[SOLVED] Question about ground loop isolator

[obrien135]

I have gotten some 60Hz hum on the audio system I am developing. One thought I had was to try an isolation transformer in series with the preamp. The problem is , the one I was able to find at radio shack doesn't have any info about the primary or secondary inductance or it's impedance at 1KHz or any other frequency. Therefore I don't know if my pre amp can drive it. The output of the preamp is a common emittor amp with a 2n3904 and a 1200 ohm collector resister. I read somewhere that some isolation transformers have an impedance of 600 ohms at 1KHz. That might be too low. If I understand correctly the impedance seen by the output would be the reactance due to the primary inductance in parrallel with the secondary inductance, all in parrallel with the reflected impedance. I don't know if the primary and secondary reactances would be low enough to be significant. How can I find an ground loop isolator that will work?

George

 

[john blue]

Your own audio isolator

 

[obrien135]

Thank you,and I looked into purchasing the parts in the future at Digikey. But the one at Radio shack would be a lot more convenient and not much more expensive. What are the chances that it would have an impedance less than say 100 ohms or so? If I did my calculations right, my circuit can handle a 75 ohm load.

I got a call back from Radio Shack and the applications engineer said that the impedance was 10Kohms. I didn't want to assume that this meant at 1KHz. It probably did, but I just wanted to make sure. He didn't know, but I guess if it at 10Kohms anywhere near the middle of the audio range , the impedance would be high enough for the amp I built to handle it. I'm probably going to give it a try, but I am open to other people's opinions.