API 550B 4-Band Equalizer – 500 Series

The API 550B is a classic 4-band equalizer in the compact and versatile 500 Series format, offering the legendary tone and design heritage of API’s original 1967 550 EQ — now with an added fourth band for enhanced tonal control. Perfect for tracking, mixing, or mastering, the 550B delivers musical, repeatable EQ shaping with the unmistakable analog warmth and punch API is known for.

Each of the four bands provides seven carefully selected frequency centers, chosen by API engineers to deliver musical results across a wide range of applications. With up to ±12 dB of boost or cut per band and the renowned “Proportional Q” design, the 550B naturally adjusts the bandwidth of the filter — wide at subtle settings and narrower at more extreme boosts or cuts, making it easy to dial in precise tonal shaping that always sounds natural.

Bands 1 and 4 can be switched between peak and shelving modes, further extending the unit’s flexibility for bass, vocals, guitars, and mix bus duties. Built with API’s fully discrete analog circuit design and featuring the iconic 2520 op amp, the 550B offers incredibly high headroom, with a clip point at +30 dB — perfect for today’s high-resolution audio workflows.

Key Features:

Four bands of classic API equalization
Each band offers seven API-selected frequency centers
±12 dB boost/cut per band
Bands 1 and 4 offer peak or shelf switching
“Proportional Q” design for musical, natural EQ curves
Fully discrete circuit design with API 2520 op amps
Reissue of the 1967 API 550 EQ with added fourth band
High headroom design with +30 dB clip level
Fits all standard 500 Series racks

The API 550B combines vintage EQ character with modern flexibility, offering legendary API tone in a powerful and intuitive format — a must-have equalizer for any serious engineer working in the 500 Series environment.