schamberlain@wateng.UUCP (Ray Chau) (11/08/83)
Recent modifications in the RIAA phono section according to "Lipshitz" to the venerable Nad 3020 has cleared up the veiling which "Moncrief" has referred to. The modifications consists of replacing carbon resistors with equivalent metal film components and polystyrene capacitors for the creamic caps. Time constant changes were optimized on a personal computer and verified under listening tests via Ruby/Oracle/Nad/ADS interface. However, it was found that the high level section was a second limiting factor. In order to eliminate this variable, we performed what could be termed a "high level bypass" by taking the phono preamp directly from the tape monitor output (ie. tape out) and patching it directly to the amplifier input. This results in a very reasonable listening level, and the inecapable conclusion that the limiting factor in many good preamps are the high level sections where tone controls, bad caps, and even bad design reside. It should be emphasized that the above interconnection can provide an an answer to the longstanding question of "Am I or am I not Hirsch Head ?". In addition, it will solve the dilemma face by those who are entertaining thoughts as to whether or not it is worth making all those capcitor changes, since the high level bypass is as near perfect a modification as one can make: That is until one dwells in the land of "interconnects" or one designs a piece of wire with that rare quality called gain. There are other standard mods performed, but this message wishes to see what interests exists in "modland". Interested parties might send mail to me personallly, and if the influx is sufficient; a follow up article will be posted. Finally, a premature mod involving circuit changes and d.c. biasing changes seems promising but I'll wait until it's been simulated on analysis package, WATAND. Raymond Chau University of Waterloo Department of Electrical Engineering Waterloo, Ontario Canada N2L-3G1 . . . s