How a phono stage works

A turntable’s cartridge makes a tiny signal, a few thousandths of a volt, hundreds of times weaker than what a CD player or a streamer sends out. A phono stage sits between the turntable and the amplifier and brings that signal up to line level, so it can go into any ordinary input. Many integrated amplifiers have one built in, on the input marked Phono, and this box is the same circuit on its own.

Records are cut with the bass turned down, so the groove doesn’t swing too wide, and the treble turned up, so it stands clear of the surface noise. That recipe is the RIAA curve. Inside, the first stage adds gain, and a network of resistors and capacitors turns the bass back up and the treble back down by the same amount. A moving-magnet cartridge needs about 40 dB of gain. A moving-coil cartridge puts out less again, so it needs about 60 dB and a different load, and the MM/MC switch and the small loading switches by the inputs set both.