Just wanted to report back, the cart sounds excellent and i am able to use the 640p. It has been modded with all new caps and op amps. I do have a gain issue though, have to run my buffer at 75-80% for approx 80db. I have ordered some resistors that i can add to the 640p to boost the gain by 6db. That should do the trick but it is quite listenable now.
Thanks for all the input.
