API 5500 Dual Equalizer
By Barry Rudolph
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The musical-sounding API 5500 Dual Equalizer embodies more than 40 years of tradition, beginning with the original 550 console equalizer module designed by Automated Processes Inc. founder Saul Walker. An industry first in the 1960's and the same as it ever was, the original 550's proportional Q filter design with reciprocal boost and cut is used.
Proportional Q means the filter's Q increases or sharpens with concomitant increases in boost or cut settings. Proportional Q makes the equalizer subtle at lower boost/cuts for program equalization and more aggressive at higher values--better suited for surgical shaping of individual tracks. Reciprocal means that any boost or cut made with the (repeatable) detented controls during a recording can be precisely 'undone' by an exact opposite setting on playback.
It's through this design and the sound the all-discrete Class AB 2520 amplifier that API products have achieved a nearly sacrosanct if not mythical status amongst audio engineers. It's no wonder that API is not interested in changing the basic circuit design and protects quality and component choices religiously. The 5500 is as close to a pair of the original 550B modules as humanly possible.
DOUBLE YOUR PLEASURE
The new Range control broadens the 5500's utility to include mastering applications by changing the four bands' boost/cut steps from the original 2 dB into either 1dB or 0.5dB steps. These additional ranges are exactly like the 550 variants that were custom-built for mastering rooms: the API 550D with +/-1dB steps and the 550M with +/-0.5dB steps.
The internal hand-built construction is strictly pro with a linear power supply for the +/-16-volt rails, single-thick PC board, and positive-feeling rotary and military-grade pushbutton switches. No integrated circuits are used; gain comes from two hand-built 2520 operational amplifiers in each channel. The 5500's electronically balanced input is via a single 2510 op amp, while an API 2503 output transformer provides levels up to +30 dBm before clipping. If you prefer more "color" from iron, you can order an input transformer that provides true galvanic isolation from the outside world.
GET ON THE MIX BUS
As compared to most other EQs, equalizing full program mixes is a refined and rewarding process with the 5500--everything sounds API-good right away. I didn't perceive any loss or change when the 5500 was inserted into any processing chain, and I couldn't believe I'd hear just a 0.5dB change!
I used the Range switch like a depth control by first setting it to x1 (meaning ±2dB steps) to quickly find frequencies of interest, and then down to 1 or 0.5dB steps for just the right touch-up. Boosting at 15 kHz or even 20 kHz is smooth and glorious, although you will want to check your digital peak meters for occasional overs. Always a good test of an EQ, boosting +4 dB at 40 Hz on a mix proved the 5500 to be the clear winner with a much tighter bass sound as compared to the vintage 550Bs.
SOLID INSTRUMENT EQ
Equalizing individual drum mics proved the 5500 can get cranky, too. I wound +9 dB at 12 kHz (peak) on a well-used Shure SM57 snare drum mic. The drum had an old and badly flogged head, and the drummer was amazed at the sound I got. With that much boost, usually the source starts to sound more like the equalizer itself--not the case here. The snare drum was bright and open with lots of attack and punch. Kick drums with "boxy" peaks will easily benefit by notching in the 300 to 500Hz range and boosting at 30, 40 or 50 Hz.
Automated Processes Inc., 301/776-7879, www.apiaudio.com.
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