Isolating PC from sound system
by, 10-13-2011 at 08:15 AM (2223 Views)
I listen in a home office which has my music server and stereo, and also a PC for work/pleasure. Typically I'm at the computer and listening to music from the audio system.
Recently seemed that I'd lost volume (3-6db) in the stereo. Was turning the volume up a couple of notches more than I'm used to.
Couldn't figure out the problem, and then yesterday had to do some serious maintenance on the PC (reformat and rebuild the main C drive contents).
Anyway, this obviously entailed several shutdowns and reboots of the PC. And guess what? Every time the power on the PC went off, the volume of the music playing went up and clarity of sound improved. Every time I pressed the power button to turn on the PC again, the Volume/SQ decreased, and stayed that way until the next time the PC was turned off.
Immediately had a small panic, and started thinking about all the possible expensive solutions: Power regenerator for the Audio system, noise filters on the power lines, installing a separate circuit just for the audio, etc.
Then I talked to 2 friends who are electricians. They suggested 2 likely possibilities:
a)Power suck caused by some problem with the PS of the PC - the PC on its own, they said, doesn't usually draw enough current on a continuous basis to have that kind of effect(again, it wasn't just on PC startup, but for as long as the PC was on).
b)Noise in the system introduced by the PC. Either general electrical/circuit noise, or some kind of interference transferred over to the sound system. Said it may not be a "power drop", but just lower apparent volume caused by noise in the system. Asked if the PC was connected to the stereo. I said no. They suggested, among other things, using an extension chord and plugging the PC in on a totally different circuit in another room to see if that made a difference.
But when I got home, I suddenly realized that the PC WAS directly hooked up to the stereo. I'd recorded an LP about 10 days before,and had listened to and edited the results on my PC, and to the editing played directly from the PC through to the stereo. I'd left in place the cables the went from the analogue out of my PC to the line in on my preamp.
Disconnected the pair of analogue cables...and the problem stopped.
I still don't understand exactly why the PC/pre connection would cause this, but relate the incident here b/c it may help others. Apparently the PC was sending out a signal over the analogue out, even when I wasn't "playing" anything, and even tough that set of "outs" wasn't chosen as the default output.
Computers are noise/interference generators, and you definitely want noise and electrical isolation between them and your sound system if you can manage it.