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API 550B

Discrete four-band EQ

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API Audio
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Product Description
Additional Information
  • Product Description

    The API 550 discrete four-band EQ played a major part in the history of music recording in the USA during the 60s and 70s.  Originally conceived for use in API's consoles, this latest 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 legendary 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 invaluable tool you will turn to again and again.  The API 550B—unlike any other you will ever use.

    Many EQs today offer a huge assortment of complex features, but the API 550B provides exactly the right number of controls to the professional engineer.  Deceptively simple at first glance, the 550B's four EQ bands are overlapped significantly to aid in dual roles as problem solver and sweetening device.  Each band offers seven switchable filter frequencies spanning four to five octaves, selected through experience by a "who's who" list of the industry's most proficient engineers.  This re-issue design has been taken from the original blueprints and spec control drawings from the API archives.

    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 minimizes 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 op-amp offers predictable and gentle "analog" performance under duress.  With a surprisingly wide range of tonal variations, you can do no better than the API 550B.


    • Four bands of famous-sounding equalization
    • Each band offers seven API-selected frequency centers
    • Reciprocal and repeatable filtering
    • 12 dB of boost/cut per band
    • EQ bands 1 and 4 offer shelf/peak switching
    • "Proportional Q" narrows filter Q at extremes
    • Traditional API fully discrete circuit design
    • High headroom: +30 dB clip level
    • Re-issue of 1967 API 550 EQ with an extra band


  • Additional Information

    Condition New
    Channels Single-Channel
    Chassis 500 Series
    Module Slot Count 1 Slot
    Digital I/O No
    EQ Type Parametric
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