G7 PSU Hum question

[jrmintz]

I'm having a hum problem with my G7 PSU. I suspect a bad rectifier or the TL317. I found an intermittent short that I've corrected and I need to check the components now. Here's my question: the hum is apparent from the supply with nothing plugged in, though pretty soft. When just the cable to the microphone is plugged in with no mic the hum is MUCH louder. Why is that? Is that telling me something?

Thanks.

 

[gyraf]

Please define "hum"..?

I suspect you mean mechanically?

That would be a property of the used power transformer. More mech. hum with just cable connected points to something shorted within the cable. check, check, and double check..

Jakob E.

 

[jrmintz]

Sorry, Jakob, I should have been clearer. It's electronic, not mechanical. I think it's 120 Hz, but I'm not totally sure. Would the cable be acting as an amplifier? I definitely need to check more.

 

[gyraf]

..the interesting question is: how does it behave with microphone mounted? If there's no mic, then there's no termination of the mic signal lines, so they'll act like antennaes...

Jakob E.

 

[jrmintz]

It's fine with the mic mounted. I guess my hum was the intermittent short. One end of the 10K resistor was too close to one of the 10K resistors. Thanks for your help Jakob.

:thumb: