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WAD Problems For questions and answers re older World Audio Design Projects |
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#1
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Pre II cathode follower query
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 Last edited by buddam; 27th August 2018 at 04:51 PM. Reason: additional info |
#2
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Re: Pre II cathode follower query
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.
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Commission for Dark Skies (CfDS) |
#3
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Re: Pre II cathode follower query
Hi Phil
thanks. The Rs are 150ohms. 7W rating Adrian |
#4
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Re: Pre II cathode follower query
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.
__________________
Commission for Dark Skies (CfDS) |
#5
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Re: Pre II cathode follower query
It could be there is a bad connection, without meaning any offence, it dose look quite poorly constructed. BOB
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#6
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Re: Pre II cathode follower query
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 |