lethal Voltages (and currents) are on the ground. I don't know if it's still done but it was common on tube gear with a two wire cord (non polarized plug) to use use a 1nF cap from one terminal to the chassis. The instructions were to reverse the plug to reduce hum. That connection to the power line is a big part of the problem and while it didn't kill me, it DID get my attention. Look into isolation transformers for either the power line and / or the signal cable. That will break the ground loop without being a safety hazard.

G
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Old 20th September 2019, 05:28 AM   #4
Mark Whitney is offline Mark Whitney  Netherlands
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This is what can happen.YouTube
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Old 20th September 2019, 06:56 AM   #5
Tesla88 is offline Tesla88  Italy
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I would ground preamp and amp as they should and put a passive line / line transformer or a DI between preamp output and amp input
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Old 20th September 2019, 07:07 AM   #6
Bill Coltrane is offline Bill Coltrane  Netherlands
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I've been electrocuted on stage several times, although not as dramatic as in the posted video.

Use aes48 or an isolation trafo.
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Old 20th September 2019, 08:33 AM   #7
thoglette is offline thoglette  Australia
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I'm with Bill and Tesla. If you've got hum problems, use an isolation transformer in the line level lead between the pre-amp and amp. Preferably a pair (one at either end with a balanced, 600ohm line between). Jaycar and Altronics both sell these (10k:10k and 10K:600CT) for not much money.

If that doesn't fix your problem you need an electrician. One with a brain. As your building wiring is broken (probably in a weird way) or your amp/preamp is faulty.
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Old 20th September 2019, 08:38 AM   #8
JMFahey is offline JMFahey  Argentina
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That one was fake, by own admission.

Try this one for real

YouTube

the electrocuted Guitar player suffered MASSIVE heart damage, now a good part of it is non functional scar tissue, cant play any strenuous sport, his life is ruined.

hes alive only because his Father in Law who was on the first row had recently finished a CPR course and assisted him immediately, plus by sheer chance there was an ambulance (and paramedics) in the premises so they were by him within 4 or 5 minutes.
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Old 20th September 2019, 10:05 AM   #9
TBTL is offline TBTL  Germany
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Ouch, his left hand was on the metal guitar strings, his right hand on the metal microphone. That would lead the current to flow through his heart.
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Old 20th September 2019, 04:30 PM   #10
Max Headroom is offline Max Headroom  Australia
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Been there done that, next times are not such a surprise.


Dan.
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