The API 550A is a highly esteemed equalizer that has earned a special place in the world of audio equipment. Designed by the legendary Saul Walker in the late 1960s, the discrete 550A initially served as a modular OEM equalizer. As the industry recognized the exceptional sound quality of the 550A, it became a favored choice for custom console designs, including those by engineers like Frank DeMedio. Many of these consoles are still actively used today.
After four decades, the API 550A remains the benchmark against which other EQs are measured and has been a significant part of the recording industry for many years. While it has been imitated, it has never been replicated. In 1971, API adopted the 550A as its standard channel module EQ for console manufacturing, and its demand was so high that API resumed production in 2004.
The 550A offers reciprocal equalization with 21 points across 7 boost steps, providing a maximum gain of 12dB at each point. It divides the fifteen equalization points into three overlapping ranges, allowing both high and low frequency ranges to be configured as either peaking or shelving. Additionally, an independent band-pass filter can be inserted alongside other selected equalization settings. You can select frequency ranges and boost/cut levels using dual-concentric switches, and the EQ can be introduced silently to the signal path with a pushbutton "in" switch. A small toggle switch lets you insert the band-pass filter into the 550A.
Combining Walker's exceptional 2520 op-amp with his "Proportional Q" circuitry makes the 550A an easy-to-use tool for achieving superior equalization.
With the much-anticipated reissue of this unit, an EQ that has played a significant role in recording history continues to shape the future of music production.