Humming...

[tazman]

Well, I got my J99's back from Tim (he said they are working properly). I installed them in the chassis and I still get the humming between all the pres. As I turn the gain knob on the J99's, the humming changes or goes away. The humming is present in the A12's for the most part. My chassis consists of 4 A12's, 2 N72's and 2 J99's. Anyone else experiencing this problem?

Thanks,

Roberto

[tpryan]

Can you post a photo of the modules installed in your chassis?
Do you know anyone with an oscilloscope?

[tazman]

I will post a photo this afternoon. Yes, I do know someone with an oscilloscope. We actually used it yesterday to bias the N72's (I had not done that yet).

I switched order of the modules in the chassis and that made no difference. Basically I get a staticky/hum noise in the A12's, for instance, that varies when I rotate the gain on the J99's or other A12's, besides getting a pop for every gain click.

Also, when wiggling the wire harness, it makes noise as well.

This is like looking for a needle in a haystack

What should I check with the oscilloscope?

Thanks,

Roberto

[tazman]

Here is a pic

http://members.cox.net/rcerini/sca.JPG

One thing I have noticed. the ones that are affected by all this are position 3, 4 and 8 (namely A12, A12, J99). The pres are

1. A12
2. A12
3. A12
4. A12
5. N72
6. N72
7. J99
8. J99

I did more testing and it's really dependent on the wire harness, as I move it around, the hum changes in intensity and pitch.

After saving for nearly 2 years to buy these pres, I have gone from from feeling like a kid at Christmas to complete despair!!!

Thanks,

[tpryan]

That looks reasonable, but you really ought to neaten up the wire loops with a wire tie or two between each module. That's why we include so many.

So the modules at 3, 4 and 8 are noisy, but the rest are quiet? Can you describe the complete signal chain you're using for listening tests?

If you have an oscilloscope, try probing the output of one of the noisy channels to see if you can find anything that looks like a sine wave. Let us know what you find.

[tazman]

I did some additional tests. The noisy modules are not always the same ones, it depends on the wiring harness.

I am sorry to say it, but I give up!!! I want these to work. I was hoping to use them on some recording sessions and have not been able to.

I sent you an email about an RMA.

Thanks for all the help,

Roberto

[tazman]

I tried a couple more things.

Question:

It seems if I unplug the power from the J99's all gos quite. One thing I tried is to change the jumpers on the J99's to ground to chassis instead of power. This so far seems to have helped. Is that an ok solution?

Thanks,

Roberto