I used the Radio Shack ground loop isolator with great success when connecting my church's audio system to a computer for recording services.
Prior to the installation of the ground loop isolator, we got a bad 60-cycle hum, not only at the Linux recorder, but back into the sound system.
On another note, what is the recommended type of cable and method for running audio to an external antenna mounted antenna?
I need to run about 60 or 70 feet of cable from my "studio," to the basement, out through the wall, up the outside wall, along the eaves and finally arriving at the transmitter.
My power will be available at the antenna.
The simplest and most inexpensive method would be two-conductor speaker wire.
I've read a little about a balun or audio transformer installed at the source and target locations that allow for using two-conductor wire, however, that would increase the cost a bit.
I may try a radio link using a baby monitor transmitter/receiver I modified once for listening to computer audio around the house. However, I would lose the hi-fi sound that the AMT3000 offers.
Thanks,
Scott
Scott,
Audio should be sent to the SSTRAN transmitter via shielded audio cable. However twiested pair (like CAT5) can be used if your audio source has a relatively low output impedance such as is the case for the headphone output of a computer. Most audio line outputs of mixers, etc, actually have relatively low output impedance, so they can be good too.
With twisted pair, be very careful to look at the wire colors and be absolutely sure you are connecting ground-ground and signal-signal. Reversing the connections will cause problems.
Regardless of whether you use shielded audio cable or twisted pair, you can still experience ground loop problems. A ground loop isolator (like the Radio Shack unit) is simply a 1:1 transformer. Any other connection that includes a transformer in the path will do the same thing.
Ground loops are hard to visualize. The basic problem is that a small AC current can flow between your grounded audio source (computer or other 3-prong-plug grounded audio equipment) and the antenna ground because of the difference in ground potential between the house AC ground and your antenna ground.
The first line of defense (as has been said previously) is to connect a wire from your antenna ground system back to the ground rod at your home AC service entrance. This will eliminate the difference between AC power ground potential and the antenna ground potential. If this doesn't work to your satisfaction, then try the RS ground loop isolator.
The antenna ground wire doesn't actually need to be connected directly to the AC service entrance ground rod. You can run the wire into you breaker box and connect it to one of the neutral bus bar terminals. The neutral bus bar is connected to the ground rod, assuming your box is code compliant. You can easily check this by looking for the ground rod wire connection to the neutral bus bar in your breaker box.
Hi Phil:
Do you think this kind of two-conductor twisted pair would work?
Thanks,
Scott
Home Depot has what they call 'alarm wire' which is two-pair shielded cable with a fifth uninsulated wire. One pair is shielded and the other is not. For my cable run, I used the shielded pair for audio and the other pair for 12 volts. The fifth wire is ground and is grounded at the transmitter.
This wire is fairly inexpensive and can be bought in standard lengths or in bulk.
After all my changes and the isolator removing my hum im going to switch back to DC and audio all down the same cat5 line, cat five has a tendancy to sheild its self.. I will post my results..
Cat5 can be found with a sheild also, call oyour local network installer person or company to find it..
Im just using standard cat5 and it sounds good.. with the isolator in place.
Jason