Specs

550b
550b Four Band Switchable Equal-
Features
4 bands of our famous sounding equalization
Each band offers 7 API selected frequency centers
Reciprocal and repeatable filtering
12dB of boost/cut per band
EQ Band 1 and 4 offer shelf/peak switching
“Proportional Q” narrows filter Q at extremes
Traditional API fully discrete circuit design
High headroom +30dB clip level
Re-issue of 1967 API 550 EQ with an extra band
The API 550 EQ played a major part in the history of
music recording in the USA during the 60’s and 70’s.
Originally conceived for use in API’s consoles, this lat-
est 550 “B” version is a continuation of the original 1967
550 through the 550A with one additional filter band and
several new frequencies. Incorporating API’s exclusive
circuitry and proprietary components (such as the leg-
endary API 2520 Op Amp), the 550b artfully blends the
past with the present. So many hit records still depend
on the unique 550 sound, that the 550b will be an in-
valuable tool you will turn to again and again. The API
550b--unlike any other you will ever use.
Many EQ’s today offer a huge assortment of complex features, but the API 550b
provides exactly the right number of controls to the professional engineer. De-
ceptively simple at first glance, the 550b’s four EQ bands are overlapped signifi-
cantly to aid in dual roles as problem solver and sweetening device. Each band
offers 7 switchable filter frequencies spanning 4 to 5 octaves, selected through
experience by a “who’s who” list of the industries most proficient engineers.
Making use of “API Proportional-Q”, a design introduced by API in the 60’s, the
550b intuitively widens the filter bandwidth at minimal settings and narrows it at
higher settings--without the need for additional bandwidth controls. This feature
minimises the “phase-shift” sound found in many equalizers. The reciprocal
nature of the 550b enables the user to “undo” what has been done previously.
The benefits of the API 550b are most obvious to those who work with EQ on a
continuous basis. The 550b’s ability to affect or reverse tonal modifications is
perhaps the most important feature. If major tonal restructuring is required, the
extraordinary headroom made possible with API’s 2520 OpAmp offers predict-
able and gentle “analog” performance under duress. With a surprisingly wide
range of tonal variations, you can do no better than the API 550b.
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