Here we've got a nice Kenwood C2 pre-amplifier. The unit came in for an overall recap and OPAMP upgrade. Leestereo of Audiokarma was very helpful with additional OPAMP information from his Kenwood C1 rebuild, big thanks to him and his work, truly top notch.
Each stage has its own power supply, where as the electrolytic were replaced with high temp long Panasonic FR/FC capacitors, I prefer this application vs a audio grade. In a power supply were looking for an extremely reliable capacitor, the Panasonic FR/FC series deliveries just that.
Note that the phono/tone/flat amp stages feed a 18.6-18.5Vdc rail to each OPAMP quadrant. the rated parameters of the NJM4580 and NJM2068 OPAMPs are 2-18Vdc. For continued longevity of the OPAMPS D13/14/11/12 should be replaced with a 16-17Vdc zener to drop that operating 18.5-6vdc rail voltage.
The following OPAMPS were upgraded along with new gold contact 8 pin DIP sockets for future rolling;
Phono - NJM2068DD
EQ stage - NJM4580DD
Tone Control - NJM4580DD
Filter stage - NJM4580DD
For all other electrolytic Elna Silmic or Bi-Polar MUSE ES were utilized, all low value lyrics were replaced with a polypropylene ECW Panasonic film capacitor.
I have to say, pairing this C2 with a Nikko 440 Alpha amplifier is quite impressive. There was a notable difference between the the original 2041DD JRC OPAMP and the NJM2068DD OPAMP. Impressed….