Belles amp hum ... rf problem?

Thanks for the tip Rhyno. I definitely would not have thought to try that. Hopefully I can get this figured out quickly!

Tooter

Belles mounts his transformers very well and they are isolated. Unless the transformer is physically defective, I doubt that is where the problem is. It's something coming in on the line. Otherwise, it would hum all the time.
Good question about whether they all would do this. Most amps I've used in the past had an E-core.

I don't have a solution, but I do have a similar problem with the new Belles 150A Reference. The problem did not manifest itself until I attempted a speaker cable upgrade from the shielded LAT SS-800 to the unshielded Xindak FS-2 copper/silver foil. Result was a very loud hum, even with everything but the amp unplugged and the inputs from my 21A pre-amp disconnected. Problem is continuous with the unshielded cable, and is loud enough to make listening to music impossible (all with pre-amp completely removed from the sytem). Problem goes away when my old speaker cables are re-installed (yes, I checked multiple times to make sure I installed the new cables correctly). The hum changes pitch when I move the speaker cables around, but never goes away - I'm no EE genius, but to me, it would seem more logical that this is an EMI problem coming from the amp itself than a ground loop problem, since it goes away with switching only the speaker cables. I also tried lifting the ground from the amp PC with nothing else connected to the amp or plugged in to any outlets on that circuit - hum persisted. I also tried plugging the amp directly into the wall (my normal method) or into my Panamax line conditioner, with no change. I do, however, have dimmer switches installed throughout the house, and I'm not in the mood to replace every switch to see if that might help! Other than this recent challenge, I have been thrilled with the 150A Ref/21A combo. Any other ideas?

I had the same problem with the intermittent humming. I plugged my cord into a different outlet on the power strip and it stopped. Weird huh?

Hammer 223, as unappealing as it may seem, I would recommend checking/replacing your dimmer switches in your house. I had 3 dimmer switches in my house and after exhausting all other options I finally took these out and replaced them with regular on/off switches and my hum disappeared!

On another note, did you compare the 21A preamp to the 20A preamp before settling on the 21A? I'm interested in trying a tube preamp for my 150A hotrod but am tight on funds and am wondering how much of difference there is between the two.

Tooter