Buzz that stops when i touch input jack

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formulaq
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Buzz that stops when i touch input jack

Post by formulaq »

So i posted a few weeks ago about putting a 12at7 in my vox ac15. I ended up putting an EHX 12ay7 in. The Tone sounds great, huge improvement in my opinion. However before i replaced the tube and now still there is a dull, consistent buzzing noise that is way more prominent in the top boost channel of the amp. Turning on the tremolo affects it, turning up the volume/treble makes it worse. The buzz however is significantly reduced if i touch the input jack on my guitar , or either of the pickups. The guitar is a taylor solidbody using mini humbuckers. The buzz is still there in both full humbucking positions, but i find is the worst in the middle position:(Position 3: Full neck pickup with the inside coil of the bridge pickup (adds fatness and drives the amp a little harder for extra crunch)) and quitest in the 2nd position:(Position 2: Inside coils of the neck and bridge pickups in parallel (skinny, funky neck tone). The other 3 positions have an almost identical level of buzz.

Also even before i plug my guitar in, but just plug a cable into either channel, the buzz is there just a bit more muffled/quiet.

Edit: Also notable that there is no noise whatsoever in standby, it only starts when i switch standby to on, and it kind of starts off quiet and gradually increases in volume over 3-4 seconds. I was reading another thread where i can pluck out the preamp tubes 1 by 1 with the amp on to isolate the noise, this is safe to do, right?

Does anyone have any idea what this could be? Thanks so much.
Last edited by formulaq on Wed Dec 24, 2014 3:28 pm, edited 5 times in total.
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cbass
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Re: Buzz that stops when i touch input jack

Post by cbass »

Could be a bad tube leaking voltage to the grid. Is your guitar volume scratchy?
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formulaq
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Re: Buzz that stops when i touch input jack

Post by formulaq »

No, the guitar tone/volume all sounds pretty good when im playing, its more evident when im not playing , or even without the guitar plugged in- just a cable and the amp turned up. Im starting to think its just inevitable amp noise...but im still not so sure.

Edit: Could be a bad cable? The weird thing is a just bought a new 6ft monster cable and the noise is SIGNIFICANTLY worse when using that cable as opposed to the old fender one i had before. The monster cable has no plastic/rubber coating just beneath the input plug...dont know if thats why but yeah.
kgreene
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Re: Buzz that stops when i touch input jack

Post by kgreene »

Sounds like it will be something related to the power supply. I would seriously look at the ground issues. Next, I would be suspicious of some component or part of the circuit that is acting like an antenna.
KG
kgreene
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Re: Buzz that stops when i touch input jack

Post by kgreene »

BTW, if your amp is on and turned up, with a cable in the input, and the guitar unplugged, you should get a very big noise, if everything is working right.
KG
pdf64
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Re: Buzz that stops when i touch input jack

Post by pdf64 »

How about with a different guitar? Perhaps the strings aren't grounded on the Taylor.
R.G.
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Re: Buzz that stops when i touch input jack

Post by R.G. »

Is this by chance a two-wire power cord?

Sometimes a two-wire setup or a three-wire with an open/high resistance ground lead will let through RF buzz that mimics hum and changes when a human body touches ground.
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johnnyreece
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Re: Buzz that stops when i touch input jack

Post by johnnyreece »

R.G. wrote:Is this by chance a two-wire power cord?

Sometimes a two-wire setup or a three-wire with an open/high resistance ground lead will let through RF buzz that mimics hum and changes when a human body touches ground.
Yeah, I have something like this in a room of my house that the ground connection isn't actually connected to ground. When I plug in, I get a bit of noise unless I am touching the strings. I always attributed it to my computer being on the same circuit/in the same room until I actually tested the socket. Now, if I'm checking for noise, I go elsewhere to play.
R.G.
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Re: Buzz that stops when i touch input jack

Post by R.G. »

johnnyreece wrote: Yeah, I have something like this in a room of my house that the ground connection isn't actually connected to ground.
ACK!! QUICK! CALL AN ELECTRICIAN!

That's not an annoyance, it's potentially deadly. Hook up the wrong slightly-defective bit of equipment and grab the wrong thing and you, too, can experience 60-Hz-induced ventricular fibrillation. :shock:

If you're renting, even better, the landlord has to fix it. But even if it's you paying for it, electricians are cheaper than funerals.

When the subject of AC power line safety and grounding comes up, I tell every musician I talk to about it to go get one of those $5-10 safety test plugs from Lowes or Home Depot. They plug into an outlet and tell you if it's wired right. If it's not, you at least know before you get shocked.
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johnnyreece
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Re: Buzz that stops when i touch input jack

Post by johnnyreece »

R.G. wrote:
johnnyreece wrote: Yeah, I have something like this in a room of my house that the ground connection isn't actually connected to ground.
ACK!! QUICK! CALL AN ELECTRICIAN!

That's not an annoyance, it's potentially deadly. Hook up the wrong slightly-defective bit of equipment and grab the wrong thing and you, too, can experience 60-Hz-induced ventricular fibrillation. :shock:

If you're renting, even better, the landlord has to fix it. But even if it's you paying for it, electricians are cheaper than funerals.

When the subject of AC power line safety and grounding comes up, I tell every musician I talk to about it to go get one of those $5-10 safety test plugs from Lowes or Home Depot. They plug into an outlet and tell you if it's wired right. If it's not, you at least know before you get shocked.
Yeah, I went the easy route and decided to not use that one anymore. :lol: That's exactly how I determined that it was ungrounded, though; the cheap-o safety plug checker. Ah, 1950's wiring...
formulaq
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Re: Buzz that stops when i touch input jack

Post by formulaq »

R.G. wrote:Is this by chance a two-wire power cord?

Sometimes a two-wire setup or a three-wire with an open/high resistance ground lead will let through RF buzz that mimics hum and changes when a human body touches ground.
what do you mean by two-wire? it has 3 prongs, including the one for ground. It has done the exact same thing on various outlets in my house.


I've replaced all 3 preamp tubes, and the actual guitar tone itself it fantastic. At this point, im ready to just rig a setup that tapes a cable from the input jack on the guitar onto some part of my body (haha) I dont really know what else to do, touching the electronics on the guitar basically completely stops the buzz and i dont feel any electric shock whatsoever.
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johnnyreece
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Re: Buzz that stops when i touch input jack

Post by johnnyreece »

Have you checked to be sure the outlets of your house are properly grounded?
R.G.
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Re: Buzz that stops when i touch input jack

Post by R.G. »

Sometimes the entire house ground gets high impedance. A loose wire in the main breaker box can do this, as a single point of failure. It's rare, but happens.

An even more dangerous situation can happen - a high impedance neutral wire back to the power-pole transformer. When this happens, the two halves of the 240V power distributed to the house get unbalanced by loading. A dryer, electric oven, or even a household clothing iron can make the "120V" low on its half of the 240V total and correspondingly the other half well over 120V. This can start fires.

The better socket testers may pick up high-impedance neutral. But if you even suspect a problem with the house wiring, call an electrician.
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TUBEDUDE
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Re: Buzz that stops when i touch input jack

Post by TUBEDUDE »

At a minimum install a GFI outlet where you plug the amp in. Even with a wonky/missing ground the breaker will trip if it sees 5mA of difference in current draw. But testing all your outlets and verifying valid low impedance grounds is paramount for safety.
Tube junkie that aspires to become a tri-state bidirectional buss driver.
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