500-series format

Originally invented by Automated Processes, Inc. co-founder Saul Walker, today numerous companies manufacture 500-series format products.

[2] In the mid-1970s, some recording engineers began removing individual processor modules from API mixing consoles and installing them into homemade mounting systems.

In response to increasing demand, Wolff introduced the API Lunchbox, a portable chassis for housing 500-series modules in 2-slot, 6-slot, and 10-slot configurations.

[1] Popularity in the 500-series format surged in the mid-2000s, and by 2020, there were over five hundred different 500-series modules on the market from API and numerous third-party manufacturers, including Neve, Solid State Logic, Aphex, dbx, and others.

The physical dimensions are 3U vertically (5.25") and multiples of 1.5" wide, with 15-pin edge-connector pin configuration of 500-series modules.