Is all, at least 95%+, 60hz hum from ground loops or is any significant portion to due some type of radiation? I have a significant amount of hum in my amplifier even though I have turned off almost all electronic devices without any reduction in um. The florescent light is significant if the amp or guitar is near it and it is on.
All I can think of is that there is some relation between the guitar and amp as the closer the guitar is to the amp the louder the hum. With the guitar unplugged the amp is very quiet. All I can think of is that the pickups are picking up radiation from the power transformer. Any other possibilities?
What can be done about this? The transformer has a metal case which should act as a shield? Also, what would cause the amp to radiate 60hz hum? The only non-audio ac that exists is before the rectification and at the heater filaments. How does the 60hz get radiated? I do realize that wires can emit radiation through changing electric fields but surely the strength should be quite low? The guitar still picks up the hum pretty loud 5 feet away.
What can I use to shield the hum? A thick copper or steel case around the amp?
** Magnetic radiation is the MAIN cause of hum in audio systems.
It is also the underlying cause of ground loop hum.
** Fluoro tubes generate a strong electric field buzz and some magnetic field hum from the ballast choke.
** Electric field hum is generated by any mains wiring, either power or lighting that is not shielded.
** Many guitar pickups ( ie single coil types) are the most sensitive devices known to man for detecting audio frequency magnetic fields in the local environment.
** The only fix is to buy new pickups that are dual coil and humbucking - and make sure the pickups are fully encased in metal covers and have shielded output leads. All wiring in the guitar must be shielded, the strings must be grounded.
The technique was known and used by Gibson as far back as 1955.
Just magnetic radiation of the mains transformer, picked up by the coil of the magnetic pick-up of the electric guitar. Solution? Better pickup element (humbucker), greater distance between guitar and amp. Better mains transformer (Ringcore). Jo
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Oh, Electric guitar. An electric guitar and associated amplifier, with its magnetic pickup and high-impedance unbalanced electrical connection, is suceptible to just about ALL possible sources of hum.
But if you have nothing connected to the amp but your guitar (and maybe some battery-powered stomp boxes in between), it's NOT a ground loop problem. If you've got anything else connected to the amp, disconnect it and see if that improves the situation.
The flourescent light could be generating it by induction from the ballast coil to the guitar pickup, or by radiation to either the guitar, the amp, or the cable between them.
Exactly. If it changes with position or distance between guitar and amp, it's the power transformer generating a magnetic field that gets picked up by the guitar pickup.
Yes, other things can cause problems but from your description the magnetic "radiation" is surely the main culprit.
As for other possibilities, does the amp have a three-terminal power plug with a ground pin? (this is for USA, not sure what the outlets are like in other countries) Does the ground pin actually plug into a three-prong outlet with the ground pin properly wired up?
Get one of these (not neccesarily this exact device from Harbor Freight, but any equivalent outlet tester):
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and plug it into the outlet to help answer that last question.
If the answer to either of the questions above is "No" then not only could it add to the hum you hear, it could be dangerous. Have that fixed.
As others said, humbucking pickups will help, but humbuckers give a different tone and some guitarists may insist on the single-coil sound. I've seen a way to put a "dummy" coil with no magnet in a Strat (or any guitar with single-coil pickups) to cancel stray magnetic fields without changing the tone - this search URL looks promising:
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Yes and no. A steel case will shield some of the magnetic radiation, but not a lot of it. To do that, you need a shield of mu-metal which is quite expensive.
Replacing the transformer with an equivalently rated toroid transformer would help a lot, but that would also be expensive.
You're right, the magnetic fields from the wiring is very low. If it gets louder as you move the guitar closer, it's surely the power transformer.
That sounds like a lot further effect than I've seen. Equipment (guitar amps, older synths, anything with a 60 Hz power transformer in it) generate 60Hz magnetic fields that tend to drop off rapidly between 2 and 4 feet or so. If you rotate the guitar (so the neck points at the amp or away from it), does the hum reduce? There may be an angle where it "cancels" fairly effectively.
Is the hum still there at much further distances from the amp, such as 10 feet away? If so, it's picking up 60 Hz magnetic hum from some other device's transformer (probably indicated by the level changing when you face the guitar different directions), or it's picking up radiated magnetic or electrostatic hum from somewhere (like a fluorescent light), instead of or in addition to the magnetic field from the amp.
In general, it's not practical to shield the amp, but perhaps it has a badly designed transformer. Have you tried a different amp just to see if it's any better?
** Last time I checked out a similar complaint - the guitar pickups were responding to radiated hum from the amp's tranny at a range of 10 feet or more. At a range of 2 feet the hum was VERY LOUD !!
Easy to tell, as the hum stopped immediately the AC switch was thrown, though the amp kept working for a second or two until the electros discharged.
The amp was a Fender " Hot Rod Deluxe" which HAS a copper flux shorting band fitted around the AC tranny, like most tube amps do. Thing is, amps like the above have HUGE amounts of gain available - such that a couple of MICROVOLTS of hum in the pickups is clearly audible through the speakers.
Thing also is, that NO hum is audible if you PLAY the damn guitar !!!
So, the simplest fix is to use a " noise gate" pedal in line with the guitar lead that mutes the signal when it falls below a preset level.
Test. Ground yourself. Then touch the strings, and or humbucker while you are experiencing the hum. Do so carefully, in case there is some juice wanting to pass through you.
What should happen (or not) is the hum should cease as soon as you clamp the guitar end of the circuit to ground by way of touching it.
If that indeed does happen, this is a ground loop problem. There is either an open shield somewhere or there need to be a shield on a cable that needs to have one end or the other opened.
I had an earth ground that I touched to the chasis and it reduced the hum significantly. I suppose the receptacle does not have a safety ground because there is no continuity between the earth's receptacle and true earth ground. I guess this explains why touching it helped the hum.
I'm still curious as to what is causing the hum. If it is simply magnetics then surely the transformer shielding should solve the problem? Even without it being gounded the magnetic path of least resistance is through the cover rather than out side of it?
You know Phil I don't always agree with you, but you hit a very good point here. I observe that a lot of "high end" equipment is being designed or built by folks who do not understand the evils of magnetic radiation or pickup. So we end up with power supplies with huge 120Hz current spikes to charge the oversized capacitors, or low-level circuitry without proper lead layout that is intrinsically sensitive to magnetic radiation.
Back in the 50's, economics usually precluded massively oversized DC filter capacitors, and only clueless newbies ran low-level signal leads in loops that picked up magnetic radiation. But today we have lots of newbies who can buy massive and cheap lytics, and also who don't know how to keep the area in the important loops small.
The best consumer designers know to avoid these problems, undoubtedly from the school of hard knocks. It's the "high end" or at least "low production" stuff today that seems to be designed by the clueless, never sold anything before designers.
You've already spotted the problem - the fluorescent lamp. If it's absolutely necessary that the area needs to be lit, then put the lamp in a Faraday cage made of hardware cloth, and ground it to the frame of the lamp, which is grounded to the 3rd (green or green/yellow, depending on pondedness. If that doesn't fix it, then replace the lamp with incandescents.
If the lamp was off while you were doing the rest, then never mind. ;-)
That is where the AC line gets INJECTED directly into the amplification loop through a ground path that is shared by the chassis ground. These grounds are usually kept separate for this very reason.
It has nothing to do with magnetics because it happens on an SMPS fed system as well.
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