line filter for guitar amps

[Dimitree]

hi everyone

I was reading this:
https://en.wikipedia.org/wiki/Line_filter
and I was wondering if they could be useful for guitar amp.

In particular, in my situation, I've got huge 50Hz hum from my amplifier when I'm not touching the guitar metal parts.
That does NOT happen if I use the SAME amp and the SAME guitar in another house.
So I'd say it's not the amp or the guitar's fault.

Can I fix it with a filter like that?
if yes, what kind of filter would I need?

ps. I live in Italy, and most houses here doesn't have a proper earth connection

[PRR]

The line filter won't stop 50/60Hz. (If it did, your lamps and amps would not work.)

Room-induced hum fixes invite DANGEROUS mis-connections.

[ashcat_lt]

The fact that touching the guitar fixes the problem also answers part of your question.  The hum is coming from you.   Perhaps more correctly it's coming from the wiring and/or other appliances in the room, being collected and focused through your body, and blasted into the pickups.  When you touch the strings, you "short yourself".  The hum is not coming from the amp itself.  The amp quite definitely has some pretty serious power supply filtering already anyway.

Shielding the guitar and/or using hum-cancelling pairs of coils could help, and sometimes quite a lot, but it's always about compromise with these things.

[amptramp]

Here is one tutorial on guitar shielding:

http://www.seymourduncan.com/blog/setups/how-to-shield-a-guitar

Here is another:

http://www.bestbassgear.com/ebass/repair/simple-guide-on-how-to-install-copper-shielding.html

The shield should be grounded to the shell of the output jack.  Note that you should ground the bridge as well, but ground it through a parallel combination of 220K - 330K resistance and a 0.01µF to 0.05 µF capacitor so you don't get connected directly to one side of the line when you touch the guitar strings.

[ashcat_lt]

The shield should be grounded to the shell of the output jack.  Note that you should ground the bridge as well, but ground it through a parallel combination of 220K - 330K resistance and a 0.01µF to 0.05 µF capacitor so you don't get connected directly to one side of the line when you touch the guitar strings.

Ahhh the "safety cap"...

It's much better to keep your amp well maintained, preferably modded to remove the "death cap" and include a proper 3-prong safety grounded power cable, and double check the mains wiring before you plug it in.  What protection that cap might provide is questionable at best, and you should not trust it with your life.  It will compromise some of the noise reduction you're currently getting from the bridge ground (low frequencies will "get through") and kind of just complicates things.

If you are putting one in, and you want half a chance at surviving B+ voltages, it should be rated for like 600V.  It should also be between all of the "touchable" parts and the jack sleeve.  This includes things like switch bodies (and levers), pot shafts, pickup covers, etc.  You still have to fear both the jack and the cable itself.

The only way to be absolutely sure that you won't get shocked from an amp failure or faulty house wiring is to go wireless. 

The late chrisK said it (and about everything else) better than I ever could here

[anotherjim]

Ah this old favourite.

If I touch a high impedance amp input I make one hell of a buzz.

If I touch a tube amp 320v HT I get one hell of a buzz.

Am I a noise source or a ground path?

Both of course. It depends on the rest of the circuit which part I play.

So, if touching the shielded parts of the guitar STOP the hum what role is the body playing?
I bet on ground path.

I would do my level best to get a grounded AC outlet to work with. Even if that means getting a ground/earth stake/rod (surprisingly inexpensive) and a coil of yellow/green earthing wire and adding one myself - or get a tame electrician to do it for you. Don't be tempted to tie the ground  to copper water pipes - can't be trusted as the supply pipe is probably plastic, although metal heating/water pipes should be tied to earth anyway.

"ps. I live in Italy, and most houses here doesn't have a proper earth connection" - You could shout at a politician/power company about that - a Safety Earth connection is part of EU standards and there could be EU grants to get them up to that standard (or there was, but the money seems to have gone elsewhere  ) - or it's the landlords responsibility if you rent.

[Vitrolin]

You could shout at a politician/power company about that - a Safety Earth connection is part of EU standards and there could be EU grants to get them up to that standard (or there was, but the money seems to have gone elsewhere  ) - or it's the landlords responsibility if you rent.

that only applies to new installations,and when changing og maintaining existing installations.
there is nothing that forces new installations throughout EU, unfortunately for electricians...
you can still legally have a house with those wonderful cloth "isolated" until you need to change something and call an electrician.

[PRR]

>> ...ground the bridge ..through a parallel combination of 220K - 330K resistance and a 0.01µF to 0.05 µF capacitor
> It's much better to keep your amp well maintained, ...3-prong

Jim is suggesting this cap *in the guitar*, only on the bridge/strings.

Amp caps is something else.

In many places in the world, grounding is not available at most outlets. I think this is a safety issue as well as a real annoyance for audio. But very few people have the knowledge and resources to modernize building wiring.

[GibsonGM]

I would do my level best to get a grounded AC outlet to work with. Even if that means getting a ground/earth stake/rod (surprisingly inexpensive) and a coil of yellow/green earthing wire and adding one myself - or get a tame electrician to do it for you. Don't be tempted to tie the ground  to copper water pipes - can't be trusted as the supply pipe is probably plastic, although metal heating/water pipes should be tied to earth anyway.

I'm not trying to nitpick, I know you're not in the US, but someone doing this should REALLY consult some good reference material on mains grounding, or contact a licensed electrician if there's a mains ground problem.  If the circuit is already grounded elsewhere, and YOU install another ground rod, you have just changed the relationship between the power distribution in the building and ground...like with our PCB's, there should only be ONE ground point.   

If you introduce resistance between multiple ground points, they may not function the way they should, and thus fuses etc may not blow when they should!      I bet you were referring to, as PRR also brings up, places that just do not have a ground at all...here, almost all DO, and playing with it can be a very bad idea...

[ashcat_lt]

Jim is suggesting this cap *in the guitar*, only on the bridge/strings.

Yep.  Then I suggested that if you're going to do it, you should isolate everything metal on the guitar that you might touch.  I also meant to imply that it only might help in certain specific situations, but you should not be trusting it with your life.

Really the biggest shock hazard we have is when we touch two pieces of equipment which disagree on where ground is.  Like when the FOH mixer is opposite polarity from your amp and you step up to sing and you think the lights are flashing but it's actually your eyelids fluttering, or your bassist is plugged into the outlet on the other side of the room and you pass him a joint.

This cap might knock down that bite, but proper mains connection is a much better solution.