|Steps to Upgrading the CA 640P (for MC use only)
1. Remove Surplus MM stage and Sub Sonic filter (Don't like filters).
Take out all MM stage components, including the RCA inputs.
Take out the MM/MC change over switch and the SS Filter switch.
Bridge the board switch locations to "MC" and "No filter" positions.
Remove the large SS filter caps - not used and can be seen as an output by op amps in output stage.
Remove the anti thump start up relay. (Another switch with mating contacts to degrade signal.)
2. Replace Op-Amps & bypass Caps.
Fit AD 823 op-amp with 33pf Polystyrene bypass Caps to MC input stage.
Fit pair of LM 4562 op-amps with 22pf Silver Mica bypass caps to dual mono output stages.
3. Replace Power Supply Diodes and Caps.
Fit Schottky 11DQ10 Diodes and Panasonic Caps. Replace wall wart with better unit.
4. Replace main electrolytics.
Fit Panasonic electrolytic caps.
5. Adjust input load to match cartridge. Increase Gain by 3dB.
By several user accounts the Denon DL-301 mkII performs best with 4/800 ohm loading. This is of course, system dependant. I will start with stock 100 ohm loading, but arrange for easy swap out of parallel loading resistors. R54 & R71 (18 ohm) reduced to12 ohm with a matched pair of resistors to give +3dB Gain.
6. Fit panel mounted RCA sockets and test the unit.