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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.
espoverload
espoverload OP
14 posts
 
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
gande
2 posts
 
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.
espoverload OP
14 posts
 
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.
uspault's avatar
uspault
2 posts
 
those noise pick up from the XLR input.you might want to try use a pin plug in those XLR input ,it should take care the problem .
brooney
2 posts
 
I had a hum/hiss problem with my amps that I struggled to find the problem without success.  It turned out to be a motion detecting exterior light with the switch in my audio room. These lights use RF and the switch is always left on so that motion near the light fixture will turn them on. I turned off the interior switch and the noise went away. Light dimmer switches can have the same effect.
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