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In Reply to: RE: Can a Conrad Johnson PV14L be upgraded? posted by RhythmDevil on February 14, 2015 at 07:15:25
You can do many thins to upgrade the CJ without losing that CJ midrange. Caps are one thing, but a lot depends on your ability to solder and modify
Follow Ups:
Cool. Tell me more, or point me in the right direction.
I'm a EE, and have some soldering skills. :)
Cerebrate!
can never tell on the internet....
Simple mod:
1. add two Mad Scientist Audio Kegs on the B+ power transformer leads ( one keg per lead). Easy and cheap ( $30 per keg). Significantly adds to the detail by lowering the noise floor.
2. The PV-14 , IIRC, uses an MJE340 as an output buffer. Each of the two MJE's are fed by the M8080 (6GK5). B+ for the MJE 340 is fed by the series pass regulator also fed by an MJE 340 ,IIRC.
decouple each channel with a FR diode. That is cut the PCB trace and bridge the cut with a diode. This reduces the cross talk between each channel. Sonic increase is greater dynamics, and detail. I use a small cap on the 340 side of the diode (5 to 10 uF 400V cap). electrolytics work fine.
3. You can do the same for the B+ pf the M808o's too.
You can do this yourself and just as Stu said,caps are where you can start..To tell the truth,CJ has a nice film cap power supply which is what I do when I rebuild all my vintage amps and preamps for myself and others.
About all you want to change in that PV14 is change some output and interstage coupling caps to Russian paper in oil or a good film and foil or both..You could then put some Schottky diodes in the power supply and resolder the connections on the tube sockets if needed..THat preamp is super the way it is.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
So true -Stu.
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