Humming and static noise, Plinius SA 100 MkIII

Hello. I am currently using a pair of Plinius SA 100 MkIII's as mono blocks to power my B&W 802D's. First the amps have a slight hum when on and sometimes they are very quiet. More importantly, when I turn the volume up all the way without a signal from source, there is a very noticable high frequency hiss like radio signal distortation at the speakers. I have tried many things including changing preamps, cables, cords, etc but nothing worked. These amps generate 400 watts as mono so with the volume turned up all the way the noise may not be abnormal.

I would appreciate if any one with similar issue has an answer for me. I love the amps but the noise level is a bit too high. Note: in normal listening volume the noise is very low and not noticable at all only at vey high levels the noise is very noticable. Thank you.
I'm not sure the source of the hiss you hear is actually from your amp.

Consider that when turned on an amp is at full power all of the time. It's noise floor, to the extent it is evident, will be constant. It will not be affected by the position of the volume control if your preamp is off. What you hear with the pre-amp off probably represents the noise floor of your amp.

When you turn your preamp on it is also at full power as seen by your amp, even with the volume control minimized. The amplifying stage of a pre-amp is NOT affected by the volume control which preceeds it in the signal path. If you hear a hiss now, that wasn't there before, you are hearing the noise floor of the preamp.

If you have no noise until you turn on (and select) a source and you then note that the noise increases with rotation of the volume control, you are hearing the noise floor of the source (or the recording playing on the source). All your volume control affects is the level of the gain from the source before that signal reaches the amplification section of the preamp. It does not actually control the preamp's output gain which is constant.

That might explain why your hiss varies with movements of the volume control and exists even when you are using different preamps.

Something to think about..........
This amp (I have had two of them) does not behave as well in bridged mono as in regular 2-channel stereo. I couldn't use mine in mono at all because of distortion problems.
Try running the amps in stereo, instead, and see what happens.
Thank you for your input. I'll try some of the suggestions including using one amp as stereo and post the results. Thanks again.
Using the same, in bridged mono on 91 dB speakers. And that's along with a Genesis/NHT active x'over/1600W bass amp. Never heard anything more than a slight pop, very rarely. I've had a stethoscope on them. I'm also using a 5KVA transformer coming off 240V stepped down to balanced 120V just for the SA100's. Balanced AC doesn't really bring anything to the Plinius amps as I've tried it as a isolation transformer as well with no discernible difference, and that does have the advantage of not derating the transformer by half. Has generally been more beneficial for sources and preamps than amplifiers.

Strictly using an isolation transformer will eliminate DC offset but that may also just mean relocating the noise from the amps to the iso. There are cheaper ways to eliminate DC, like PS Audio Humbusters but transformers have other advantages. Some have used Topaz/Xentech iso's near the breaker panel along with/without dedicated lines. The Plinius draws 500W each but an iso transformer should be at least double that capacity.

The Plinius is very high gain (38 dB, where "normal" is 25 to 29) in bridged mode with XLR cables, which accounts for the noise at a high volume setting. I'm using a passive TVC "preamp". Not only is no preamp gain required, the TVC provides galvanic isolation.

For myself, the difference between stereo and bridged mono was in the nuance. It's possible, with lower impedance/more reactive speaker loads or mismatched components, bridged mode might not be the best choice. In my case, the speakers are a fairly benign, mostly resistive load but only 4 ohms, which a bridged amp "sees" more like 2 ohms. Do your own research on that.

Before the MkIII, Plinius had a reputation for mechanical hum from the large internal transformer, particularly after one magazine review. The MkIII addressed this by using 2 smaller transformers. It's something that can affect any amp but bigger amps more so.

All the above is assuming you've already gone through all the ground loop/ cable organizing/ dimmer switch/ etc. protocols. Also assuming that you're using XLR cables and taking advantage of differential operation.

The way I did it... cheaply.
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.
OK. I'm going to assume that my comments were the confusing ones. Here is a simple method for locating your noise.

1) Turn on your amps only, but have them connected to the pre-amp. Any noise?

2) Assuming no, now turn on your pre-amp with volume minimized. Any noise now?

3) Assuming no, now with the source (like a CDP) turned on, but with Volume control minimized is there any noise now?

4)Assuming no, now with source turned on but not playing anything increase your volume control. You hear the noise now?

If the answer doesn't become obvious to you then, feed back with results and I'll tell you what I think might be involved.
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
Suckered again.

Disconnect cable from TV. Any noise?
Turn off all dimmer switches ...
Try without RGPS ...
I agree with Ngjockey, I think your source of noise is external to your components. Sounds like your PC's/IC's are picking up some RFI.
Plinius amps are noted for hum/noise problems. I had a friend that had these feeding Arial speakers. The hum was awful. He was told by Plinius that they are investigating a fix.
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
Maybe it is time to think about your source of electricity. What other things do you have on the same line? I have both dedicated lines as well as regular outlets in my audio room. While I do not have an RFI problem such as yours, the dedicated lines are definitely quieter than than the regular outlets. FWIW.
Plinius amps do have a very high background noise. All of them! I had my combo sent back, they lowered the gain. They also told me, if they lower gain at power amps(rca 32/ xlr 38), the sound they strive for, is not possible. No preamp can change this.
I used SA-102 and SA-250mk4. They sound very good, but this is either something you have to live with, or sell and buy another brand. Oh, the transformers hum, is also typical but not constant.
I noticed all suggestions, i am sincerely honest. This is not a problem outside the amp, it is the amp. I had so much argumenst with mty amps, the store even bought one back. It is accoring to email respons with Plinius, same with new amps. They told me, if i could not accept the SA-120 and 250mk4, i would not accept SA-103 and Ref amp. I bought krell after. But i have moved on. Krell is not not close in signum. maybe you should listen to older Classe gear or Macintosh. Your call!
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
Are you using balanced or RCA inputs?
Hi with my mk3,rca gives a hum and a small power surge,when i turn on the pre.Balanced it dissapears.I couldnt sell my 250.
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
I have a SA50 and a SA102 and they both have the same buzzing sound when running in class A. they are dead quiet when running in class A/B though. The amps don't buzz when nothing is connected to the input or when the mute switch is activated, there is also less buzzing when a tube pre is connected.
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.
those noise pick up from the XLR might want to try use a pin plug in those XLR input ,it should take care the problem .