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  #1  
Old 05-08-2001, 09:27 PM
sixstringshredda sixstringshredda is offline
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ok this is really weird. I'm playing at practice right.. and i switch over to this clean sound on my amp, and all of a sudden it starts crackling at certain points of my song (most of the time when i play the open B string). thinking at first maybe i was too loud or i had too much highs or mids, i adjusted my settings and tried again..

i ignored it and went on with the rest of the song, but when i sang into the microphone, i got a big ZAP and it hurt like all hell.

Now i figure its gotta be an electrical prob.. so i flip the amps ground switch, both ways and then nuetral again.. no effect..

i unplug my amp from the power surge, and plug it back into a different slot in the strip and its fine.

but only temporarily. minutes later it starting crackling and i got electricuted once again. whats wrong and how do i fix it?
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Old 05-09-2001, 01:00 AM
Bardsley Bardsley is offline
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This sounds pretty serious, I would send it away for repairs immediately. Don't try to fix this yourself as you could damage yourself or your amp. I advise that you get this seen to quickly, and until then don't use your amp.
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Old 05-09-2001, 01:34 AM
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Lordathestrings Lordathestrings is offline
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I suspect the ground connection of your amp. You get 'lifted' when you touch the mic because the shell of the mic is grounded (and you definitely are not).

This can be lethal!!!

I'm going to assume you're more artistic than technical. Also other folks reading this may not know anything about this stuff, so please, bear with me.

Most guitars come from the factory with the bridge or tailpiece tied to the shell of the output jack. This provides a ground connection from the strings, via the the jack cord, to the amplifier chassis. In most situations, this is a nice, safe, quiet setup.

The GND switch (usually installed next to the amplifier power cord), connects a small capacitor from Ground to one of the AC power lines. Usually (not always), the amp will be quieter when this capacitor is connected to the Hot line. Sometimes, connecting to the Neutral works better. But then again, somtimes it doesn't work at all...

First, inspect the power cord, and the plug.

If the cord has been stepped on too often, or pinched under some heavy equipment, it may be shorting the Ground line to one of the power lines. Another common problem is the fitting where the cord enters the chassis. If the cord has been bent sharply at this point, it may be shorting internally.

Examine the plug closely. Molded-on plugs, in particular, can be damaged internally if they have been pulled out by the cord. It may look cool to yank on the cord five feet away from the socket, but how cool is it to electrocute yourself? If the plug is the type that can be taken apart, inspect the connections. A small stray strand of wire can cause big trouble.

If the plug and the power cord are OK, its time to see your favourite tech. Things get a little trickier, and a lot more dangerous from here. I'm going to explain some more of the trouble-shooting process so you can have an intelligent discussion with your tech. Don't try this at home, folks!

The Ground switch is the next thing to be checked. My guess is that the switch is broken internally, and is not actually disconnecting the capaciter when you move it to the 'neutral' setting. (Not to be confused with the Neutral line of the AC power).

Then the capacitor. I call this a 'small' capacitor because it has a numerically small value of capacitance. In this case, the low value is important because a small capacitance will conduct high frequencies better than low ones. The 50/60 Hz AC power frequency is considered to be low, compared to the transient spikes that can make clicks and pops.

A partial failure, known as a 'leaky' capacitor, allows too much current to flow. In your case, this would mean that the 'ground' of your amp, and your guitar, (and you!) would actually be 'hot' relative to a 'good' ground (like the mic and it's stand).

There are other points in the circuit that can cause this problem (like cracked insulation in the power transformer or any of the high-voltage wiring), but the capacitor and your Ground switch are the first items to check.

*** Please take your amp to a qualified tech. This stuff can kill you. ***

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Old 05-09-2001, 04:35 PM
sixstringshredda sixstringshredda is offline
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hey guys thanks. figured out the exact problem today;i was running my amp cord into a surge protector that DIDNT have the ground plug, which was going into an extension cord that DIDNT have the ground plug.

I got new extension cords and surge protectors and the problem was fixed.

Thanks a lot.
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Old 05-09-2001, 11:07 PM
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Lordathestrings Lordathestrings is offline
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Happy Happy Joy Joy

I'm gald to hear it was the simplest, cheapest fix that did it for you. I'm not sure you're completely out of the woods yet, though.

The Ground line is there to provide a path to drain away potentially dangerous voltages that appear on the frame or the chassis. My point here is that the voltage that was on your amp's chassis, (and anything connected to it, like your guitar and your hands), is now being drained by the now-continuous Ground wire. There should not be any voltage there for the Ground wire to protect you from! Your amp still needs to be checked out by a competent tech.

I'm also shocked, (shocked I tell you!!), to hear that you were using ungrounded power cables!

[Edited by Lordathestrings on 05-10-2001 at 12:26 AM]
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Old 05-11-2001, 07:22 PM
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Sometimes you have to. A friend of mine's old practice room had no grounds (nor any room in the upstairs of his old house). I've also been shoked by another friend of mine touching his guitar (and strings) to my strings... talk about an unhappy bassist. Of course, his amp has been known to shock anything that happens to sit on it. Of course, his amp doesn't have a ground wire anyway.
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Old 05-12-2001, 04:59 AM
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Lordathestrings Lordathestrings is offline
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Isolation Transformers!!!

Please, people, take care out there! Getting shocks from your equipment is not part of 'paying your dues'.

An isolation transformer prevents your rig from having any direct connection to either the Line or Neutral of the AC supply to any other part of your stage setup. Without a complete circuit path, there can be no flow of current. This won't protect you against a really determined idiot, but it greatly reduces the number of opportunities to fry yourself.

As I said earlier, The safety Ground wire is there to drain away any voltage that appears on the chassis of the amp. The point is, there should not be any voltage there, in the first place! If you're getting shocks from any part of your setup, there is a problem that needs to be cleared up NOW!

[Edited by Lordathestrings on 05-12-2001 at 06:06 AM]
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