This VAC Statement dual mono triode vacuum tube phono (MM/MC, three gain modes, adjustable load, stereo/mono operation) preamplifier is designed for extreme applications. On the back panel there are two DC umbilical cords and large Amphenol aerospace connectors, a reminder of the massive dual mono power supply. There are inputs for four independent phone sources. In addition, each input may be of the conventional single-ended type or may be fully balanced.

Mechanical Design
The chassis is machined at VAC from high-grade, non-ferrous aluminum and with superior RF rejection properties across a wide range of radio frequencies. Similar care is taken around each of the six wideband audio transformers in each unit.

The front panel features a large machined knob for the four-position selector switch. Another large knob selects overall gains of 52 dB, 70 dB, or 76 dB to match virtually all moving magnet and moving coil cartridges. Smaller knobs provide full control of load impedance, load capacitance, and stereo or mono operation.

Electrical Design
The audio chassis’ distinct isolated sections dedicated to certain signal functions prevent unwanted interactions among the circuits. Interconnecting wires are carefully routed and directed by spaced machined nonmetallic guides. The hand-wired vacuum tube audio circuit assemblies are bonded to massive brass loading plates, which in turn are isolation mounted to the main chassis. The eight twin triode vacuum tubes employed in the various Class A 1audio stages are made with the finest grade parts, such as ‘naked’ metal foil resistors. The RIAA equalization is achieved without negative feedback, preserving the organic nature of the sound. A wide range of magnetic core materials and magnet wires were tested and auditioned, including different winding structures, silver and copper magnet wires, and mu metal and amorphous cobalt cores, to determine the ideal combination for the world’s finest phono stage.

Power Supply
The massive separate power supply is a dual mono design with substantial energy storage and high inherent regulation. Both resistive and inductive elements are used in concert with high-speed capacitor assemblies for the high voltage supplies, while active voltage stabilization is included in the four heater supplies and the 12-volt trigger supply.