The Stax SRD-7SB is an electrostatic headphones transformer designed to operate Stax earspeakers without the need for AC power. It is a self-biasing model that draws bias power directly from a connected amplifier. The unit is compatible with Stax electrostatic headphones and allows users to enjoy high-quality audio in a home setup. The transformer includes a pass-through feature for loudspeakers and a switch to select the desired output. The SRD-7SB was made between 1979 and 1982 and has been noted for its excellent operational condition. When lightly used, it shows minimal cosmetic wear, making it appealing to those interested in vintage audio equipment. Specifications include an operational frequency response of 10Hz to 30kHz, total harmonic distortion rated at 0.02% at 100 V, and a bias voltage of 230VDC. The dimensions of the unit are 2.9 inches wide by 4.75 inches high and 8.5 inches deep, weighing approximately 3.75 lbs.
