masiye
1 post
Sep 21, 2011
8:56 PM
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I could use some help. Recently bought a '55 Fender Champ Amp. Playing a vintage Jt-30, sounds like a dream. If I touch a mic going through the p/a I get shocked while holding the harp mic attached to the amp. I had the power cord changed to a 3 prong but the problem persists.
How do I successfully lead the band as a lead singer while still holding and playing my vintage mic/amp set up? I've seen plenty of you guys do it online.
Thanks!
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5F6H
846 posts
Sep 22, 2011
3:21 AM
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You're getting shocked by the amp not the PA, the PA is just offering a path to ground (as would a water pipe or any other physically conductive medium connected to ground that you may come in contact with). Fit a 3 prong, grounded AC cord then the amp is safe without any other devices needing to be carried about/remembered. If you are not up to fitting the cord yourself a tech will be able to fit one for the price of the cord & a minimum bench fee.
www.myspace.com/markburness
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MrVerylongusername
1955 posts
Sep 22, 2011
3:33 AM
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He's already done that.
*edit* - Ah I see... I presumed he was talking about the amp when he said he'd changed the cord
Last Edited by on Sep 22, 2011 3:35 AM
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Ray
353 posts
Sep 22, 2011
4:52 AM
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Would the 'death cap" have anything to do with this problem?
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Pluto
173 posts
Sep 22, 2011
5:41 AM
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MR, very cool. I didn't know such a device existed, and its not expensive.
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kudzurunner
2700 posts
Sep 22, 2011
5:42 AM
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I should note that "massive" emailed me privately with his question and I encouraged him to register for the forum and put his question to the general company, assuring him that he'd get good feedback.
@massive: please clarify: at this point, do BOTH the PA head AND your amp have 3-prong grounded plugs?
Something I've run into once or twice is amps with grounded plugs that nevertheless create a buzz or hum when you're using them both. Apparently they were wired in reverse--in reverse from each. Each was grounded, in other words, but the left and right terminal of each plug went to "opposite" (in polarity terms) wires.
The solution was to retrofit one of the grounded plugs with a non-grounded plug (two-prong) and then reverse it in the socket. This cured the hum AND led to a shock-free pairing. (There hadn't been a shock problem before, just a hum problem.) The soundman called this "lifting" the plug. Lifting and reversing polarity.
Last Edited by on Sep 22, 2011 5:43 AM
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walterharp
702 posts
Sep 22, 2011
6:23 AM
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The grounding set up on 50's amps are not correct, and simply wiring a 3 prong plug to the amp with the third prong wired to the chassis is not necessarily correct and safe by today's standards. Make sure an amp tech who really knows their stuff looks at this. Listen to 5F6H on this, he really knows his stuff.
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chromaticblues
1012 posts
Sep 22, 2011
6:58 AM
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I use to work on only old amps and with some old amps just putting a three prong chord on isn't of much benifit if the chassis grounding isn't designed for it. What I mean is you can put a three prong chord on and it can hum like crazy still!
I think what Adam is refering to is the problem. Old amps and audio devices use to have a polarity switch. It was for the reason you've described.
So what that means to you is you have to change the two wires on the three prong chord around. One goes to the fuse and the other goes to the on/off switch.
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Bb
276 posts
Sep 22, 2011
7:31 AM
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Simple fix. Go wireless. :^)
-Bob
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http://www.facebook.com/home.php?ref=home#!/pages/Bourbon-Bleach/161722307208585
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5F6H
847 posts
Sep 22, 2011
8:25 AM
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The "death cap" (0.05uf) should be removed.
Massive please post a pic of the new 3 prong cord, the green wire must terminate at the metal amp chassis, remove any corrosion that may be hindering the connection.
Do not retro fit with a 2 prong cord unless you want to continue to be shocked. Yes, reversing the 2 prong plug will reduce hum & shocking likelyhood (this is what everyone did prior to 3 prong cords)...as long as you always plug it in the same way and the wall socket is always the same polarity (may not be).
Lifting the ground wire is illegal in many countries and will often result in shocks if the ungrounded device is used alone and you offer it a path to ground.
Be sure to confirm that any AC multiway sockets are also properly grounded. I always like to run the amp to it's own wall socket & find a long single point extension cord useful. All the SS stuff can go on the same multiway connector.
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www.myspace.com/markburness
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barbequebob
1746 posts
Sep 22, 2011
9:56 AM
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I started out in the 70's and amps never had grounded plugs as a general rule until much later in the daced and more often in the 80's and getting a shock was very common. The polarity switch was what you used and you just flipped the switch and that was it. In some amps, like the old Champs, what you had to do was to turn the amp and then reverse the plug because amps made prior to the mid to late 70's all were two prong and even PA's were like that as well. The one good thing about the reissues is that they all have the 3 prong set up now and if you see an early Bassman RI, the polarity switch is just a dummy switch because of the 3 prong setup.
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Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
CD available at http://www.cdbaby.com/cd/bbmaglinte
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LSC
92 posts
Sep 22, 2011
10:00 AM
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One other thought since you just bought it, unless your are positive the amp has been recently serviced by someone who actually knows what they are doing and you are very sure of it's electronic condition I would highly recommend getting it serviced by a qualified tech.
