PF-1 Fet schematic, phono left popcorn distortion?

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kd1yt
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PF-1 Fet schematic, phono left popcorn distortion?

Post by kd1yt »

Hello all - new member, first post. My dad (now retired) is the original owner of a CJ PF-1 fet preamp. It's provided excellent service for 25+ years. Years ago he and my mom listened to lots of LPs - then didn't very much for a long time, but now want to get back into enjoying their substantial trove of vinyl. Trouble is that (only with phono), the left channel has low gain and what I'd call popcorn distortion - only the high amplitude peaks come through, staccato, and fuzzy. Switching L and R cables from the turntable leaves the distortion in the left channel, which tells me that it's in the phono stage of the preamp (no other inputs to the preamp, except phono, do this). Years ago I dabbled extensively in building and customizing audio and DC electronics, both vac tube and solid state, but job, parenthood, etc mean that both my test equipment and skill level are long dormant. Is there any way to get a schematic for this preamp? Yrs back I wrote CJ asking for a schematic for a different CJ unit and they somewhat haughtily said that they were not disclosed to mere members of the public. These symptoms make me think"degraded coupling capacitor" as a likely suspect but I also recall that CJ made it a selling point that they avoided electrolytic caps, especially in the signal chain. Any known 'notorious suspect' components in the phono stage of the PF-1? Thanks in advance for any help!
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Re: PF-1 Fet schematic, phono left popcorn distortion?

Post by admin »

First, welcome to the site. It's nice to have you with us.

Unfortunately we do not have the PF-1 schematic in out database as of yet. Considering the PF-1 is over 25 years old now you can potentially look into upgrading all the caps, or at least in the phono section if that is where the problem is presenting. I presume you took the cover off to look for any over signs of damage such as bulging caps or burn marks? If not, I would start there.

Let us know what happens, great to hear that older CJ gear is being "brought back to life."
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Main stereo: ART Amplifier and ET7s2. 2nd stereo: PV-14L and MV-55. Previously Owned: PF2 preamp, Evolution 2000 Amp, PV-12AL preamp, D/A-2b Vacuum-Tube Digital Processor.
kd1yt
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Re: PF-1 Fet schematic, phono left popcorn distortion?

Post by kd1yt »

Thanks for the response. I did open the cover and nothing looks abnormal. The unit has been in continuous reliable service since new, and it all still works great except the phono setting/stage. I found a local independent repair technician who receives good reviews, and I am going to take it to him since he's got his test bench all set up (versus mine, which is put away/scattered). I'll try to remember to post back whatever the diagnosis turns out to be. Glad to see that the innards are all discrete components, not ICs, so there should be little if anything for which equivalent parts are not available.
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