Pre II cathode follower query

[buddam]

Hi all

I sold my Pre, PSU, Phono II 18 months ago and bought it back later. It has an electrolytic cap (100uF) and resistor per channel that I don't recall being there when I built it. Sometimes (aargh!) after a hour or so's use it gives out a very loud rustling noise on the Left channel, which I suspect is caused by the electrolytic (I have changed the valve, with no effect). Can these, and the resistors (see photo) simply be removed? What would have been their purpose?

EDIT - just found this and guess it relates to the caps/res: "The Pre 2 had been converted to a cathode follower already, which overcomes the original design’s hum issues. So this time I increased the size of the power supply choke and converted the power supply to a pseudo mono set up."

The choke can stay, but what is pseudo mono? Is this the cap+res change or does it mean changes have been made to the PSU?

I hope these Qs can be answered without seeing the units. Thanks for any help.

Adrian

[Phil Y]

Looks like separate R-C filtering has been added to each channel, as far as can be seen at least. Could potentially improve sound. Can you see the value of the (large green) resistors?

Phil.

[buddam]

Hi Phil

thanks. The Rs are 150ohms. 7W rating

Adrian

[Phil Y]

Hi Adrian,

I would have thought that it would be perfectly safe to take the cap out of circuit but leave the resistor on the offending channel. See if that seems to cure the problem. Then you know if the cap is to blame. It could also be a coupling cap but if they are plastic film type type, unlikely. It could even be a resistor, they can "rustle" when starting to fail.

Phil.

[bob orbell]

It could be there is a bad connection, without meaning any offence, it dose look quite poorly constructed. BOB

[buddam]

Thanks chaps. It is actually beautifully constructed but poorly photographed in poor light!!

Sod's law - I played it for 2 hours yesterday with no problem at all. When the noise comes, by the way, it is more than a rustle - it is louder than the music. I don't know if this affects the diagnosis. I also noticed quite loud, and prolonged, cap discharge after I switched the pre off a few days earlier. Again, this might help the diagnosis.

Can caps heal themselves? ie can the problem disappear?

Best

Adriana

[Phil Y]

Hi Adriana,

Not sure what you mean by "cap discharge noise" but if the noise is louder than the music then I really don't think that it is a failing capacitor. That will typically give a sound like someone rustling a piece of paper in front of the speaker. If the noise is that loud it really does point to a bad connection somewhere.
It could be anywhere, PSU or signal, don't assume anything, although signal would seem more likely. Start with the basics i.e. are all cables plugged in firmly? (Not just to the pre)Wiggle plugs to see if connections are good. Are you using any cables that could be suspect? Once that is ruled out then start carefully checking wiring inside the amp on the dodgy channel and see if you can spot anything.

Phil.

[buddam]

Thanks Phil, that's helpful, although I have always been pretty careful about connectors etc. But the fact that it has stopped may suggest exactly what you refer to

[pre65]

I had a similar problem on my Pre3.

Took me ages to find out it was a coupling capacitor.

The offending one was a Clarity Cap.

[buddam]

Twas indeed a loose inter-connect. Playing beautifully all week7