My amp shocked me
- Thread starter Toki987
- Start date
apl
Stand Up Comity
I may be totally wrong, but I think some old amps have switches that allow you to ground to either side of the outlet, so ground could be hot or neutral, but makes no sense. I think that's how guitarists can shock each other, though.
This can't be right, though, because your strings are grounded through the amp, and I don't know why you wouldn't get shocked playing.
Although your playing may shock people, but that's different.
This can't be right, though, because your strings are grounded through the amp, and I don't know why you wouldn't get shocked playing.
Although your playing may shock people, but that's different.
Toki987 said:
First, check the AC circuits that your gear is plugged into. Radio Shack sells a cheap circuit tester that can save your life; it's a yellow plastic block with a plug on one end and three LED's on the other. The pattern of LED's that light up when you plug it in tell you whether the circuit is OK, or has hot-neutral reversed (which will run things that plug into it but can kill you), or any other way the wiring can be screwed up.
You bass head is not ground lifted, is it? That's a dangerous practice, but if you must do it, first connect all the signal wiring with the amp unplugged from power.
apl said:
The operating phrase here is "through a capacitor"; a 0.05 microfarad cap is pretty much an open circuit to 60 Hz. The effect of the difference in that switch position is minor - it means that you either get a mild shock or none at all when you touch the amp chassis and an earth grounded piece of metal at the same time. If you get a major shock, something else is wrong.
In any case, the OP said that he was plugging into the "recording out" of the Fender head, which implies to me that it is a newer design. Check me on this, but I believe that that grounding switch went away with the advent of three conductor (hot, neutral, ground) power.
The ground switch stayed with three-prong outlets. Amp users do one thing not a lot of other people do: they kiss mics while being attached to two 120 volt supplies, essentially connecting them. This can provide a return path for current.
The ground switch reverses the polarity of the AC. The polarity of the AC in the amp and PA must be the same, or you will get shocked. The amp AC is swinging positive while the PA AC is swinging negative if the AC is reversed in the amp. Your lips provide a connection for current to flow between these opposite voltage potentials.
The ground switch stayed to protect people from shitty wiring.
I carry a meter, and check for voltage between the mic windscreen and guitar strings. There shouldn't be any.
The ground switch reverses the polarity of the AC. The polarity of the AC in the amp and PA must be the same, or you will get shocked. The amp AC is swinging positive while the PA AC is swinging negative if the AC is reversed in the amp. Your lips provide a connection for current to flow between these opposite voltage potentials.
The ground switch stayed to protect people from shitty wiring.
I carry a meter, and check for voltage between the mic windscreen and guitar strings. There shouldn't be any.
foreverain4
New member
i have a sunn 200s that was doing the same thing. it only has a 2 prong plug. i removed the bottom of the plug so that i know which side is positive. white wire goes into the large slit, black goes into the small. havent had any problems since...keep in mind, this is not a ground problem, this is actually voltage! people have been killed in such situations. be safe man!!
easychair said:
There is no way for an amp to change the "polarity" (by this I assume you mean phase) of the AC being supplied to it. I refer you to the schematic of a Fender Bandmaster at http://www.ampwares.com/ffg/schem/bandmaster_5e7_schem.gif
The ground switch is in the center near the bottom, and it connects a .05 microfarad capacitor between the chassis and either the hot or neutral leg of the AC supply. I confess that I don't fully comprehend what this is supposed to do , but it doesn't change how the AC is wired to the amplifer circuit. It just selects to which node the chassis is capacitively coupled, though I don't know why you'd ever want the chassis coupled to hot.
My assumption has always been that this switch was designed into amps before plugs were polarized, i.e., before one prong was bigger than the other, so that the user could always link the chassis to the neutral leg regardless of which way the plug was inserted. But, as I say, that's an assumption.
Anecdotal data: I have two old Fender amps which both (originally) had two prong unpolarized plugs. They both have the switch. I also have several much newer amps, and they all have three prong AC cords and no switch. YMMV.
FALKEN
*************************
oh man.
I was playing at a club about 3 months ago and every time my lips touched the mic I got a small shock....
of course I didn't know this until we had already started our set, so I just finished it out...
I suspected a bad mic cable at the time.
Never once happened at practice though.
