Hissing and Hum through speakers


Hi everyone,
I have a fair amount of hissing and small hum coming through my speakers...when music is played at mid to high volumes the hissing and distortion is very audible through the tweeters/speakers. I don't think it is distortion (not sure how I can tell) I think it is that noise that exists in the system and it gets exaggerated at higher volumes...

I have a Panamax unit where everything is plugged in and the Panamax and amplifier plug in to the same wall outlet.

The noise goes away when I mute my pre-amp (Meridian 561.) But with the pre-amp on and non-muted and any source selected the noise is present. Even when the source is in pause.

Also, I have unplugged the inputs from the pre to the amp (line level) and the noise is still present. Same for my center channel amp, and I also have a third amp with same results..

Does this indicate that the noise is coming from my AC line? I have done most of the troubleshooting (different cables, plugging and unplugging sources, et cetera) that I know and have not been able to resolve...
yanniz
You might try plugging the whole system into another circuit to see if that changes anything.
I don't think that your results with nothing connected to the amp are meaningful, unless you connect shorting plugs to the inputs (which will probably kill both the hiss and the hum, especially given that you initially reported that the noise went away when you had the preamp connected and muted).

As an experiment, I'd suggest connecting the preamp to the amp, a source component to the preamp, and the ac cords of ALL of these components either to the Panamax (if it can handle the current requirements), or else to the wall without the Panamax. That will eliminate the possibility that some or all of your problem is caused by voltage differentials between the grounds/chassis of the different components.

Not sure what you meant by "there possibly seems to be some level matching issues with the 561 (45 Ohms output impedance) and the amp (23.5K ohms input impedance on the rca inputs.)" Ideally preamp output impedance should be as low as possible, and power amp input impedance as high as possible. Those numbers sound fine, although the amp's input impedance is probably lower than typical, which might result in signal loss if the preamp output impedance were unusually high (which it is not).

Regards,
-- Al
Also, you mentioned that you moved the plasma to another circuit. Did you also try unplugging it? If it is physically close, it's possible that it is radiating high frequency interference into the audio system through the air, regardless of what circuit it is plugged into.

Regards,
-- Al
Thanks for your response...I did unplug the Plasma...it is also located in a different room than my equipment is (about 20' away from on the other side of the wall.)

I will try the experiment with 1 source, preamp and amp only connected.

Thanks again...