API 550A SW EQ - Saul Walker Edition (Used)

Few equalizers enjoy the respect and admiration of the coveted API 550A. Designed by the now legendary Saul Walker, an adjunct instructor in music technology, the 550A has been used in recording studios throughout the world, among them the Record Plant and Sunset Sound, and by such musical greats as Jimmy Page, Phil Ramone, the Doobie Brothers, Stevie Wonder, Leon Russell, Frank Zappa, Marvin Gaye, Herbie Hancock, and Bob Dylan. In 2008 the API 550A was inducted into the Technology Hall of Fame at the annual Audio Engineering Society (AES) Convention held in San Francisco.

Walker, a fellow of AES, designed the equalizer in 1968, and 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. 

What accounts for its popularity and longevity?  "The 550A design provides a fast, repeatable, and virtually foolproof mechanism to enhance or accentuate specific segments of the audio spectrum or to de-emphasize other tonalities while maintaining the essential integrity of the program material," Walker says. He notes that though newer technology provides greater flexibility at lower cost, permitting more drastic alteration of the sound spectrum, many artists just prefer the sound of the original 550A.

Users of Walker's equalizer are fond of its acoustic properties – the 'sweet tonal change' coursing through the mix and its settings that allow for 'more bite or body' in the basses. "An equalizer is, in a way, a musical instrument," Walker says.

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 push-button "in" switch allows the EQ to be silently inserted into the signal path. A small toggle switch is used to engage the band-pass filter.

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. 

This long-awaited, limited edition reissue is a continuation of the equalizers produced by API exactly as they were in the 1960's, featuring hand-wired switches, the original circuit board design and API founder Saul Walker's signature on the chassis. an EQ that has had such a part in the history of recording is continuing to make history in today's music.


Features

• 3 bands of classic API equalization
• Each band offers 5 API selected frequency centers
• Reciprocal and repeatable filtering
• Maximum 12 dB of boost/cut per band
• EQ bands 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