Audio - Eliminating earth loops

[JERD]

I have a friend that has a sound desk and one input to it is from an
electronic organ that produces a nasty earth loop (buzz) problem not 50
hertz mains.

Temporarily lifting the earth off the organs mains transformer completely
eliminates the problem, but this not a genuine or safe 'fix'.

I recall seeing an article in some electronic magazine some time back of a
240v mains unit that could be put in line with either the sound desk or the
'equipment' but can't now recall where I saw it!

Can someone please offer some suitable suggestions to rectify this problem?

A mains isolating transformer should do the trick, but am wondering if there
is some other cure?

jerd

 

[Phil Allison]

"JERD"

I have a friend that has a sound desk and one input to it is from an
electronic organ that produces a nasty earth loop (buzz) problem not 50
hertz mains.

Temporarily lifting the earth off the organs mains transformer completely
eliminates the problem, but this not a genuine or safe 'fix'.

I recall seeing an article in some electronic magazine some time back of a
240v mains unit that could be put in line with either the sound desk or
the 'equipment' but can't now recall where I saw it!

Can someone please offer some suitable suggestions to rectify this
problem?

** Best idea is to provide the organ with a balanced output connection.

Get one of these fit it inside the organ near the existing jack output:

http://www.altronics.com.au/index.asp?area=item&id=M0705

Wire the 10kohm side to the jack and the 600ohm side to a stereo jack or a
male XLR.

The ground terminal of the stereo jack or pin 1 of the XLR can be left
unconnected to eliminate ground loops.

The signal from the transformer can now be fed into a mic input or line
input on the audio desk.

A mains isolating transformer should do the trick,

** The organ already has one of them.



..... Phil

 

[Mr.T]

Even cheap DI boxes have a ground lift switch, which leaves the instrument
grounded, but isolated from the mixer ground.
Have you tried that yet?

I've used an isolating audio transformer (10K / 10K) to solve this problem.
It's not ideal quality wise,

Why not, good quality audio transformers are routinely used in pro audio,
and don't cost the earth.
Studio quality is more expensive, but unnecessary in this case.

but an electronic organ sound isn't going to
suffer unduly from the degradation.

That's for sure.

MrT.

 

[Phil Allison]

"Bruce Varley"

I've used an isolating audio transformer (10K / 10K) to solve this
problem. It's not ideal quality wise, but an electronic organ sound isn't
going to suffer unduly from the degradation.

** Long as the 10k to 10k tranny is installed at the receiving end on the
link - the signal quality is normally fine.

The little trannys in a metal can sold by Altronics ( M0705, M0706 etc) are
a good example.

Better to not mess with the mains side if you can avoid it IMO.

** Very few keyboards these days would use a mains earth connection, they
mostly either use plug-pak adaptors or are of "double insulted"
onstruction - so the one alluded to by the OP must be nearly antique.


...... Phil