Humming and static noise, Plinius SA 100 MkIII

Thank you for your input. I'll try some of the suggestions including using one amp as stereo and post the results. Thanks again.

Thank you all for excellent advice although some of it just went over my head. I did one more experiment and changed amp on one side. A VAC tubed amp. The hissing noise was still there at high volumes without any input from source. So somewher, I am picking up the noise where than is amplified by the amps.

BTW, I am using a Richard Grey Power Station and RCA connectors since my preamps don't have XLR connection.

I tried everything I could and it appears the noise is from amp or some signal it picks up. The noise is there even when the CD player and the preamp are off. I also tried stereo mode rather than mono with no luck. I even tried without biwiering and still the noise is there. Now even at listening volume levels the hiss is there and getting more anoying by the minute. Thanks

OK. It appears the amps have some noise (barely audible). The preamp, when turned on, picks up the noise and amplifies it even with the volume at zero. The higher the volume the higher the hissing noise. CD player has no effect on the noise. Thanks

Update: I did everything evrybody suggested and still have the noise even with some tubed amps with volume control which don't need a preamp. I changed power cords and interconnects as well with no luck. Also disconnected the cable TV, etc. The tubed amps have only 18 watts per channel so the noise is less audible but not as much as 400 watt per channel Plinius. Any other suggestions. Thanks

I appreciate everyone's input. I could accept the noise is from the amps and move on, but I have tried 2 different brand amps and they all produce the same noise at different levels, so something in my system such as power source, is introducing the distortion and the amps amplify the noise. The only thing I haven't been able to try is to use the XLR connections. But my current preamp does not have balanced outputs and I don't want to invest in a new preamp, cables, etc and still have the noise. I have a home theater room with dedicated 20 amp circuit. I'll move the Plinius to that room to see if it makes a difference. After that, I have to decide to keep the amps and live with the distortion or sell and buy something like Pass Labs or Classe. The reason I originally purchased the Plinius was because it is the only amp that I know of which has a clas A and A/B selector.

BTW, when I was using my other amps to test the noise level even my wife noticed the very poor sound quality compared to the Plinius. So the chalenge continues. Thanks

I am using unbalanced S.E. RCA. My preamp does not support XLR outputs. I don't want to buy a new preamp, cables, etc and still have the same problem. unless someone has done this and got rid of the distortion. Again, I am not concerned with the hum as it is not always there. My concern is the very noticable distortion at the speakers, which may be caused by other factors and not necessarily the amp. Thanks

Update 11/24/2010:

Gande is correct, thank you. When I removed the I.C.'s there were no noise. So I replaced them with a pair of very good pure gold interconnects and the noise was considrably less. However, at very high volume without a source input there is still very noticable noise but not at listening levels. So I am thinking probably with balanced interconnects the noise may be even less. with my amps, in either class A or A/B the noise level is same. One other thing that I may try is to remove the amps from a hallow covered shelf and put them on the floor with some isolation base.

Thank you all for your input and looking forward to more comments. Happy holidays.