VAC Phi 220 - Manual (Page 4)

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INTRODUCTION
The Phi Beam Power amplifiers are unique power amplifiers, and the most power and detailed in
VAC’s history. Excellent linearity is achieved without resorting to loop negative feedback, for a more
natural, dimensional sound.
A total of four KT88 are used in Class A1. Uniquely, each is provided with a separate DC heater
supply to ensure that no undesirable couplings occur; only the intended ideal signal path exists.
The input circuitry of the Phi is derivative of the unique Williamson circuit, which provides pure,
direct coupled, inherently balanced input amplification and phase splitting. Type 6SN7/5692 octal
twin triodes do the honors.
Two superb VAC output transformer, interconnected in a way that allows high power to be
delivered with the sonic purity of low power devices, provide superb voltage/current translation,
allowing impedances from eight ohms to as low as one ohm to be driven.
The main chassis is machined from thick aluminum. The separate power supply allows e.m.f. fields,
switching transients, and mechanical vibration to be isolated from the audio circuits. The high
voltage supply utilizes dual choke pi filtering for extremely low noise.
The Phi Beam Power amplifiers are designed not to the latest fad but to substance, for the highest
possible sound quality. Time spent familiarizing yourself with this manual will be well rewarded.