hum -audio due to grounding?

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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
090128-1818 EST

You need to determine the origin.

Is it inductive pickup from inductive fields?
Is it capacitively coupled?
Is it from ground path current?

How do you determine the source. If I have an amplifier contained in one shielded box, supplied from a wall outlet, a speaker connected to the amplifier, no wires connected to earth or an EGC except the one grouind wire in the power cord, and all gain controls set to 0, then is there hum? If so it is an internal amplifier problem. You might need to short any microphone inputs for this test.

If in the above test there is no hum, then attach things and determine what causes hum. When you find the item that causes the hum, then determine why.

Bad filter capacitors in the amplifier should probably produce 120 Hz hum.

.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
How do you mitigate hum coming across audio, grounding problems?
Simply put, you have to make sure the various components' chassis have no voltage differences.

The biggest offender in a home can be the cable-TV shield. In commercial, it can be multiple circuits.


Tell us more.
 

Mule

Senior Member
Location
Oklahoma
090128-1818 EST

You need to determine the origin.

Is it inductive pickup from inductive fields?
Is it capacitively coupled?
Is it from ground path current?

How do you determine the source. If I have an amplifier contained in one shielded box, supplied from a wall outlet, a speaker connected to the amplifier, no wires connected to earth or an EGC except the one grouind wire in the power cord, and all gain controls set to 0, then is there hum? If so it is an internal amplifier problem. You might need to short any microphone inputs for this test.

If in the above test there is no hum, then attach things and determine what causes hum. When you find the item that causes the hum, then determine why.

Bad filter capacitors in the amplifier should probably produce 120 Hz hum.

.

Im impressed....!! good info :) I've played live music years and those pesty hums can drive you up the wall..... we just start unpluging stuff untill we find it..usually start at the DI box...
 

macmikeman

Senior Member
Well known brands of computers and printers are very common sources of AM hum. They are not supposed to cause interference, but they do sometimes. And best of all, if the houses are scrunched together like some places around here, it might not be coming from the house you suspect it is.
 
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