Conrad-Johnson PV10 Pre-Amplifier
Today were show casing a very very nice Pre-Amplifier rebuild and upgrade, the Conrad Johnson PV10 Pre-Amplifier. The PV10 was produced in three version PV10,PV10A and PV10B. The PV10 and 10A differ from output stage compliment, the 10B features again a different tube topology and slight variations to the circuit design.
Many consider the PV10 to be a bit bright with some noted distortion discrepancies due to its extremely high output of 25.5V with the 12AT7 and 5151 original compliment. Improvements were implemented in the 10A including replacing the two outputs to 12AU7 (lower gain) dual triode tubes and some output coupling capacitor changes discussed further below.
BEFORE
AFTER
Power Supply
The PV10 operates off two bridge rectifiers one with a total film 20MFD filter supply and the 1A supply with a series of 4700/22MFD capacitors.
Diode array for the 1A bridge were all replaced with a Ultra-Fast, Soft Recovery Vishay axial diodes with the original .01 bypass capacitors replaced to a 1kV high grade polypropylene ECW Panasonic film capacitors. The 4700MFD capacitor was replaced with a long life CDE type and a low impedance highres temp (105C) Nichicon PW with an increase in operating voltage. The other bridge reservoir capacitor were replaced with large 20MFD high grade MKP Solen polypropylene film capacitors. The remaining 13.4/4MFD films were also replaced with MKP Solen’s. The 340 transistor was replaced with a robust TO-127 Fairchild device with new Wakefield performance thermal compound applied.
BEFORE
AFTER
PV10 —> PV10A Output Conversion
The output stage of the PV10 with the original compliment has lead to some harsh reviews with the substantial gain stage employed later revised to a 12AU7 compliment on the PV10A version.
...Excerpt on Line Stage Signal Phase
The first route was to replace the 20/150PF to 47pF/1KV ceramics and replace a half dozen of the 1/2W resistors to different value carbon film 1/2W resistors. Also a 1MFD high grade MKP Solen polypropylene film capacitor tied to the B+ and ground for each channel. The coupling capacitors are increased from 2MFD to 4MFD value coupling capacitors which I used again high grade MKP Solen polypropylene films which completes the conversion to a 12AU7 stage for the phase inverting line stage.
BEFORE
AFTER
RIAA EQ
The RIAA stage is a 47K/input MM/MC capable phono stage using a pair of high gain 12AX7 as gain stage multipliers with a passive buffer and a AT7 tube compliment. Unlike the Line stage, the RIAA in the PV10 is not phase inverting.
The film compliment here of the .1MFd and output coupling 2MFD capacitors were both replaced with high grade MKP Solen polypropylene film capacitors.
BEFORE
AFTER
RIAA Curve Response
9 Pin Sockets
The original sockets showed some tendency to separate at the internal pins requiring frequent re-crimping. The old 9 pin PCB mount sockets were all removed and replaced with quality ceramic base/ gold pin sockets for a firm seated placement of each tube. New gold-pin Electro-Harmonix 12AU7 tubes for the line stage output.
Audio Notizen
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