Mercenary Audio - API 550b 500 Series Four-Band Switchable EQ

The legendary 550A three-band EQ made API a household name in the mid 1970s. The discrete proportional Q technology defined the 550 as the most supple and musical EQ built this side of the Atlantic. It was the first EQ to allow shelving at 20K, the "air band" as some called it, providing sparkle and breath to vocal tracks. In about 1985 they introduced the 550B, a four band version of the same famous 550 EQ circuit.

api 550b features

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.

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 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

Four bands equalization, each offers seven 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

SPECIFICATIONS

Number of Bands: Four
Low and High bands are Peak/Shelf switchable.
Low-Mid and Mid-High are peaking type
Filter Frequency Centers:
Low: 30, 40, 50, 100, 200, 300, 400Hz
Low-Mid: 75, 150, 180, 240, 500, 700, 1Khz
Mid-High: 800, 1.5K, 3K, 5K, 8K, 10K, 12.5K
High: 2.5K, 5K, 7K, 10K, 12.5K, 15K, 20K
Filter Boost/Cut: +/- 12dB
Filter Slope: 12dB per Octave
Input Impedance: 18.5K +4 in, 7.5K -2 in
Output Impedance: Less than 75 Ohms
Nominal Levels: -15 to +15dBu
Clipping Level: +30dBu @ +/- 16V
Frequency Response: +0, -.3, 30 to 20kHz
Noise: Actual, unweighted noise, <-98 dBu, 20-20kHz
Distortion: .07% max, @ +18dBu Output
Connectors: 15 position .156 sp edge connector
Size: 1.50 X 5.25 X 6 Deep
Power Consumption: 12/18 Volts/DC,@40 ma.

RACK FRAME AND POWER SUPPLY OPTIONS

500B6 Lunchbox - Six position "lunchbox" with internal power supply
500V - Ten position, rackmountable frame with external power supply
API Legacy Consoles and vintage API Consoles.

MANUALS & PDFs

API 550b Product Info Adobe pdf

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