amplifier humming (again)

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bohl1076

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southern california
good morning,

i went to my friends home recording studio yesterday to try to trouble shoot his ground looping issues. heres what i found-
the room is on its own circuit, one of the receptacles is a "half hot" with 2-3ways switches, so i went into the switch box, one of the romex had no ground looks like someone had cut it back, the other switch's gound wasn't connected to any other circuit,and it wasn't the home run, so everything else was grounded except that switch but other then that everything appered to be isolated from any other circuits and their grounds. at the panel i couldn't locate any ground rod or cold water bond, although i'm pretty sure it's grounded some where. there was a #8 or #6 aluminum from the ground bar going somewhere inside the wall (cold water? rebar?)
he told me it happens reguardless of what room he has all his gear set up in. i also noticed everything he had wasn't "radio shack quality", but pretty high end stuff , and i asked him if he uses that same eqiuptment when he plays shows, and he said he does use the same stuff (on tour or at shows) without any problems
any thoughts or suggestions?
thanks,
john
 
i got it now i didnt see your earlier post....i know you stated that there were no flurescent lights but what about other "noisy" components such as dimmers or fan controls on that same circuit..you said the room was all one circuit..did that include lighting?
 
John, try killing other circuits one at a time, or start with them all of and turn them on one at a time, while hearing the hum.

If you still have hum with no other circuits hot, you have a system problem. Maybe he uses different canles on the road.
 
....one of the romex had no ground looks like someone had cut it back, the other switch's gound wasn't connected to any other circuit,and it wasn't the home run, so everything else was grounded except that switch....
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Sounds like even though you may have ground wires present, there is actually NO ground at all..since you mentioned the home run doesn't have a ground wire. If that is the case, all the other interconnected grounds are simply making a giant antenna which is "backfeeding" hum through the audio gear's grounds. Not a good situation, and potentially unsafe.

...at the panel i couldn't locate any ground rod or cold water bond, although i'm pretty sure it's grounded some where. there was a #8 or #6 aluminum from the ground bar going somewhere inside the wall (cold water? rebar?)...
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Common practice in California in older homes was that the only ground was the cold-water line..or sometimes the rebar or a single ground rod.

Your best most economical bet to solve this is to run a dedicated, new circuit from the main panel to the studio room. Make sure the ground is attached at the panel to the neutral buss (which is grounded by the cold water bond, if it's intact.) Use NM cable and plastic boxes and don't waste time or money on IG receptacles.

I would also add at least one ground rod (better to do two) and bring the grounding of the service up to current Code.
 
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I have noticed that you haven't mentioned the equipment being used in the studio. Some things that might be considered would be the
  • Use of vintage equipment
  • Rack gear stacked on top of each other
  • High Gain Amplification
  • Gear cases made of metal or aluminum
  • Cable connections
  • Digital or Analog recording method
  • PA method employed

What I have found from looking around on some audiophile forums is that the most suitable component for audio line galvanic isolation is audio transformer. Secondly, balancing the line and removing of humming in PA systems instrument connection can be achieve too by using passive DI boxes, available at your local music stores.

Commercial products
Xitel Ground Loop Isolator - RCA isolator
Biltema 31-441 Galvaaninen erotin - RCA 1:1 audio isolator
Cordial CLT 1 - 600/600 Ohm line-transformer for the galvanic separation of the sound signal - XRL connectors
Monacor FGA-40 (Best.-Nr. 06.4370) Ground Isolators - RCA 1:1 audio isolation with 10 kohm impedance
Jensen Transformers - company which makes audio isolation transformer and DI boxes - XLR and RCA connectors
Leon Audio Passive Direct Box - 6.3 mm jack to XLR with isolation
Lundahl Transformers XLR inline transformer units for breaking up ground loop in audio systems - XLR isolation and XRL-RCA adaptation, good quality professional devices
Radio Shack Ground LP Isolator (270-0054) - cost about $16US, RCA plugs, for car audio

Good luck with this issue. Keep us updated.
 
At a home studio last month(with lots of hum),we found 25 amps of ground/neutral current running through his house to his main panel with the main house breaker open.This was an electrical system problem.:)
 
i like the idea of shutting off all the other power circuits in the house and then turning them on one by one till you hear the noise. Even turn off the other half of his room if you have to. prolly some thingamajig backfeeding some noise.
 
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