The Champ is a really simple circuit but my experience is that when it comes to truly vintage stuff you're better off going to someone with experience who is known in your community for their knowledge of vintage gear. A recent graduate of the Rock and Roll School of Technology is unlikely to understand the quirks of 60 year old equipment. Since you intend to use this amp as a gigging tool reliability is critical as well as the safety issue. A service will be under $100 and well worth it.
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LSC
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Greg Heumann
1279 posts
Sep 22, 2011
8:10 PM
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In my opinion, either the house system has two different circuits with significantly different ground potentials (unlikely if it was built in the last 50 years), the PA isn't grounded (unlikely) or some schmo failed to properly wire the 3 wire cord into your amp. There shouldn't even be even a question about polarity - there is a standard. Line side goes to the fuse holder. Neutral goes to the switch. That way EVERYTHING is protected by the fuse. This is how I wire all the Kalamazoo's I do. If the PA and amp are properly grounded - you will simply not get a shock. The shield on the cable to YOUR mic AND the house mic should be at ground potential.
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/Greg
Last Edited by on Sep 22, 2011 8:26 PM
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barbequebob
1747 posts
Sep 23, 2011
7:05 AM
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One other thing, is that the wiring is some clubs can be really funky and a freaking mess and all sorts of weird stuff happens, and if where you're plugged in if it's near the lighting, that can also be a problem as well. I've been in clubs where even some of the electricians who service them don't even know where some of the wiring leads to.
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Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
CD available at http://www.cdbaby.com/cd/bbmaglinte
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barbequebob
1748 posts
Sep 23, 2011
7:09 AM
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One other thing, is that the wiring is some clubs can be really funky and a freaking mess and all sorts of weird stuff happens, and if where you're plugged in if it's near the lighting, that can also be a problem as well. I've been in clubs where even some of the electricians who service them don't even know where some of the wiring leads to.
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Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
CD available at http://www.cdbaby.com/cd/bbmaglinte
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chromaticblues
1014 posts
Sep 23, 2011
7:23 AM
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Ah yes Greg you are right about that! I forgot all about that. It is VERY easy to do and should never be done any other way!
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LIP RIPPER
628 posts
Sep 08, 2012
9:01 AM
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Just did my recently aquired Zoo and it took less than a beer to install the new cord.
And what is a "death cap"?
LR
Last Edited by on Sep 08, 2012 9:24 AM
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Greg Heumann
1776 posts
Sep 08, 2012
11:50 PM
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Hey, Lip - you didn't just use a knot, or cable ties as a strain relief for your new cable, did you?
The death cap on the Zoo runs from the on-off switch terminal to the ground lug. Once you have an actual ground wire connected to that lug you can and should remove the cap. If it were to fail by shorting, you would have 110V on the chassis. Not good.
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/Greg
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tomaxe
31 posts
Dec 11, 2012
9:09 AM
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Hey guys
Searched the forum for this question and found this thread, so perhaps someone can shed some light.
2 recent incidents where I was shocked by the vocal mic while holding the harp mic occurred and I am trying to eliminate if there’s a problem with my amp or it was just bad luck in playing 2 venues where the main wiring was faulty. Usually I do not get shocked playing most venues, but I am usually close to our PA and am plugged into the same outlet/power strips as the PA. I have read this can make a difference.
My amp: Fender Bassman clone built from Weber kit by Sligo amps http://shop.sligoamps.com/. Amp is about 5-6 years old has had minor fixes done twice by a reputable tech once and by Steve from Sligo another time. So, I am assuming it’s wired safe.
PA is a modern 800 watt PA from Carvin. Has a phantom power switch which we have on most of the time because another band member uses a mic that requires it.
First time shocked was at an old VFW hall where a bandmate plugged my amp into a wall outlet while the PA and other amps were plugged into various chained power strips going to a wall outlet on the other side of the room. When I plugged my amp into a new power strip and included that into the chain of the other amps/PA, the shock was gone.
Second time shocked was an even older social club, and this time I was plugged into a power strip, but again in a different wall outlet than the rest of the amps and PA. Shocked again. This time, due to the size of the setup, I was unable to chain my power strip to the rest of the chain going to the other outlet without the aid of one of those orange extension cords, and it was a three prong female to 2-prong male. So similar to incident 1 but this time the variable was this orange extension cord. Still got zapped.
Is there a cheap way to make sure my amp is safe? Some sort of ground or voltage tester? If I can determine that my equipmant is safe than I can assume that either the PA is messed up or it was just the bad wiring in the mains of these two gig locations…
Any input appreciated. Love this forum! Thank you
Last Edited by on Dec 11, 2012 9:11 AM
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MP
2581 posts
Dec 11, 2012
12:49 PM
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great advice on fixing the problem from the usual suspects:)
but here is the rub. sometimes your gear and the PA are just fine but the The Three Stooges wired the club as BBQBob kinda/sorta impies.
i keep one of those foam windscreens for my SM-58 as quick fix insulation shock prevention. Works every time.
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MP
affordable reed replacement and repairs.
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click user name [MP] for info-
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