The AB528 is a transformers coupled, class A mic preamp. The design, from the late 60's, is inspired by a legendary console, that was used at the most famous London studio by the greatest artists, such as the Beatles or Pink Floyd.
The MP 5.12 is based on one discrete Op-Amp, one Cinemag input transformer and one Cinemag output transformer.
The MP566 is a dual-triode vacuum tube circuit preamplifier based on a design that has been used in several famous devices from the 50's, which has been adapted to the '500' format of API*.
The MP573 is a two stages, single ended class A preamp, based on the design that was originally used in the Neve 1290/1073 modules, that has been adapted to the '500' format of API.
The MP 599 is based on one SK99 discrete Op-Amp, one Lundahl input transformer and one Lundahl output transformer.