Quadrature Z

About the Quadrature Z

The David Berning Company Quadrature Z is a high-power, output-transformerless (OTL) vacuum-tube monoblock power amplifier using Berning’s patented ZOTL (Zero-Hysteresis/impedance-conversion) technology. Its “Quadrature” impedance-conversion system interleaves parallel conversion processes with phase overlap to eliminate conversion dead time, providing unusually tight coupling between the output tubes and loudspeaker. The design was intended to combine OTL transparency with the ability to drive demanding, relatively low-impedance speaker loads. It uses four 33JV6 output tubes, a triode-connected screen-drive arrangement, a regulated resonant switching power supply with power-factor correction, automatic bias control, and extensive protection circuitry. A three-position feedback switch allows the user to alter feedback, output impedance, and damping characteristics. The amplifier is supplied as a mono unit, so stereo operation requires two amplifiers.