Funny Buzzing fixed by touch?

one2manyhobbies

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Hi!

My name is Henry, thanks in advance for your help.

I am recording my nylon string guitar thru a KNA bridge pickup and there is a buzzy hum when I'm not playing. When I touch my computer or my TAC-8 interface, the sound goes away. So there is some kind of missing ground or something? Not sure how to fix besides paying my roommate to sit here with his hand on my interface while I record :) .

-H
 
Yes, this sounds like a ground problem. Are you using a laptop? If so, try running it off the battery instead of AC power.
 
Not sure how to fix besides paying my roommate to sit here with his hand on my interface while I record :)
Not sure that would actually help. I’m pretty sure the noise is coming from (or at least focused by) you. You’re the one that needs to be grounded. In an electric guitar that happens when you touch the metal strings which contact the metal bridge which is wired to the jack sleeve. You have none of that happening here, so you’ll need to find some other way to connect yourself to the circuit ground. I think the safest way is probably to wire up some sort of foot plate and rest your bare foot on that while playing. I’d ask you to not try to actually attach a wire between yourself and the device just on the off chance that ground path goes hot, you have a much better chance of survival if you can pull away quick rather than having to untie or unhook something.
 
Not sure that would actually help. I’m pretty sure the noise is coming from (or at least focused by) you. You’re the one that needs to be grounded. In an electric guitar that happens when you touch the metal strings which contact the metal bridge which is wired to the jack sleeve. You have none of that happening here, so you’ll need to find some other way to connect yourself to the circuit ground. I think the safest way is probably to wire up some sort of foot plate and rest your bare foot on that while playing. I’d ask you to not try to actually attach a wire between yourself and the device just on the off chance that ground path goes hot, you have a much better chance of survival if you can pull away quick rather than having to untie or unhook something.

No, do not ever purposely ground yourself for any reason*. This is especially important here as I am sure Henry's problem is a LACK of a ground in the system.

What is needed is an earth/ground wire from a metal part of the AI to true earth. A water pipe is good but a raditor might serve. You can use the earth pin on the mains outlet but be sure to get the right pin! You can buy "Earth plugs" in this country a 13A plug with a terminal or socket for the earth but no connections to live or neutral. I have looked but cannot find an example as yet.

A lot of audio gear, small guitar amps, active speakers, is now made with 'Class ll' insulation and needs no earth. This is a good thing as it avoids ground loops and is safer because if there is no safety earth, idiots cannot lift them! However, the problem is now that 'systems' can be built up with no earth at all and that causes hum.

*Yes, you can buy grounding 'cuffs' for anti-static electronics work but these ground you through at least 1 meg Ohm and are thus totally safe.

Dave.
 
I was going to say exactly the same thing as Dave. Grounds are there for more than one reason, and stopping hum is the most minor thing they do. Over the years - I'm surprised more musicians haven't died, but musicians are often the naturally lucky ones! when these topics come up, I look at my right hand - that's a burn from the edge of a radio mic receiver case - a gig in the late 80s with a well known band, who had removed their ground to get rid of some hums, but the radio receiver WAS grounded, and all I did was creep on stage and try to put back in a guitar jack that had tugged out. I reached over the back of the amp, grabbed the jerked out plug, in my right hand and as I went to plug it back into my hand, I brushed the receiver case, and it threw me across the stage. The scar is the result.

In fairness - most of these hums that vanish are because all the pickups by design contain components that work by magnetic coupling. Those that don't are often very sensitive devices doing lots of amplification and our environment is full of interference. Our nice flabby bodies are pretty good at damping all this, and providing screening and potential grounding (like the bare feet thing). Making to worse is leakage current. Grounds are rarely at ground potential. They should be, but they're not and if multiple grounds exist - which one is the right one? Connecting different systems by touch can restore this equal potential, but to do it, the current passes through your body. When it happens through your lips touching a mic, it tingles. Most times it's not dangerous because current is tiny and your lips are sensitive. However, like my scar - sometimes, perhaps rarely thank goodness, the current is a real fault. A broken turn in a transformer, a ground wire come off and touching a live component where it's been thrown in the truck once too often. In these cases, it's genuinely dangerous. I've seen people with mains power connectors and a cable coming out from the ground pin with a big car battery style connector on the end - and they attach this when things hum. It usually works of course, but one day they'll stick it on a metal jack on that faulty amp, and there will be a huge bang.

I suppose I'm saying that curing hums needs some knowledge of what you're actually doing to keep safe. Often, you can cure it, but have you? You solved the hum, but did you determine if it's a teeny fault, or an annoying coincidence and just equipment that hates other equipment, or something more dangerous?hands.jpg
 
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My Nylon Acoustic guitar does the same thing, I'm not saying it's the right thing to do but I got over the problem by using a DI box and resting my foot on it.

My house electrics are good according to the test sheet (as long as the readings are not faked). No humming on any of my equipment apart from the Nylon guitar! Have no idea why.

I am not bothered at all by it as I have on intention of recording my Nylon via DI again. It was just something I experimented with once.
 
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