A phono preamplifier generally consists of three subsystems – Input Stage, RIAA Stage, Output Stage. The input stage, responsible for the main amplification of the delicate signal sourcing from the phono cartridge. This task is extremely difficult. The signal level is only a few microvolts rms, comparable to the noise level picked up in the majority of interconnect cables, along with thermal noise of some active devices.
The input stage must amplify the signal to the last micro detail coming from the vinyl groove, whilst rejecting noise coming from external sources, cables and the turntable electro mechanical system. The selection of the active device used for the input stage is as critical as the design of the topology used.