How isolate two earths on electronic equipment?

Question

I am in the UK. I want to know how to reduce hum & buzz when connecting two items together.

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I have two pieces of electronic equipment (a PC and a tape recorder) that I want to connect so that a signal from the tape recorder is fed into the PC.

However if the two earths are connected then I get a buzz and hum. This does not seem to be induced on the screened cable because if I take the line output rather than the earphone output using the same length of wire for each then the line out is clean (but too weak to use).

The PC has an earth in its mains lead. The tape recorder has only two mains wires in its mains lead with no earth.

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I am told there are adaptors I can use in series with the signal lead which will stop the buzz & hum. I believe such an adaptor isolates the two earths from one another.

An example of such a product is the Retell (model 142) Connector.

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How does such a connector or adaptor work ???

Surely it's not simply a matter of cutting the earth lead such that it is no longer continuous between the tape and the PC ???

crazy frog · Accepted Answer

try 2 power diodes in parallel, with eachdiode conected as cathode to anode oneach end with a   .1uf greencap accross them.sometimes works, this seperates the mains earthfrom signal aerth.

sQuick · Answer

Whatever you do, don't remove the earth connection. This is not the way to fix the problem and could be dangerous.

Try disconnecting the screen of the cable at the tape end, this should fix it.

The line out from the tape deck should give a good signal when connected to the computer line in. If you are feeding the headphone output into the computer line in you are going to get noise & possible distortion.

sQuick.

crazy frog · Answer

the diode trick has this done in themarshall power amp 2/ch model 9200

crazy frog · Answer

the diode trick has this done in themarshall power amp 2/ch model 9200

bg · Answer

one chassis to another thru the shield of the cable. You have two options -connect a heavy ground strap from one chassis to the other to provide a pathfor ground current other than the shield. Disconnecting the shield at oneend will help.#2 - transformer coupling - this is what the adaptors do for you. Sometimesthey are called hum eliminators

n · Answer

If there is a radio shack, get a stereo isolation transformer.  They have RCA plugs on each end.  Used for cars that have a power amp in the trunk.  I use them from my PC to my home entertainment system.  There available by mail order too.  Cost is about $20 US.

How isolate two earths on electronic equipment?

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