A Phono Stage (aka Phono Preamp) is necessary if you want to play records.
They usually come in two ways:
a Preamp/Receiver will have a built-in one, like our M Series 'phono' pre-amps or,
a External one such as the Audio Note M RIAA presented on this page.
If your Stereo Preamp/Receiver does not have one built-in then you need an external/stand alone Phono Stage to play records. And even if your Preamp does have a built-in one ~ you can still purchase a separate, higher quality once, to increase performance.
The M1 - M8 preamplifiers come as a 'RIAA' only version for those who use integrated amplifiers or have a line only pre-amp. The performance of our RIAA Preamps is already legendary. Being major record collectors, we have always felt the need for a top flight phono-stages, focussed on getting the absolutely best from the LP, whether mono or stereo.
They are really designed to maximise the quality of all LPs made with the RIAA curve, whether mono or stereo.