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.
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.
API's legendary Saul Walker designed the "timeless" 550A in the late 60s. Originally a modular OEM equalizer, the 550A quickly found it's way into many custom console designs by Frank DeMedio and other leading engineers, many of which are still in use today. This often-copied but never duplicated equalizer became API's standard channel module EQ when they started manufacturing consoles in 1971.
Providing a true replica of the famed API 550A equalizer was no small undertaking for API. Jeffrey Bork, head API engineer, comments: "We've gone to great lengths to ensure that the new 550As are exactly (and I mean exactly) the same as the original. For starters, API constructed exact duplicates of the metal work and circuit boards from the original artwork. We made silk screens from the same original artwork for the new front panels. The 550A uses the same output transformer that API has used throughtout the years. And to keep everything exactly the same, we went to the original manufacturer for the exact same rotary switches and the same Schadow switches for the bypass. What you end up with is an exact replica even down to the gauge of the wiring and the harnessing- even the original documentation is included. Everything is so exact that people with older 550A EQs will now be able to buy matching units or purchase parts to refurbish and fix their older units."
"It's basically the next production run of API units from the early eighties. And its worth mentioning that we never even considered trying to make the 550A 'better,'" added Bork. "There just wasn't any need to do that. The industry holds the 550A in pretty high regard and wanted it "the same as it ever was." It's been an honor, and a tremendous amount of fun, leading up this project."
The 550A uses bridge-T filters (RC networks), two of API's 2520 discrete amplifier modules, a 1:3 output transformer, and provides up to +28 dBm output level. All three of the frequency bands overlap and there is up to +/- 12 dB of boost or cut in 2 dB steps available for each band. There are choices of shelving and peaking for the Hi and Lo band and a switchable, 12 dB/octave, 50 Hz to 15 kHz bandpass filter.
A very desirable feature and so important to the classic sound is the proportional Q design where the bandwidth (or Q) of the equalizer narrows as boost or cut is increased. The Q is three octaves wide at 2 dB of boost/cut and narrows down to one octave with 12 dB of boost/cut.
API - 550A
