API 550B 500 Series EQ

The API 550B, a discrete 4-band EQ, played a significant role in the history of American music recording in the 1960s and 1970s. Initially designed for use in API's consoles, this latest "B" version of the 550 is a continuation of the original 1967 model, extending through the 550A with an additional filter band and several new frequencies. It seamlessly combines API's exclusive circuitry and proprietary components, including the renowned API 2520 op-amp, blending the past with the present. Countless hit records still rely on the distinct sound of the 550, making the 550B an indispensable tool you'll return to time and again. The API 550B is truly unique and unlike any other.

In an era where many EQs offer a multitude of complex features, the API 550B provides the right number of controls for professional engineers. Though it appears deceptively simple at first glance, the 550B's four EQ bands significantly overlap, making it versatile for both problem-solving and enhancing audio. Each band offers seven switchable filter frequencies that span 4 to 5 octaves, chosen through the expertise of the industry's top engineers. This reissued design closely follows the original blueprints and specification control drawings from the API archives.

By utilizing "API Proportional-Q," a concept introduced by API in the 1960s, the 550B intuitively widens the filter bandwidth at lower settings and narrows it at higher settings, eliminating the need for additional bandwidth controls. This feature minimizes the "phase-shift" effect often found in many equalizers. The reciprocal nature of the 550B allows users to reverse or adjust previous tonal modifications.

The API 550B is most appreciated by those who frequently work with EQ. Its ability to affect or undo tonal changes is a standout feature. When major tonal adjustments are necessary, the API 2520 op-amp's remarkable headroom delivers consistent and gentle "analog" performance even under pressure. With a remarkably wide range of tonal possibilities, the API 550B is an outstanding choice.