Re: Iso Transformers


"Dale Farmer" <dale@xxxxxxxxxxxx> wrote in message
news:P1Uug.9418$PE1.7388@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

There is a lot of misunderstanding out there about power in our sorts of
situations with inducing noise into audio and video circuits.

The real root cause of much of this is actually a design fault in the
equipment. Known usually as the Pin 1 problem. ( Read AES-48 for a much
more technical and accurate explanation.) Basically when you have
equipment that is plugged into different power centers, say a mixer board
out at FOH and the amps sitting under the stage, you have the potential of
having the grounds at different voltages compared to each other.
That power in the different grounds will want to flow in one direction
or the other. this flow in the signal ground conductors is known as a
ground loop. This current will inductively add noise to the signal in
unbalanced lines, usually video or low end audio lines. It also flows
through the circuit boards of the gear at each end if the gear has the pin
one problem, inducing *lots* of noise in the affected gear.

You can put signal isolating transformers in the signal lines
(Humbuckers and so on) which block these ground loops. You can break the
safety ground on the power cable, which is a very bad idea, sometimes in a
darwinian fashion. You can stop using gear with the pin one problem.
You can add additional ground conductors that route that unwanted current
away from the sensitive signal electronics.

I'll go on more in another post, my dinner is calling me.

In balanced lines it is sometimes possible to disconnect pin 1
and fix the problem. IIRC pin 1 in most audio lines is just a shield
and doesn't carry an audio signal so it really only needs to be
connected at one end.

David


.

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