Not a ground loop hum???

If you have a video cable line or satelite cable, disconnect it, see if the hum goes away. I went through a similar situation a year or so ago. I tried cheater plugs, floating grounds, etc, etc. It wound up the ground loop hum was coming from my cable line. Radio Shack sells ground loop isolators if this is the case. I'm using a MIT Iso-LinQ, no more hum.

Regards,
John

Have you ever verified that your equipment and AC outlets are properly oriented in terms of polarity? Some components are HIGHLY sensitive to AC polarity. Having one component that is not oriented properly connected to others that are oriented properly can introduce a hum into the system.

Out of curiosity, how loud is the hum and at what distance from the speakers is it audible? Is the hum a constant level or does it vary with the gain of the preamp? Have you ever tried connecting the amp to the speakers by itself to see if it hums? If not, try that and see what happens. If no hum, hook up the preamp to the amp and then give that a shot. If nothing, then hook up the CD to the pre and see what happens. If you get a hum with all three hooked up, then try the CD directly into the amp ( NO discs in the unit unless you can vary the output of the CD player ). As usual, it is all just a matter of step by step diagnostics and trouble-shooting. Sean
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All good suggestions above...

I had an interconnect hum once because the solder on a RCA plug was cracked, probably from being moved around too much over the years...

Resoldering did the trick...

You really need to start by unplugging everything in that circuit, not just in that outlet. Then, plug in only 1 piece at a time to find the hum.
Keep in mind that electricians can do weird things (1 outlet in my basement is tied into a kitchen outlet).

Thanks very much for the responses!!!

The IC's in the system: the pair from cdp to pre and the pair from the pre to amp are both essentially outside the equipment rack and neither of them comes very close to a component's chassis. The IC from tuner to pre rests mostly on the top shelf of my rack. I've tried to ensure that IC's are spaced apart from one another and from the PC's.

The system in question is strictly audio, but I'll look into the ground loop isolator idea if all else fails.

Sean, I was hoping you might comment/advise. I checked the outlet into which the power conditioner is plugged with a 3-prong outlet-checker (I've forgottent the proper name) to ensure its wired properly and it indicates the outlet is OK. As for the outlets on the power conditioner, I did not check those but will do so this evening. Although the cheater plugs I found/purchased don't have the ground blade, they are not reversible as one of the two blades is wider.

I don't have a metre to measure the volume of the hum (I would guess that it's about as loud as a really big bumble bee; can't think of another comparison right now), but it is at a constant level regardless of the position of the attenuator. I can hear it from up to 12 feet away, and when I listen at low volume at night (so as not to disturb my better-half or the littl'uns) I can hear the hum between tracks and during soft passages. My pre has the Shallco stepped attenuator and by low volume I mean it's at the third to fifth step.

I had tried several weeks ago hunting down the source of the hum in the sequence that you suggest, but will have to check again as I can't remember the results.

Sugarbrie, if memory serves, the van den Hul's are not soldered, probably because of the carbon fibre layer, and they are barely a year old. But I'll check this as well. I'd hate to think that one of the BC components could be to blame, but the hum is drivin' me nuts.

On a separate noise issue, my MR1200 makes quite a bit of noise that comes and goes. I wrote to Blue Circle and they suggested the AC to my house may be particularly dirty, so the noise is indicative of the transformer/filtering working hard. I don't know, I mean why pay for conditioning/filtering to keep noise out of the audio components only to have it show up in the conditioner/filter. BC also indicated that it may be due to the on/off cycling of the furnace at this time of year, but the two don't seem to coincide. They'll retrofit the MR1200 or the BC62 PC with a quiet device, but I'm waiting until we move to our new place in a couple of weeks before spending anymore on power conditioning/filtering.