API 550A 3-Band Equalizer
The legendary API 550A is a 3-band equalizer that has earned a permanent place in the history of recording. Originally designed by Saul Walker in the late 1960s, the 550A was one of the first modular OEM equalizers to be widely adopted by elite recording engineers and custom console builders like Frank DeMedio. Decades later, it remains a benchmark in the world of analog EQ — unmatched in tone, simplicity, and build quality.
Reintroduced in 2004 due to overwhelming demand, the API 550A continues to shape the sound of music across genres. With three overlapping EQ bands, each offering seven selectable frequency centers, the 550A delivers musical, repeatable tone-shaping with up to ±12 dB of boost or cut per band. Both the high and low bands can be switched between peaking and shelving modes, and an independent band-pass filter can be inserted via toggle switch for even more tonal control.
At the heart of the 550A is API’s iconic 2520 discrete op amp and its unique Proportional Q circuitry, which naturally narrows the bandwidth of EQ boosts and cuts at more extreme levels — allowing you to make bold moves without sacrificing musicality. This design, combined with the unit’s fully discrete topology and high headroom, makes the 550A an ideal choice for vocals, instruments, or mix bus applications.
Key Features:
- 3 bands of classic API equalization
- Each band offers 7 carefully chosen frequency centers
- Reciprocal and repeatable ±12 dB boost/cut per band
- Selectable peak/shelf mode on high and low bands
- Independent band-pass filter insert switch
- Proportional Q design for musical, narrow boosts and cuts
- Fully discrete analog circuitry with API 2520 op amp
- EQ “In” switch for silent engagement
- High headroom with +30 dB clipping level
Still considered one of the most musical and respected EQs ever made, the API 550A delivers legendary analog tone in a timeless design — a must-have equalizer for serious engineers and producers.