API550b 500-Series Discrete 4 Band EQ


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API 550b

The 550b 4-band equalizer from API is a direct descendent of the brand's classic and highly revered 550 EQ which is responsible for shaping the sound on a countless number of records since the 1960s. The 500-series version retains the circuitry and musicality of the historic equalizer, albeit now in a portable size so that you can take it anywhere you go. 550b is a device that is capable of both solving problems in recorded audio, and creatively coloring the sound, and it does it using a very stripped down intuitive interface. In fact, simplicity is a major strength of the 550b. There are four bands, each featuring a well-thought out selection of frequencies, and capable of up to ±12 dB boost or cut. Each band is controlled via dual concentric pots, where the blue knobs allows you to select the target frequency, and the silver one lets you attenuate or boost the signal in 2dB increments. Moreover, 550b is equipped with the API original "Proportional Q" design that intuitively widens or narrows the Q depending on the settings. Add to this an outstanding headroom, courtesy of the brand's proprietary 2520 op amp, and you've got yourself a professional studio tool that will wrap any signal you put through it in a cozy blanket of analog warmth.

550b Features

  • Four-band equalizer based on the classic API 550 module
  • Each band offers seven target frequencies carefully selected for their musicality
  • 12db boost or cut per band
  • "Proportional Q" narrows the filter width at extreme settings
  • Shelf/Peak switching on 1 and 4 EQ bands
  • Fully discrete circuitry
  • Number of Bands: Four
  • Filter Type: "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: ±12 dB
  • Filter Slope: 12 dB per Octave
  • Input Impedance: 18.5 K +4 in, 7.5 K -2 in
  • Output Impedance: Less than 75 Ohms
  • Nominal Levels: -15 to +15 dBu
  • Clipping Level: +30 dBu @ ±16 V
  • Frequency Response: +0, -.3, 30 to 20 kHz
  • Noise: Actual, unw noise, <-98 dBu, 20-20 kHz
  • Distortion: .07% max, @ +18 dBu Output
  • Connectors: 15 position .156sp edge connector
  • Power Consumption: ±12/18 Volts/DC,@ 40 ma.
  • Size: 1.5" X 5.25" X 7.5"
  • Weight: 2.02 lbs.
API 550b 500-Series Discrete 4 Band EQ Reviews