“Hand-Wired, Simple Design Minimizes Phase Shift”

YEAR: Late 1960s

HISTORY: The API 550 EQ was designed by Saul Walker in the late 1960s and was first used in API and custom console designs. It has been a very influential piece of recording gear and has been used on countless hit records. It is a 500 series module, which means it needs a 500 series enclosure or “lunchbox,” or needs to be installed in a console that uses 500 series modules. It has a unique sound due to the custom Saul Walker-designed 2520 op amps and the “Proportional-Q” circuitry, which automatically adjusts the bandwidth based on the amount of EQ applied.  This innovative feature eliminated the need for a bandwidth adjustment and also minimized phase shift. Phase coherence is especially important in recording very tight, low end in instruments such as bass guitars and kick drums and this is where the 550 shines. Many recording engineers swear by the vintage 550s due to the hand-wired, simple design and more direct signal path.  Continue reading →