Noise in Audio Out

[RJH_MUSIC]

I just rebuilt my music studio and moved things around a bit. I purchase a used second d8b cpu with mixing board and installed the compact flash with the 5.1 hack. Everything works fine.... well almost fine. Both CPU's to each d8b are located in a rack just below one of the mixing desks. The other mixing desk is located about 10 feet away. I am getting noise on the audio channels from the desk that is located just above the CPU's. The other desk is nice an quiet. If i crank up the master volume, the noise gets obviously worse and if i move the fader to -0- the noise is gone. The pitch and character of the noise sounds like the CPU cooling fan or the case fan. What is confusing is that this is the unit that has the compact flash in it which is located in the 3.5 floppy slot so I know it cannot be the hard drive noise. Is it possible i have the CPU to close to the mixing board or might there be something else wrong?

Thanks for your help.

I know the easy solution is to move the CPU unit and see if the noise goes away, but i just spent 2 months and a considerable amount of money making customer wall units to house everything and I hate to have to relocate the cpu.

[arjepsen]

one test could be to change which cpu unit powers which desk - switch the umbilical cords, and see if the problem follows the cpu unit, or the desk.
Can you switch those without too much trouble?

[Bruce Graham]

Hey RJH;

Another thing to try is to turn off all other gear other than the d8b & CPU in question and use headphones to eliminate the power amp. You may have already done this.

If the noise persists, check AC & Chassis grounding of CPU and Console. Make sure you have a solid ground.

Make sure all screws holding the Shield of the CPU are securely fastened as well as the screws on the desk. The EMI shielding should eliminate all noise coming from the CPU and inhibit EMI noise into the desk.

Do you have any un-shield cables entering the console? I know this is un-common, but some cables, with 1/4" connectors, are not shielded. The same for some custom made cables as they are built for Line level signal (+4dbu and above).

There is a "Filter" setting in the d8b that is used to reduce noise in channel 25 through 48. See if that is ON. It should be part of your startup file but since it is a new to you desk it may be off. This may have nothing to do with it but what the heck!

How clean is the power in your studio? Do you access to see an Oscilloscope to see the Sine wave and how pure it is.

Cheers
Bruce

[RJH_MUSIC]

Many thanks for the quick response. I will try a few more things. I am using 1/4" balanced cables throughout. I am particularly interested in checking the shield. I assume you are talking about the aluminum cover that goes over the Power supply section.

[Bruce Graham]

Yes. All the screws need to be secure.

There is a ton of "clocking noise" generated inside these beasts.

[RJH_MUSIC]

I a, also beginning to wonder if they is a connector problem in the desk because although BUS 1 - 8 outputs are connected and assigned, they will not operate. Which is why i am using the master outs.

[RJH_MUSIC]

"Beast" is definitely the right word! I do not know why Mackie made the thing that big and heavy. I guess that was the best technology we had back then. I keep saying that some day i will re-design it.

[arjepsen]

A note on those filter Bruce mentioned - I turned them OFF in the image I made.
If you like them ON, try that, and see if that gets you what you want.

[CarloLig]

A note on those filter Bruce mentioned - I need these electric log splitters and turned them OFF in the image I made.
If you like them ON, try that, and see if that gets you what you want.

What exactly do those filters do btw? I can't really tell.

[arjepsen]

I rhink they lower the background noise.
I always turn them off, since I feel they make weak signals behave erratically.