We just moved into a 60 year old house and discovered that my daughter's
electric guitar and amplifier won't work properly. There'a a loud hum
coming from the amplifier. It stops when she puts her hands over the
strings, but starts up as soon as she removes her hands. Could this be a
grounding problem? Any suggestions? (There's nothing wrong with the guitar
or the amplifier. She also has a bass guitar and a bass amplifier and the
same problem is occuring with them too). Thanks.
As mentioned, this is a grounding problem.
It could also be dangerous, since if there's a fault in the amp the
guitar strings/various metal bits could become energized, which when
the ground works properly will cause the breaker to trip.
No ground, no tripping breaker!
Until you are sure everything is OK, it'd be cheap insurance to add a
GFCI outlet or breaker, or get one of those extension cords with a
Do you have a three pronged plug on your amp?
Were you talking about a grounding problem between the guitar and the
amp, or between the amp and the wall? I think it could be either, but
I'm assuming the guitar is like a turntable. (It probably is.)
If you meant the amp and the wall, you seem to know a bit about this.
I'm surprised you would plug a 3-pronged amp into a 2 pronged outlet,
so maybe the outlet has 3 openings, but the ground is no good there.
To find out, get a volt-ohm meter, or get one of those cubes with
three prongs and 3 leds and see if you have a good ground.
Let us know.
Is the amp power plug 3 prong/grounded?
Is there just 1 amplifier or is there more than 1 device plugged in and
Try reversing the way the power plug is plugged in (if it is not 3 prong).
Try using another outlet - preferrably grounded (kitchen, laundry?).
Try the above, but be warned that you may be flirting with unsafe
operation of the amp. Check the amp manual and or look at the
schematic to see if two 110v leads are double insulated. If not I
would stop using the amp with your unsafe outlet.
It's known as '60-cycle' hum, and is indeed a grounding problem. I don't
think it's dangerous, and there are a couple of ways to defeat it. The
first would only work if the guitar has two pickups, but reversing one of
them electrically will render the hum impossible (the theory behind
'humbucking' pickups). The next is to simply reverse the plug in the
outlet, which will get you back in phase.
This was the scourge of many a garage band years ago, but as you've noticed,
your daughter's touch gets things right back in phase. She won't get
electrocuted at the guitar either, because it's passive. The problem is at
the amp, and it's annoying rather than dangerous.
I suggest you perform a test on all your 3-prong electrical outlets and
classified them as grounded or un-grounded.
Using a $5 receptacle tester (those 3-prong thing with three lights) would
be a good start. If it says no ground, then you have no ground. If it says
normal, then it may be normal or someone may have connected a fake ground
(e.g. neutral) to the ground pin to pass the test.
Then, if you found some un-grounded outlets, consider adding a ground wire
or at least change them into GFCI.
This is a hassle but it increases the safety of your house, and possibly
make it easier to sell the house in the future.
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