API 550A Discrete Classic 3 Band Parametric Equalizer - 500 Series Classic ModuleFew equalizers enjoy the respect and admiration of the coveted API 550A. Designed by the now legendary Saul Walker in the late 60's, the discrete 550A was first used as a modular OEM equalizer. As the industry rapidly embraced the sonic quality of the 550A, it quickly found it's way into many custom console designs by Frank DeMedio and other leading engineers. Many of these consoles are still in use today. Forty years later, the 550A remains the