Replace 25 Year Old Metalized Polycarbonate Film Cap?

[PreCD]

Originally Posted by AndrewT

listen to and measure the his when the input of the amplifier is shorted.
Now subtitute an 1k0 for that short and listen and measure hiss again.

Now go though your various sources connecting one at a time and one channel at a time and listen and measure the hiss.

Are any of your source noisier than the 1k0 resistor?

Andrew:

Thank you for the trouble shooting procedures. Headed out to breakfast but will complete this when I get back in.....

[PreCD]

Andrew:

Ok. The family has not yet arisen for breakfast so I had the chance to short the input leads of the power amp. Quite as a mouse. Quieter even. I am poking around for the 1k resistor.

[AndrewT]

It should be just as quiet (measured).
When you exceed ~10k then you will measure and may hear more noise.
By the time you get to 100k you should clearly hear more noise.

But, I am suggesting 1k0 as a starter just to check that the power amp stays quiet when connected to a typical Rs.

[davidsrsb]

So long as the old Wima capacitors are not damaged and out of spec, they will not be causing the hiss. The best way to spoil "box" capacitors is to fit the wrong size for the pcb and bend the leads too close the case, cracking the seals

[PreCD]

Originally Posted by davidsrsb

So long as the old Wima capacitors are not damaged and out of spec, they will not be causing the hiss. The best way to spoil "box" capacitors is to fit the wrong size for the pcb and bend the leads too close the case, cracking the seals

Thanks for the input. Yes I agree about trying to bend the leads on the box caps.

Still trying to find the time to experiment with the input leads as Andrew suggested.

[PreCD]

Andrew:

It has been awhile since we spoke about this issue and you were very kind to give me advice about using shorting plugs. I found the time to craft a pair, plugged into the inputs of my power amp, and all was quiet using a 1K resistor.

I did as you suggested and started down the line of my Adcom GFP-565 preamp inputs with the shorter plugs. None of the inputs I shorted made a difference in the hiss. As far as I could tell the level of hiss stayed consistent with the ear, not measured.

Again the hiss is not audible from a distance of a foot, maybe two if the house is dead quiet. That will give you an idea of the amount I am hearing.

Originally Posted by AndrewT

It should be just as quiet (measured).
When you exceed ~10k then you will measure and may hear more noise.
By the time you get to 100k you should clearly hear more noise.

But, I am suggesting 1k0 as a starter just to check that the power amp stays quiet when connected to a typical Rs.

[AndrewT]

That leads me to make two tentative conclusions.
1.) the system gain may be too high for the music Source you have.
2.) the pre-amp is a bit too noisy for the following equipment.

[PreCD]

I will make this last comment and leave this alone since I posted it in the parts section. I believe the preamp is just a bit noisy. I have it connected to an Adcom amplifier and these should pair well together.

Thanks Andrew for the shorter plug lesson. Slowly but surely my knowledge is building thanks to people like you.

Originally Posted by AndrewT

That leads me to make two tentative conclusions.
1.) the system gain may be too high for the music Source you have.
2.) the pre-amp is a bit too noisy for the following equipment.