As the industry rapidly embraced the sonic quality of the API 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.
Forty years later, the API 550A remains the standard against which other EQs are measured, and it has played a major role in the recording industry for decades. Still copied but never duplicated, the API 550A became API’s standard channel module EQ when the company began manufacturing consoles in 1971. With virtually all existing units spoken for, popular demand for this EQ resulted in API finally resuming production in 2004.
The API 550A provides reciprocal equalisation at 21 points in 5 steps of boost to a maximum of 12dB of gain at each point. The fifteen equalisation 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 equalisation 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 API 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 equalisation.
With the long-awaited reissue of this unit, an EQ that has had such a part in the history of recording is continuing to make history in today’s music.
Features
- 3 bands of classic API equalisation
- Each band offers 7 API selected frequency centres
- 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
