Although Erno Borbely must have designed a dozen or more phono preamps, he never tires of trying new avenues of circuit design to find that elusive holy grail. In this article he teamed up with Sigurd Ruschkowski to design a preamp that considers the phono cartridge as a current source, offering a very low impedance input to the cartridge. The article gives several options to use the basic amplifier in inverting and non-inverting mode and in single ended or balanced mode. The sensitive input stages all use (of course) JFET devices, with BJTs called in for the output stage and an opamp for the DC servo. The article concludes with sophisticated low noise shunt power supply regulator to power the preamp. PCB will be made available if demand warrants it.
Proteus – a current input moving coil preamp