my amp is electrocuting me!

[jjhardy]

so this is an odd problem, hopefully i can find a solution. lately, when i play through my rig in my basement my bass strings will give me a tingling sensation, and my amp has a lot of high pitched feedback when no notes are played. i had searched this a bit earlier, and someone mentioned that concrete floors can be a culprit, so i switched the position of my cabs (carpeted one was on top, tolex one was on bottom). this stopped the shock for a while, but it has kicked in again. i tried putting some extra carpeting under the rig, but it did nothing. anybody have an idea whats doing this?

two things that may or may not matter:

it has been very rainy in vermont here lately. thus, i think the basement is more moist than usual.

i have recently started using a vintage randall power amp (early seventies most likely) that has not been kept in pristine condition. ive never had a problem like this with my old head (an ampeg b2r).


any help will be greatly appreciated.

 

[Nick Kay]

I had the same thing in a friend's basement. I think it was a bad ground, which is rather dangerous. My solution?

Wear shoes. The rubber soles insulate you - you're no longer the easiest path to ground.

 

[jjhardy]

ok so i have somewhat determined the problem. my amp is a bit unique in that the power turns on when the toggle switch is up or down, and off when it is centered. when the switch is up, works fine. when it is down, it sounds exactly the same, but shocks me. weird. anyone knows what this means?

 

[bassteban]

To electrocute means to kill w/electricity. Someone call the cops on this guy's amp, then get the zombie squad.

 

[benthughes]

That's Metal.

 

[fdeck]

ok so i have somewhat determined the problem. my amp is a bit unique in that the power turns on when the toggle switch is up or down, and off when it is centered. when the switch is up, works fine. when it is down, it sounds exactly the same, but shocks me. weird. anyone knows what this means?

Stop until this is fixed. It is quite dangerous.

I am not a professional electrician. Still, I can think of some possibilities, and note that there may be more than one thing going on.

* Does the amp have a two-wire cord? That's a no-no these days. It could be a two-wire cord, a three-wire cord with the ground prong broken off, or with a broken ground conductor.

* Some early amps had a power switching arrangement with a three position switch and a capacitor inside that is now referred to as the "suicide cap." If you'd like, I can dig up old Fender amp schematics showing this arrangement. A tech will know how to update this to a proper three-wire cord.

* The outlet in the house may be ungrounded or have a missing ground. The presence of a third prong in the outlet is not an absolute guarantee, if the ground wiring in the house is faulty. An electrician can tell you what's going on in a jiffy.

Mainly I am listing some possibilities to convince you to get help from a decent amp tech, an electrician, or both.

 

[Rick Auricchio]

That amp probably has the line-reverse switch. What it does is the same as flipping the plug around in the outlet.

But those designs were made obsolete when the three-prong plug came into use. I doubt anyone can get a UL approval for such a design nowadays.

That's still a dangerous situation, because usually one side of the AC line is connected to the metal chassis (and your strings) through a capacitor. If the cap shorts, you can die.

 

[Sean S]

Before I knew anything about amps, I used to get small shocks from my dad's old Sceptre (Made in Hamilton, ON; not Sunn). He added a ground plug/path to it and voila, no shocks! One thing I think I remember about that amp was an AC reversal switch. Strange.

 

[Marley's Ghost]

Go wireless.

 

[billfitzmaurice]

the power turns on when the toggle switch is up or down, and off when it is centered.

That dual position switch is how they grounded amps 30+ years ago. It's not safe. Have a qualified technician replace it and replace the 2 wire cord on the amp with a 3 wire cord to ground the chassis.

 

[JohnnyPustular]

+1 to all the earlier posts. This is how things were back in the day-- everyone got shocked, especially bass players.

I can't emphasize enough-- replace your power cord with one that has 3 prongs. Or you can die.

 

[jjhardy]

the cord for the randall is a three prong. however, the outlet it is plugged into has no ground, i've just been using an adapter to make a three prong surge protector plug into it.

 

[jjhardy]

and now i get the feeling that all the guys on the board who know electronics are sitting with their mouths agape...

 

[Rick Auricchio]

Not really agape. But you should never disable the safety ground (the third prong), and to do that you need to use grounded outlets.

This is especially true if you are standing on damp concrete or if there are any nearby metal pipes you can touch. (Do not touch them while using the amp, or you become the path to ground!)

 

[Munjibunga]

The good news is that you can be electrocuted only once. The bad news is that you're dead after it happens. What you are experiencing is an electric shock. Electrocution is defined as death by electric shock. All better now?

 

[Rick Auricchio]

True. I'm shocked that I missed this.

 

[bassteban]

True. I'm shocked that I missed this.

I didn't.

 

[iammr2]

How's your life insurance? Paid up?

 

[McThumpin]

I've got an older guitar amp (roland jc-120) that has the up/down 3 way power toggle, and used to get shocked when it was in the down position. I think it's a reverse ground or something. Solution: always use the up position.

 

[billfitzmaurice]

I've got an older guitar amp (roland jc-120) that has the up/down 3 way power toggle, and used to get shocked when it was in the down position. I think it's a reverse ground or something. Solution: always use the up position.

The position of the switch connects either one leg or the other of the AC supply to the chassis through a capacitor, grounding the chassis. Which position depends on how the AC plug is inserted into the wall socket, and how the socket is wired. It is, in short, a half-assed system that never should have been used to begin with (in Europe and most of the world it never was).