The EQ573-II is an parametric equalizer based on the design that was originally used in the Neve 1073 and 1084 modules, that has been adapted to the '500' format of API*.

The EQP501 is a passive equalizer based on the classic PULTEC EQP 1A, adapted to the '500' format of API*.

The EQ250 is a 5 bands stereo parametric equalizer inspired by the revered Sontec MEP-250A, adapted to the 500 series format.

The EQ531T is a 3 bands tube equalizer plus High pass filter, built around a dual triode, adapted to the 500 series of API*.