THE ORIGIN OF API AUDIO AND THE 500 SERIES FORMAT

Modern 10- Slot API 500-series rack, click to enlarge

In the late 1960s, Automated Processes, Inc. (API), founded by Saul Walker and Lou Lindauer, emerged as a pivotal force in professional audio, driven by a mission to craft high-quality gear for recording studios. API’s early innovations, including modular console designs, laid the groundwork for what would become the iconic 500 series format. This standardized, modular system revolutionized audio processing by offering engineers flexibility, portability, and exceptional sound quality.

Heavy duty API power supply, click to enlarge 

The 500 series format was born from API’s console designs in 1967, when Walker and Lindauer created a 12-channel mixing console for New York’s Apostolic Recording Studio, the city’s first 12-track facility. The console’s modular signal processing units, such as preamps and EQs, allowed engineers to customize their setups. By the mid-1970s, resourceful engineers began extracting these modules from API consoles and housing them in custom racks, a practice that sparked the idea for a portable, standardized chassis.

Six-slot Lunchbox™ by API, click to enlarge 

In 1978, Datatronix, which had licensed API’s rights, introduced a 10-slot 500 series chassis, formalizing the format. However, it was in 1985, under Paul Wolff’s ownership, that API truly defined the 500 series with the introduction of the “Lunchbox,” a compact, portable rack for housing modules. Named for its resemblance to a worker’s lunchbox, it offered 2, 6, or 10 slots, making it easy for engineers to carry their preferred signal chains between studios. The Lunchbox’s success cemented the 500 series as an industry standard.

API’s early modules, like the 512c preamp and 550A EQ, became legendary for their punchy, transparent sound, characterized by the 2520 discrete op-amp and Proportional Q circuitry. These transplanted console components defined what it means to deliver professional performance and it’s still true today. Transformer coupled inputs and outputs remains a popular connection standard in 2025, nothing beats a transformer for electrical isolation. 

API 500 Rack used as a Meter Bridge, click to enlarge

EPILOGUE

The format’s open adoption in the late 1990s, coupled with API’s 2006 VPR Alliance, ensured compatibility across manufacturers, spurring a surge in 500 series modules from brands like Neve, SSL and many others. Today, the 500 series remains a cornerstone of modern recording, blending API’s analog warmth with modular versatility, a testament to Saul Walker’s visionary design.

LINK TO: High on Technology Review of API 500 Series 10 Slot rack

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©May 2025 by Mark King, It's not ok to copy or quote without written permission from the author