How isolate two earths on electronic equipment?

[Sammy]

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.
http://www.telephonerecorder.co.uk/recording/accessories/142.htm

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]

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.

 

[sQuick]

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.
http://www.telephonerecorder.co.uk/recording/accessories/142.htm

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 ???

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]

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

 

[crazy frog]

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

 

[bg]

Sammy wrote in message ...

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.
http://www.telephonerecorder.co.uk/recording/accessories/142.htm

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 ???

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

 

[n]

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.