Help. My MS20 is always humming!

[Dave Halliday]

>>What are you using after the line out?  Amp, cans, any amplification?
>>
>>There might be an ungrounded or poorly wired outlet causing a ground 
>>loop...  You might try a different part of the house ( sometimes 
>>outlets in the kitchen and laundry area are more recent than the
>>rest of the house )
>>
>>Or just deal with it until you get back.  Ground loops can get to the 
>>black art stage really quickly...  <g>

>     I find the simple way to deal with ground loops is to use cables with a
>     1k 1 to 2W resistor in line with the shielded ground wire, or to only 
>     connect the signal wire to the piece of equipment, but not the 
>     shielded ground wire. There was something on this in and old E&MM 
>     years ago. 


There are a couple of ways to go.

The single shield point works well - some mixers ( especially Sound 
Reinforcement ) and some amps will have ground lifting switches.

There are two types of GL switch - one will actually disconnect the 
third "grounding" pin of the electrical plug.  The other kind will 
disconnect the incoming shield from the input.  Either one works.

Transformers work great too except good ones are $$$ and cheap ones 
add interesting things to the music.

There are some iso ( isolating ) boxes which use OptoIsolaters but 
these are not perfectly linear.

For large concert venues, the trend is to use a fiber optic cable for 
the signal snake from stage to mixing position.  This cuts out a lot 
of induced noise ( RF and dimmers ) and Ground Loops, etc...



You can take care in your home studio to have all grounds come 
together into one point which is then tied to the houses electrical 
ground - this is called a "star" ground.



Fun thing to try to track down!  <grin>   I once worked for a public 
aquarium in Boston and two outlets near the front desk had a 40 Volt 
potential between the two grounds!
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