Memphis MC 1Discrete Solid State Moving Coil Phono Stage
Almost all MC phono head amplifiers are implemented as voltage controlled voltage sources with an ideally infinite input resistance and resistors across the input to optimize the input impedance for the specific cartridge in use. Operational amplifiers but also discrete low noise jFets suit this purpose well. Specifically operational amplifiers are gifts from heaven for the audio industry. Their „plug and play“ option, the need of few external components, excellent power supply rejection ratio (PSRR) and easy gain adjustment over a wide range make operational amplifiers universal and cost effective devices and obviously they are getting better and better. However, the effects of huge global feedback on the audio signal are still discussed controversially.For discrete designs JFets are considered an easy option for their almost infinite input impedance, easy operation point settings and somehow tube like characteristics and I used them a lot. However, jFets exhibit relatively high gate capacitances, poor linearity and gain compared to BJTs (fig. 1a and b) and their electrical characteristics scatter over a wide range (fig. 2).The new phono stage Memphis MC 1will be a discrete no-feedback concept with BJTs only in the direct signal path. The underlying philosophy is similar to my Il Trovatore phono stage. The project is at an early stage of its development. Nothing has yet been built. Currently I am testing LT spice simulations. Thus this part of my website is more considered my personal laboratory note book which I will expand constantly. For the moment there is onlythe basic concept.