API 550a

Discrete 3 Band EQ
Few equalizers enjoy the respect and admiration of the coveted API 550A. Designed by the now-legendary Saul Walker in the late '60s, the discrete 550A was first used as a modular OEM equalizer. As the industry rapidly embraced the sonic quality of the 550A, it quickly found its way into many custom console designs by Frank DeMedio and other leading engineers. Many of these consoles are still in use today.

The 550A provides reciprocal equalization at 21 points in 7 steps of boost to a maximum of 12dB of gain at each point. The fifteen equalization points are divided into three overlapping ranges. The high and low frequency ranges are individually selectable as either peaking or shelving, and a band-pass filter may be inserted independently of all other selected equalization settings. Frequency ranges and boost/cut are selected by three dual-concentric switches, and a pushbutton "in" switch allows the EQ to be silently introduced to the signal path. A small toggle switch is used to insert the band-pass filter into the 550A.

The combination of Walker's incomparable 2520 op amp and his "Proportional Q" circuitry gives the 550A user an uncomplicated way to generate acoustically superior equalization.

Features:
    3 bands of classic API equalization
    Each band offers 7 API selected frequency centers
    Reciprocal and repeatable filtering
    Maximum 12 dB of boost/cut per band
    EQ Band 1 and 3 offer shelf/peak switching
    "Proportional Q" narrows filter Q at extremes
    Traditional API fully discrete circuit design
    High headroom +30 dB clip level

Technical Specifications:
    Input Impedance:     66 kΩ high level, 17 kΩ low level
   Output Impedance:     Less than 85Ω (transformer isolated)
   Nominal Operating Level:     –15 dBm to +12 dBm
   Insertion Loss:     None (bridging)
   Frequency Response, Unequalized:     ±0.5 dB 30 Hz to 20 kHz
   Noise:     Unequalized, output noise of –90 dBm, high level strapping and, –98 dBm, low level strapping, 20 Hz to 20 kHz unweighted
   Distortion:     .05% THD max, 30 Hz to 20 kHz @ +4 dBm, .07% THD max, 30 Hz to 20 kHz @ +18 dBm
   Clipping Level (3% THD):     +30 dBm
   Power Requirement:     ±15 volts to ±18 volts @ 70 ma
                        Toggle Switch:50 Hz to 15 kHz band-pass filter In or out
                        Push Button: LF range Peak or Shelf
                        Push Button: HF range Peak or Shelf
                        Push Button: Equalization In or Out
                        Tally light when In
   Connector:     30 pin PC connector supplied
   Size:     1.5" X 5.25" X 7.75" Deep
   Size (Boxed for Shipping):     4.5" X 6.25" X 10.25"
   Actual Weight:     2 lbs.
   Shipping Weight:     2.53 lbs.