Mercenary Audio - API 550a 500 Series Discrete Three-band EQ

The 550A is the equalizer by which all other API EQs are measured. This is the famous 3-band module that started it all in the early 1970s. The 550A discrete circuit has always been heralded for being open, punchy, and able to go from smooth to aggressive. This current unit features the original 550A circuit design, maintaining the integrity of the circuits and the sound, while replacing the hand wired, resistor pack switches used in the re-issue version with the 6 pole boost/cut switch API has used for many years in the 550b and the 7600.

api 550a features

Few 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 standard against which other EQ's are measured, and it has played a major role in the recording industry for decades. Still copied but never duplicated, the 550A became API's standard channel module EQ when the company began manufacturing consoles in 1971. With virtually all existing units spoken for, popular demand for this EQ resulted in API finally resuming production in 2004.

The 550A provides reciprocal equalization at 15 points in 5 steps of boost to a maximum of 12dB of gain at each point. The fifteen equalization points are divided into three overlapping ranges. The high and low frequency ranges are individually selectable as either peaking or shelving, and a band-pass filter may be inserted independently of all other selected equalization settings. Frequency ranges and boost/cut are selected by three dual-concentric switches, and a pushbutton "in" switch allows the EQ to be silently introduced to the signal path. A small toggle switch is used to insert the band-pass filter into the 550A.

The combination of Walker's incomparable 2520 op amp, and his "Proportional Q" circuitry gives the 550A user an uncomplicated way to generate acoustically superior equalization.

Three bands of classic API equalization, each offers five API selected frequency centers
Reciprocal and repeatable filtering
maximum 12 dB of boost/cut per band
EQ Band 1 and 3 offer shelf/peak switching
"Proportional Q" narrows filter Q at extremes
Traditional API fully discrete circuit design
High headroom +30 dB clip level

RACK FRAME AND POWER SUPPLY OPTIONS

500B6 Lunchbox - Six position "lunchbox" with internal power supply
500V - Ten position, rackmountable frame with external power supply
API Legacy Consoles and vintage API Consoles.

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