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API Audio 550A
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Few equalizers enjoy the respect and admiration of the coveted API 550A. Designed by the now-legendary Saul Walker in the late '60s, 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 its 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 EQs 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 21 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.

With the long-awaited reissue of this unit, an EQ that has had such a part in the history of recording is continuing to make history in today's music.


Acustica audio acqua plugins general discussion

...reasoned approach to Acustica purchases. Here are my go-tos and ones I recommend for newbies. PINK - Based on the API 550a and 550b equalizers. Along with a modified API 2500 compressor sampling. I can equalize nearly any instrument with PINK and the compressor half works great on the drum buss. SAND - Based on...

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Acustica audio acqua plugins general discussion

...Siemens' response to the UE100/UE1000 mastering equalizers. Pink (12) - • EQs: Based on API 550a (A), 550b (B), 5500 (C), 560 (780/PEQ) and CAPI LC53A (D) but have continuous gain and constant Q (bandwidth) options. • Compressors: API 2500 (strip) and modified 2500 with crossover filters from TubeTech SMC 2B, Masalec MLA-3/4 and a...

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Looking for Acustica Console Preamp Emulations

... • EQs: (A) API 550a, (B) 550b, (C) 5500, (780/PEQ) 560, (D) CAPI LC53A and (E) Sound Workshop Series 30 (made by former API engineers in the late 1970s). Unlike the hardware the equalizers have continuous gain and constant Q (bandwidth) options. Sum and difference (mid-side) matrix now available (PINK 4). ...

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