Recording Kurzweil PC3x with Mbox2 Mini: noise problem (possibly ground loop)

[terhardp]

For the past few days, I've spent too much time searching the Internet for the solution to this problem. From ground loop, power conditioning, hum eliminators, balanced or unbalanced cables, ground lift etc. The trouble is that now I'm even more confused... So here's my story.

My rig consists of home-brewed Core 2 Duo system running original W7 64 and original PT8, Mbox2 Mini, Alesis active monitors, Axiom 49 + plus the instruments. I had noise issuses with Mbox2 Mini from the start, which I've solved to some degree by buying balanced monitor and line cables and better USB cable. However, the high-pitched whine is still present when I crank up the input knobs to the max, though it's not a problem when I keep them at reasonable level.

But the problem I'm having currently is with my brand new Kurzweil PC361. When I arm the track, it gives both hum/buzz and whine, which is picked up by PT, depending on the current gain level. I have it connected to Mbox2 Mini with a pair of balanced audio cables, and the keyboard is powered from the same power strip as the PC (with surge suppresion). I've "solved" the problem to some degree by isolating the ground contacts on the plug (EU standard, I live in Croatia). This removes a good deal of the noise (namely the whine), though I can still hear some low-pitched interference when I turn up the volume controls to the max (I'm guessing from the PC itself and its PSU). But the horrible noise is almost gone (tolerable).

Since this clearly isn't the optimal (and safest) solution, I would very appreciate your insight on this matter. Currently I'm not in a position to invest into HQ power conditioner, but I was thinking about getting some middle-ranged UPS unit (Eaton or Trust), which according to the specs, also have AVR function and EMI shielding. Unfortunately, I don't know anyone right now who has such unit, so I can't test it to see if it would make a big difference. So if someone here has experience with UPS units and AVR's, I would be very grateful if you could share it, before I finally "give in" and just purchase the thing blindly, as I'm really at the end of my nerves.

P.S. I also don't have experience with so-called hum destroyers that are placed on the audio cables. Could something like that help reducing the electrical noise, and is it maybe the better solution to this particular problem?

Many thanks in advance,
Tomislav

[terhardp]

This thread didn't help me very much (so far), but I've found the solution.

I've purchased Behringer Hum Destroyer (HD400) which eliminated both the whine and the buzz I was experiencing with my Kurzweil connected to Mbox. I've hooked up the synth to HD400 using a pair of balanced audio cables and HD400 to Mbox with a pair of unbalanced ones. Since I've always used balanced cables with Mbox (I'm still not sure does it really have balanced inputs, but balanced cables seem to make a difference), I must make two more cables today.

However, the Mbox still generates a lot of static noise when I crank up the inputs. When they're on the max, this noise is so powerfull that it shows in Pro Tools 8 mixer. However, this is not such an issue, as I wouldn't record on such high level anyway.

I'm guessing that this is by-design or the computer interference. I've tried to crank up Mbox inputs to the max with something hooked up (via HD400) and without. The noise is the same. I will still try some power conditioning (maybe with a better UPS).