How isolate two earths on electronic equipment?

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

--------

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.

----------

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.

formatting link

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 ???

Reply to
Sammy
Loading thread data ...

try 2 power diodes in parallel, with each diode conected as cathode to anode on each end with a .1uf greencap accross them. sometimes works, this seperates the mains earth from signal aerth.

Reply to
crazy frog

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.

Reply to
sQuick

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

Reply to
crazy frog

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

Reply to
crazy frog

So it is unlikely to be a ground loop - probably the headphone output amp has hum on it anyway - you should be using the line-out.

So why does the subject ask about isolating two earths? If /both/ pieces of equipment were earthed then you /might/ need to do something about the possible ground loop when adding a third connection between them.

You only have one earth.

Geo

Reply to
Geo

Your problem is called a ground loop. It is caused by current flowing from 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 path for ground current other than the shield. Disconnecting the shield at one end will help. #2 - transformer coupling - this is what the adaptors do for you. Sometimes they are called hum eliminators

Reply to
bg

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.

Reply to
n

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.