API 550B - Discrete 4 Band EQ

Modular 4-band Equalizer, 500 Series, With 7 API-selected Frequency Centers, 12dB of Boost/Cut Per Band, and Proportional Q Control

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 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 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. 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 7 switchable filter frequencies spanning 4 to 5 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 blue prints 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.

Features :
4 bands of our famous sounding equalization
Each band offers 7 API selected frequency centers
Reciprocal and repeatable filtering
12 dB 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 +30 dB clip level
Re-issue of 1967 API 550 EQ with an extra band