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Old 06-07-2014, 08:19 PM   #1
gocosfs
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valve amps and ground lifts ?

i have read were groundlifts can be dangerous with valve
amps .

what does someone do if there in a place that is old enough
were grounding was not code for the building. how
do you ground an amp to avoid potential dangers ?

also is it just as dangerous for SS amps as it is with valve amps
to groundlift ?
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Old 06-07-2014, 10:01 PM   #2
Invader Jim
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SS amps use far lower voltages than tube amps (high-power SS amps can use 70-100v depending on output power and low-power SS practice amps typically use 20-40v). Low-power tube practice amps usually use 200-300v or so and high-power tube amps can use upwards of 600v. While lower voltages are generally less dangerous, it is still possible to be killed, especially if you have a heart condition that you are unaware of. It all depends on a myriad of factors, including the available current, the temperature, humidity, and the amount of Gatorade you drank that day. Lifting your gear's ground connection is usually not a good idea. If you absolutely had to, or were in a situation where there is no ground connection at the wall receptacle, you can greatly increase the safety of the rig by using an isolation transformer. This will isolate the neutral wire of the mains from ground (the neutral and ground wires are connected together inside the breaker panel or at the kW/hr meter outside the house).

Having said all that, the amp's power supply should be isolated from the mains input side by the power transformer, unless something is catastrophically wrong. Plugging into a killer tube amp is very rare, but it has happened. The whole reason that an amp chassis is grounded is to prevent the chassis from becoming live with any appreciable voltage or static charge.

As for grounding an amp in an old out-of-code house, you can drive an 8ft iron rod into the ground and use that, or you could probably get away with connecting the amp to a copper cold-water pipe... Or you could use an isolation transformer. It wouldn't ground the amp, but it would make it impossible for you to get shocked unless you grab both the hot and neutral mains wires"at the same time". The reason you get shocked in the first place is because your body is a path to ground. An isolation transformer takes the ground out of the equation for anything plugged into it.

This info is based on US wiring. Things in the UK may differ slightly or completely. If I am wrong about any of this, someone please correct me. It's been a while since college...
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Old 06-07-2014, 10:29 PM   #3
gocosfs
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that is such a great explanation i really appreciate it .



Quote:
Originally Posted by Invader Jim
The reason you get shocked in the first place is because your body is a path to ground..



^^^ isnt this the reason guitars are noisey amped until you grab the fretboard
the whole circuit (you the player ) completes the path to ground ?
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Old 06-07-2014, 11:25 PM   #4
Invader Jim
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A pickup os just a coil of wire, electrically, and makes an exellent directional antenna for all the junk in the airwaves. When you touch the strings or other grounded metal, it quiets or eliminates the hum because your body is a path to ground.

Honestly, now that I think about it, I'm not quite sure how it works (I'm not ashamed to admit that I've forgotten more than I'll ever know ) but that's how it is. I need to study up on it to refresh my memory...
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Old 06-08-2014, 12:46 AM   #5
jthm_guitarist
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All right, except in technically the strings are grounding you and not the other way around. You might be a path to ground enough to be affected by high voltage, but not enough to be a shield for noise (unless you're soaking wet and sitting naked on the radiator or something).
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