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Old 09-23-2005, 03:41 PM
Scotty_OiArT Scotty_OiArT is offline
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Join Date: Aug 2004
Location: Toronto East
Posts: 156
Default Electrical Noise on Firewire Bus

Greetings all,

A Trouble Shooting Excersice And Hopefully Some Great Minds Can Chime in...

Gear :

-I have a g5 Dual 2.0 Second Generation, combined with a 002 Rack.
-A Pioneer Silverface Amp (HomeStereo Style) that is a real gem, provides amplification for my Farfields / Nearfields (switchable). This is connected to my 002R via Unbalanced, Rca -> 1/4 TS inserted into the Montitor Outs.
(As a Variable in this test I have also tried connecting to the -10db Unbalanced outs provided on the 002. No Difference)

Problem :

When the firewire cable is disconnected, or the Powermac is turned off, I can turn my Poweramp to full volume, and the only noise i hear coming from the Monitors are the typical Faint Hiss you would expect from 150w of power fed by an unbalanced cable. As Typical of the RCA's they will indeed pick up cell phone signal, Flourecent Overheads, or EMI from the refrigerator from upstairs, but all in all pretty quiet as indicated.

Now if you boot the Powermac, within seconds of initial startup tasks, (with amp still turned up to 2 oclock) you immediately start to hear high pitched noises, 8-14khz approx. and noises alter in accordance with movement of the mouse, a mouse click, or a keyboard command... literally as if you can hear the mouse tracking through the farfields. there are alot of noises in this signal so I am led to believe that it is a funky grounding issue, however, the noises are reduced exponentially by switching to the FRONT Firewire Port on my G5. This is not an acceptable solution though because the sounds are still present although much quieter.

If it is really nessicary I can record an example of this noise but i am sure others out there have heard it before. I know that i can probably eliminate most of the noises from my monitors by setting up a balanced monitor rig (new amp) however that basically is a coverup of the sound and does not at all address the real problem (noise traveling down the firewire cable)

This is the stock IEEE1394 Cable that shipped with my Digi002Rack.



Problem Part "2" :


This problem could possibly be solved with whatever solution is used for part A (above), however,
Whenever CoreAudio is launced and a connection is bridged between Digi002R and OSX a new even more annoying noise (i can hear both only this one is way louder) is produced that is audible not only through my monitors, but from the G5 itself (its like the noise is just coming from everywhere) A really high pitched mind drilling noise...

Affected Applications include : ProTools, DVD Player, iTunes, or anything else using CoreAudio


I thank you in advance for taking the time to delve into this problem
This may not be an HD Rig, but it should still be capable of Professional Results
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  #2  
Old 09-24-2005, 09:06 PM
albee1952 albee1952 is offline
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Join Date: May 2004
Location: Norwich, CT
Posts: 36,870
Default Re: Electrical Noise on Firewire Bus

For sure, your old Pioneer is not well sheilded due to its age and all computers generate a lit of RF so I would run long "quasi-balanced" cables and move the Pioneer 10 feet away or more. By "quasi-balanced" I mean: take a good pair of balanced TRS cables as long as you need, cut the plug off of one end and replace with an RCA plug wired + to tip, - to RCA sleeve, and no connection for the sheild. What this does is that any RF, EMI etc. that the sheild picks up, is shunted "upstream" to the 002.
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