I was playing at a club about 3 months ago and every time my lips touched the mic I got a small shock....
of course I didn't know this until we had already started our set, so I just finished it out...
I suspected a bad mic cable at the time.
Never once happened at practice though.
punkin
Univalve & Avatar Speaks
I see reference to ground through out the circuit diagram but from the power receptacle side I don't see the connection. The chassis ground should have a connection to earth unless by some weird design, they want it to float...that would simply be nuts since everything else you might make contact with will be earth ground.
That switch is kinda strang but with that capacitor on there, all it's doing is selecting which leg of utility to add a little decoupling/filtering to. Perhaps an attempt to remove a little excess hum or noise. It's not switching polarity.
That switch is kinda strang but with that capacitor on there, all it's doing is selecting which leg of utility to add a little decoupling/filtering to. Perhaps an attempt to remove a little excess hum or noise. It's not switching polarity.
punkin
Univalve & Avatar Speaks
I just had another quick look at those schematics...the output and input jacks are tied to what is described as ground. The power supply section doesn't indicate exactly what ground is but if the drawing is correct, ground is not derived from that power plug. Take that just a bit further, if you plug anything into the input jack that is grounded (to include yourself when touching the plug end of the guitar cable) tag, you're it!
Toki987
Rock Steady
The amp head is a '77 Bassman 135. It has a 3 prong for house ground, and a ground reverse switch. I was pluggin a cord in the recording out, that was already plugged into a channel strip for the PA. I touched the chassis with one hand while holding the cord in the other. I thought I was about to have a heart attack.
punkin
Univalve & Avatar Speaks
I don't see the "record out" plug in the schematics. It sure seems like something isn't grounded or it used to be and isn't anymore. I'd get the $10 radio shack volt/ohm meter out and start measuring the simple stuff...like maybe the power cable is gone bad or the chassis ground came disconnected inside.
Are both devices plugged into the same utility circuit? If so, verify that ground is on the third wire of the outlet. As someone else also suggested, make sure the utility jacks are wired correctly and that they're all wired the same!
Since you say that you were connecting two piece of gear together is a big clue. Get both device close together but not touching, plug them in...and don't touch them at the same time...put a volt meter between them (ground and ground). The difference between them should be zero volts. Since you got shocked they probobly won't be.
Follow this up by measuring chassis ground of both devices to one of the unused the outlet grounds...this also should be zero ohms, zero volts. The device that reads high with reference to utilty ground is floating which is the likely device cuasing the difference in potential and your synaptus interruptus.
Are both devices plugged into the same utility circuit? If so, verify that ground is on the third wire of the outlet. As someone else also suggested, make sure the utility jacks are wired correctly and that they're all wired the same!
Since you say that you were connecting two piece of gear together is a big clue. Get both device close together but not touching, plug them in...and don't touch them at the same time...put a volt meter between them (ground and ground). The difference between them should be zero volts. Since you got shocked they probobly won't be.
Follow this up by measuring chassis ground of both devices to one of the unused the outlet grounds...this also should be zero ohms, zero volts. The device that reads high with reference to utilty ground is floating which is the likely device cuasing the difference in potential and your synaptus interruptus.
Light
New member
FALKEN said:
I once worked for a guy who WANTED me to put about 12 volts between his mic and his guitar. He liked it. Something about making him feel a little more Rock and Roll or something. If it happened (and sometimes it does) he got it, but if it couldn't be done safely, then no go.
Obviously, he rarely got it.
Light
"Cowards can never be moral."
M.K. Gandhi
Last edited:
punkin said:
No, it's not. But if the hot is connected to the amp chassis by the switch being in the wrong position or the outlet being wired wrong, and you touch the ground of another piece of gear, you make a connection between hot and neutral. You get shocked.
There is nothing necessarily wrong with the amp. The above could happen in a perfectly working amp, and a correctly wired outlet, if the switch is in the wrong position.
Those switches are bad news, Toki. I'd have a tech remove it and wire the thing right. There is really not much need for the safety ground to be hooked to either leg with a three wire plug. It's easy in that amp, you should just be able to unhook it, basically.
They are handy if an outlet is wired wrong, but like I said, you can get shocked even if everything is OK, so at least be careful. Punkin has a good idea about checking. I check every time with mics and tube amps.
Last edited: