Why does an amp make a 60hz sound when I touch the input cable?

[Austin]

I always wondered this, when you unplug your guitar why is it that it makes a 60 hz or 120 hz or whatever noise by touching the cord tip? Might be a silly question but I want to be clear on this. In Europe it would be a 50hz or 100hz noise? It makes that noise even when using a battery powered amplifier so what is the reason exactly?

[frus]

because your body is an antenna for picking up noise, and then you connect it directly to the amp
note when you touch the ground (on the cord sleeve or the amp faceplate or wherever), the noise becomes quieter

that's why the guitar bridge and strings are grounded, when you touch them (and you usually do when playing), you radiate less noise from your body to the pickups

[Austin]

So if I built a room sized faraday cage in my house then it would no longer hum that frequency if I touched the cable end?

[frus]

well your amp would still have to be powered obviously so there would be some hum, but much less, yes

[Steve Conner]

You might also like to try it in "a van down by the RIVER!" with a battery powered amp, you should get no hum.

Unless there happens to be some power lines nearby. Or if the engine was running you would get ignition crackles and alternator whine.

[DrGonz78]

And you might be forced to eat a lifetime supply of Govt. Cheez!!! Hum is only subjective to your battery powered ways, but one can only wonder why they are picking up some Ranchero Mexican radio station at certain locations! Basically you are running around w/ an unbalanced guitar cable and your guitar as a radio antennae. Now if you have a battery powered amp that took a XLR balanced input of something you wish to amplify, then that would help reduce most Country stations, but the Ranchero is there to stay. Order me a marg and some tacos!

[Enzo]

As they all said, you are surrounded by 60Hz fields, it is everywhere unlessd you go out in the middle of nothing on battery DC. That is why your cords are shielded instead of just wires like a speaker cord.

In fact I always wanted to do exactly that experiment - amp on battery out in a field - just to see what I DID pick up in the absence of 60Hz.

[Tom Phillips]

Try the battery powered guitar amp next time there is a local power failure. The lack of hum & buzz is very impressive. The performance of a battery powered AM band radio improves significantly too as many distant stations are no longer obscured by the 60 Hz radiation.

[Austin]

These are all really great replies thank you..

Steve funny you mention that as I really have been thinking of making the back of my step van into a faraday cage, it wouldn't take much with no windows and all..

DrGonz78 and Enzo, I was kinda curious what sounds might come out of there outdoors in the absense of the stray electric field too.. Who knows?

[rjb]

You might also like to try it in "a van down by the RIVER!" with a battery powered amp, you should get no hum.

Would you need a grounding chain on the van?

[frus]

you could just connect the amp ground to the van chassis

[Austin]

Makes one wonder what effect the 60hz frequency really has on us since we are bombarded constantly with it even from the time we are in the womb.

Frus, if I understand correctly, to make my van a proper faraday cage I would need to completly enclose an area in there in metal with no gaps at all and then drive like a copper or some metal rod deep into the ground with a hammer and attach a ground strap to the van chassis and then it would get no radio waves at all in or out. The outside radio waves would shunt to ground and any radio waves emitted inside there like wifi or a cell phone etc would I believe just bounce around in there until they decayed? Can any of you engineering types validate this?

[Enzo]

Would it really even need to be earthed? I think of a guitar with wireless transmitter pack. As long as the guitar itself is shielded and has a shielded cable to the pack, no hum results, other than what would anyway. We don;t need to run a ground wire up to the guitar.

[Enzo]

Bombarded with 60Hz. Aside from wondering how far it penetrates flesh, I have to look at the statistics. SInce 60Hz entered our lives, we now are healthier, live longer, and even are taller on average. No causality implied, but it doesn't seem to have set us back any.

[J M Fahey]

I can answer this one, because I *did* test it .
I made a Ton (hundreds) of "MiniFahey", my take on the Pignose market, only improved.
9V from 6 "C" batteries, a real high impedance input preamp, pull boost/distort volume pot, 6" speaker.
Did I mention AC187/188 Germanium outputs?
When on my Band Touring days, we often stopped in a road, in the middle of nowhere, surrounded by corn/wheat fields or mooing cows.
I always made fun at musicians by telling them "touch the tip of the plug to check it works" and ..... *no* hum, just a click (static charge of his body).
I then made ugly faces and said "sh*t!! it's dead!!! what will you play with now in this long boring trip?"
And then recited an unintelligible invocation to Musician's God or whatever and said "ok!! plug your guitar, it will miraculously work again!!"
Which of course it did.
Oh, I miss those funny days !!!