ABSTRACT

Discrete moving-magnet (MM) input amplifiers were almost universal until the early 1970s. When the first bipolar transistor MM inputs were designed, and adding another transistor to a circuit was not something to be done lightly. A major problem with early discrete MM amplifiers was a simple lack of open-loop gain to give an accurate RIAA response network in the low frequency region, even if the RIAA network was accurate, which it rarely was. The idea of loading the MM cartridge inductance with a low input resistance to achieve LF boost section of the RIAA equalisation has come back to haunt us many times since then. The configuration of two-transistor MM input amplifier is generally considered to have been introduced by Jack Dinsdale in 1965, in a classic preamplifier design that was one of the first to deal effectively with the new RIAA equalisation requirements for microgroove records.