RIAA Equalization of a phono cartridge’s signal (boost bass/cut highs) must occur somewhere, and a phono cartridge’s signal strength must also get boosted UP to Line Level strength, then thru a volume control then to the amp.
Unless specifically noted as MC, built-in Phono Stages provide RIAA EQ. They only accept ’sufficiently strong’ Phono signals of two types:
1. MM Moving Magnet typical signal strength
2. HIGH OUTPUT MC Moving Coil, signal strong enough that it does NOT need any pre-preamplification.
IF you ever get a LOW OUTPUT Moving Coil Cartridge, those signals need pre-preamplification, to get up to the strength of MM or High Output MC. After that, RIAA Equalization and normal preamplification up to Line Level must occur.
Step-Up-Transformers (SUT) are made to increase the strength of LOW OUTPUT Moving Coil up to the strength of MM or MC High Output. That pre-preamplified signal then needs to go thru the RIAA Equalizarion process (somewhere). The SUT can be a separate device, OR, it can be incorporated in a Preamp, always labeled Phono MC. Either a separate Phono MC input jack, or a single jack that can be ’switched’ to either MM or MC. The switch can be in the front or back of a unit.
Note: some preamps or receivers have a ’Phono/Aux’ input. They are not true MM Phono inputs providing the needed RIAA Equalization. They are simply NAMED Phono for convenience, they require external prior Phono processing elsewhere.