VAC PA90 - Manual (Page 3)

3
INTRODUCTION
Your VAC Power Amplifier is designed not to the latest fad but to substance, providing the
highest quality of sound. Time spent familiarizing yourself with this manual will be well
rewarded.
Figure 1 demonstrates the way to connect the VAC amplifiers and power supplies. A single
PA90 is connected to a PS90 to form a 120 watt monophonic amplifier.
Some of the features of your power amplifiers include:
The maximally balanced push-pull circuitry, with push-pull conversion (phase inversion)
occurring in the first stage, better exploits the inherent advantages of push-pull operation and
allows improved performance of the driver stage.
Modest loop negative feedback (8 dB) ensures better dynamics, gentle clipping, and superior
overload recovery. Simple feedback arrangement avoids unnecessary multiplication of the order
of distortion products.
Completely hand wired in three dimensional space for the shortest possible lead lengths,
allowing passive components to perform much nearer to the theoretical ideal.
All chassis are machined 1/8 inch thick aluminum, creating an extraordinarily rigid non-
magnetic platform that is unusually resistant to vibrations that could mar the sound.
Mechanical vibration from the power supply is completely isolated from the amplification
circuitry due to the multiple chassis design.
Energy storage is distributed among the chassis to place it nearer to the point of demand and
dedicated to particular uses, ensuring superior isolation of the various stages.
Output stage is based on the KT77 Beam Power tube or the EL34/6CA7 Power Pentode
operated in Class A at 54 milliamperes idle current per tube.
Output stage may be operated in partial-triode (ultra-linear) or full triode mode, selected via a
single switch.
Impedance matching taps are provided for 2, 4, and 8 ohms.