VAC Phi Alpha Preamplifier User Manual
Page 3
2
INTRODUCTION
The Phi Alpha Preamplifier is the world's finest audio preamplifier and an absolutely unique
component. Its unusual topology, premium parts, and flexibility make it a pleasure to hear
and operate.
The line stage is, in effect, a small Class A
1
power amplifier, capable of driving loads as low
as a few hundred ohms. This is a stark contrast to normal preamplifiers, which claim a low
output impedance but completely collapse when asked to deliver current. The Phi circuit
is loafing with a normal load in the 10,000 to 200,000 ohm range, delivering an effortless,
musical performance.
There is no loop feedback and no coupling capacitors in the line section. All active
elements are triode tubes, the purest, most linear amplifying devices yet invented. Output
matching is accomplished by way of superb output transformers. As a side benefit, different
output grounding configurations are possible, optimizing performance into either balanced
or single-ended loads, and allowing ground loops to be broken.
The optional phono stage uses triode tubes operating without loop feedback. Gain is
moderately high, with a very low noise floor. Low output MC cartridges are accommodated
by means of high quality matching transformers, which contribute voltage gain without noise,
resulting in detail that emerges from a remarkably dark and neutral background.
Remote volume control is implemented via a motorized mechanical device. This provides
two major advantages. First, the control is completely intuitive to use. Second, we avoid the
sound degradation attendant with VCAs, transistor switches, and switched resistor arrays.
Each chassis is fabricated from non-magnetic aluminum. The separate power supply allows
e.m.f. fields, switching transients, and mechanical vibration to be isolated from the audio
circuits.
The Phi Alpha Preamplifier is 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.