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'66 Vibro Champ hum

Discussion in 'Amp Central Station' started by kdmerchant, Aug 14, 2011.

  1. kdmerchant

    kdmerchant TDPRI Member

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    Hello. Wondering if someone has any experience with this situation. I have a '66 vibro champ that has a hum that is only bothersome when I take my fingers off the strings. It is improved somewhat by my HumDebugger.

    It has the original 2 prong power cord. Would putting a grounded 3 prong cord change this hum, possibly eliminating it? Could it make it worse?

    Thanks for your input!
     
  2. BobbyZ

    BobbyZ Doctor of Teleocity

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    Have you tried flipping the plug? The 3 prong is the best thing to do. May not help this hum but you won't get shocked as much. Also could be the guitar's grounding.
     
  3. StanV

    StanV Tele-Meister

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    The 2 prong cord has a "death" cap that may be going bad. Best to replace it with a three pronger. In the meantime try flippling the polarity of the two prongs around, meaning in you hand turn the plug 180 degrees around and plug it back into the socket. New two-prong appliances actually have a ploarity and one of the prongs is slightly larger than the other; in the old days it wasn't so.

    When you take the amp to get the plug replaced also ask the tech to check the ground.

    Hope that helps!


    BTW, I love the avatar!!! Looks like the "walrus" has gone missing!
     
  4. lowatt

    lowatt Tele-Meister

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    Dinah-moe humm
    Dinah-moe humm
    Where this dinah-moe
    Comin from
    Done spent three hours
    An I aint got a crumb
    From the dinah-moe, dinah-moe, dinah-moe
    From the dinah-moe humm
     
  5. kdmerchant

    kdmerchant TDPRI Member

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    I flipped the plug and the problem is solved. Thanks.

    KM
     
  6. alnicopu

    alnicopu Friend of Leo's

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    Still, go with the 3 prong plug and put the ground on the chassis somewhere. I usually go under a transfer nut. I had one back when I was a kid in the 70's with a 2 prong cord and it would give me a little shock when standing on a concrete garage floor, sometimes.
     
  7. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    Ditto - flipping the plug is a band-aid. Install a 3-prong plug and solve the problem (you'll still have some hum, especially if you play close to the amp).

    Sorta - don't want anyone to get confused.

    The one large/one smaller prong plug on all electronic equipment has been in effect for many years, but AC wall outlets (two prong) have ALWAYS had polarity. They just have not always been wired correctly.

    There is a hot and a neutral in every home's wiring Some older homes lack ground wires, which are either bare copper wires (non-stranded) on have green insulation. But "neutral" is NOT "ground".

    The biggest problem with older homes - I finally finished up mine, after 24 years of bit-by-bit analysis and work - is that many "kitchen electricians" figured AC meant the two-wire stuff with no ground, hence no polarity - and they wired homes (or additions) with NO regards to polarity.

    For a guitarist this can be deadly. If your amp is plugged into a 2-prong outlet wired one way and a small PA wired into something wired the opposite way, if you hold your string and grab a mic stand you'll get a nasty shock - often 57.5 volts, but sometimes the full 115.

    You'll also have hum problems galore, which is why I finally rewired my entire house - 3 prong outlets, green insulated ground wires terminated at TWO different places on the cold water pipe, and VERY close attention paid to polarity.

    If a light's not working or an amp is weak...or a hard-wired doorbell goes on the fritz, light switch acts up (and you have some 2-prong outlets in the house OR recently converted to 3-prong) if you measure the voltage it'll probably read 55-60VAC, leaving you scratching your head. The one that really drives most amateurs nuts is "I hooked up all 3 wires - why is it doing this?"

    Well, I guarantee if you plug an amp into one of the offending plugs and another into a "good" one, you'll read 50-60 volts across just the chassis' of the two amps with an AC voltmeter.

    Ever had a sort of "ticklish" feeling when touching equipment? It's the same thing but luckily something is shunting it to ground so you're not getting the full force.

    It can be very tricky and time consuming getting your home's wiring in order - but doing so (and elimination of fluorescent lights on any busses where you run your audio gear) will really reduce hum.

    Also - when you convert to a 3-prong plug there are a few things to be mindful of:

    1. Take the "death cap" (group cap) completely out of the amp so you don't confuse future owners. If it's there with a grounded plug it's confusing, and it has absolutely no safe use in a 3-prong circuit. If it's a vintage amp save the old cap (and 2-prong cord) for future owners; on a vintage amp with a ground switch unhook the switch entirely or use it for something else - a fixed/cathode bias switch, power reduction switch...but don't leave ground circuit wires on it).
    2. Pay CLOSE attention to the instructions (many are available on the web) and get the polarity right.Some recommend leaving the cap in place. DON'T use those. A few say it doesn't matter where the white or black wires go - IMHO those are written by idiots who think they know something they don't.
    3. Contrary to casual belief - Black=HOT; white= neutral, or "near ground"; bare copper or green=ground. This runs counter to many assembled products (including most amps) where black=ground.

    If you get one socket backwards it's guaranteed you'll get that tingly (and if a bad heart, a paramedic-summoning) 50-plus volt shock.

    Junction boxes and switches at each end of a hall connected to the same light are the worst in old houses - you have to trace every wire in and out (if wire-in-conduit was used you are in much better shape than if (cringe) Romex was used, which is like working on molded guitar cables.

    EVERY GUITARIST SHOULD CARRY A CIRCUIT/GROUND FAULT TESTER - A LITTLE PLUG-IN-THE-WALL GADGET FROM HOME DEPOT (OR ANY HARDWARE STORE ) FOR $7. IT CAN SAVE YOUR LIFE.

    Twice I've canceled gigs and gotten paid because power was was bad at a dumpy club. Power requirements are ALWAYS written into my contract, and I ALWAYS check.

    I got burned once - a well meaning but knucklehead sound "engineer" (I think he played with toy trains) had a hum problem in *his* equipment. He could not fix it, assumed it might be my amp and without notifying me installed a ground lift - The first song I stepped up to the mic, moved my hand to adjust it and woke up 15 feet away with mildly burnt hands. A ground lift is the "method of last resort" and should only be used by highly qualified technicians who know the risk and install isolation circuits. As far as I'm concerned the ground lift switch on most direct boxes should be taped or glued in the "off" position, since 90% of the users have no clue what it really means.

    So replace that Champ's power cord with a grounded one - the right way.
     
  8. kdmerchant

    kdmerchant TDPRI Member

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    Thank you for such a well thought out and informative reply. I will have a 3 prong plug put on by my amp tech right away.
     
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