Noisy BA283

[craigmorris74]

I built a two channel BA283 for use as make up gain for passive EQ's and passive summing.  I used Igors BA 283 boards and a JLM TREX power supply.  I've used these for a few months with no problems.  Last night I noticed I that both channels were picking up noise that seems to be coming from my studio computer.  The BA283's are the only gear that I've noticed picking up this noise.  I can hear movements that I make with the mouse, that hard drives running, and both get noisier when I open an audio program.  Here are some other things I've noticed:

1.  The noise only occurs when I plug the amps something into the input.
2.  The noise only occurs when the inputs are connected to the a patchbay in a rack of gear closest to the computer.
3.  When I connect the amps to gear that isn't in that rack I've mentioned, the there is no noise.
4.  I plugged the BA283's into a power conditioner by themselves, plugged into a different outlet, and there was still noise.
5.  I plugged the computer into an outlet on a different breaker, and there was still noise.

Here's a link to a sample of the noise:
https://soundcloud.com/telecasterdc/noise

I'm confused as to why the noise suddenly appeared when I wasn't having any problems before.  Any tips or suggestions for things to try would be greatly appreciated.

 

[shabtek]

sounds like garbage being injected onto the mains/ground?
what kind of power conditioner?
is the computer on a conditioner or ups?

 

[craigmorris74]

Thanks for the reply.  The conditioner is a Furman PS-PLUSDM.  The noise was present if I plugged the amps in to it or a different outlet without the conditioner.  I haven't put the computer on the power conditioner, but did plug it into an outlet that is on a different breaker than the amps, and there was still noise.

 

[shabtek]

try a ground lift plug on the BA283 box and see if things change--might narrow it down

 

[craigmorris74]

Haven't tried the ground life plug yet, but tonight, after I checked the grounding inside the BA283's, I ran a few more tests to check things out.  I still heard the noise, but when I pulled the cord connecting the input to my patchbay out about 1/4", the noise went down dramatically.  I can't hear it in my phones at normal listening volume.  My DAW is showing -92 dB from the outputs.  Does this narrow things down any?
Thanks,
Craig

 

[shabtek]

i suspect there is a ground/shielding issue
where does pin 1 at the output connector go?

 

[craigmorris74]

The output connectors are metal TRS jacks.  Pin 1 of each output is grounded directly to the chassis.  It has good connectivity with the entire chassis.

Upon looking at the unbalanced TS inputs, Pin 1 is connected to chassis, and a wire also goes to ground on the PCB.  Could that be a problem?

 

[shabtek]

could be,
there is transformer balanced out yes?
try a cable that lifts pin 1 on the output

 

[craigmorris74]

Yes, transformer out.  I'm going to try lifting pin 1 tomorrow.

 

[craigmorris74]

Solved the problem.  Tried all the above suggestions, and nothing seemed to work.  I moved the EQ out of the rack it was in and put it in a rack farther from the computer, and that solved the problem.  Shabtek, thanks for all the suggestions.
Craig