API Audio 1608 Recording Console - Manual (Page 17)

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2.6 550A Discrete 3-Band Equalizer
The legendary API 550A Equalizer is installed on channels 1-12 in the standard 1608
configuration.
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.
WARNING – WARNING – WARNING – WARNING – WARNING
The use of NON-VPR Alliance approved 500 series modules in the 1608 is vehemently
discouraged, and may cause operational difficulties with the console. Improper
operation, excessive current draw and poor module fit are all potential issues with
these devices.
For the most recent list of VPR Alliance approved modules, please visit
www.apiaudio.com .
API reserves the right to deny warranty claims when non-VPR Alliance 500 series
modules are used.
Features
 3 bands of classic API equalization
 Each band offers 7 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
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 its way into many
custom console designs of the era. 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 resuming production in 2004.