A phono stage accepts an input from a turntable and does two things:
1. Provides equalization- during recording, for a variety of reasons, the frequency response of the music to be recorded is altered in a precise way. These days, its an accepted standard, called RIAA. The phono stage provides the opposite equalization so that the frequency response is the same as the music before it was recorded.
2. Voltage gain or amplication- Phono cartridges put out between about 0.1 and 5 millivolts. Most tuners, CD players, DVD players and tape recorders put out about 2V. Therefore the typical "line stage" input on a pre-amp, receiver, or integrated amp is built to handle an input of about 2V (called line level). The phono stage has to boost or amplify the very small phono signal to line level.
