This is the RIAA correction module for the PhonoDude. The most important part of the phono amplifier. We have matched the capacitors and resistors out of hundreds to get a RIAA correction within 0.1% on both channels. For DIY PhonoDude builders we offer this RIAA module separate. It is exactly the same we use in our PhonoDude kit. It is highly recommended. A matched RIAA curve will dramatically improve the quality of the PhonoDude.