The API Audio 5500 circuit is based on the original 550 equalizer designed by Saul Walker, founder of Automated Processes Inc. Initially designed for console equalization, the 550 had limited functions due to console size constraints and used an unbalanced input. The 5500 overcomes these limitations with a balanced input, true straight-wire bypass, integrated power supply with noiseless muting, and range control for mastering applications.
API's commitment to analog purity is evident in the 5500, which uses hand-built 2520 Operational Amplifiers for gain and a 2510 Discrete Operational Amplifier for balanced input. The 2520, combined with the API 2503 output transformer, delivers a robust +30dBm before clipping.
The range control is an especially useful feature, allowing finer tonal adjustments with reduced amplitude control scales. This is particularly handy for complex program material, such as stems or submixes, and mastering applications.
API's hard-wire bypass ensures that power thumps are never heard, and the active balanced circuit and transformer-coupled output XLR deliver clean, distortion-free sound. The 5500 also includes a 1/4 inch input connector that interrupts any present signal on the XLR input, allowing for balanced or unbalanced sources without changing the gain or operating levels. With no polarity change from input to output, the 5500 is perfect for studios using either pin 2 or pin 3 as the "hot" connection.