Hum - FIXED (I hope)

[tazman]

For some reason, when I installed my J99's, they made the A12's in the enclosure hum like crazy and the J99's would hum as well. The hum would change depending on the J99's gain setting and it would change when wiggling the power harness.

I seem to have resolved this by grounding the J99's to chassis instead of power (J3 and J4 jumpered at pins 1-2 instead of 2-3).

This is puzzling as to why I have to do this, but nonetheless I think it may have cured them.

Out of curiosity, does anyone know or have a suggestion as to why this is?

Thanks,

Roberto

[tpryan]

I seem to have resolved this by grounding the J99's to chassis instead of power (J3 and J4 jumpered at pins 1-2 instead of 2-3).

Actually, jumpering J3 and J4 pins 1-2 connects pin 1 to power ground (PGND) and not chassis ground (CGND), but it's definitely interesting.

I suspect the symptoms you've been seeing are caused by self-oscillation, which requires some sort of feedback path that's been removed by changing the jumpers. It may also involve the load that's connected to the outputs, which is why we haven't seen the symptom here. Did you get noise even without cables connected to the J99s?

[tazman]

Yes, I believe the J99's were affecting the A12's even without cables connected to them. Interesting thing is that they never did seem to affect the N72's.

I also tried connecting the pres to my other soundcard (MOTU 896HD) via XLR-XLR cables and got the same identical results.

Could the way I have them jumpered now affect anything or am I ok?

thanks,

Roberto

[tazman]

Could the way I have them jumpered now affect anything or am I ok?

thanks,

Roberto

bump

[tpryan]

If it solved the problem, I'd say you're done. If you're curious, you can always scope the outputs to look for any ultrasonic oscillations.

[tazman]

Thanks Tim. As soon as I get a few minutes I am definately going to scope the output and see what all I get. I will post once I do.

Thanks again,

Roberto