VAC Phi Alpha Preamplifier User Manual

F

The VAC Phi Alpha

Triode Preamplifier

Operation & Maintenance Information

Valve Amplification Company

Manual issued 02/15/2008

CAUTION

THE PREAMPLIFIER AND POWER SUPPLY CONTAIN POTENTIALLY LETHAL VOLTAGES, AND
TUBES THAT BECOME HOT IN USE.

NEVER OPERATE THE PREAMPLIFIER OR POWER SUPPLY WITH THE COVERS REMOVED.

DO NOT REMOVE THE CHASSIS COVERS EXCEPT TO CHANGE TUBES OR LIGHT BULBS.

BEFORE OPENING A CHASSIS TO CHANGE TUBES OR LAMPS, DISCONNECT THE POWER
SUPPLY FROM AC POWER AND THE AUDIO CHASSIS FROM ALL OTHER COMPONENTS.
ALLOW IT TO SIT TURNED OFF FOR 30 MINUTES BEFORE REMOVING THE COVER. REPLACE
COVER AND SECURELY ATTACH BEFORE RECONNECTING AND OPERATING

DO NOT OPERATE THE UNITS IF THEY ARE WET.

VACUUM TUBES BECOME HOT ENOUGH TO CAUSE SERIOUS BURNS. NEVER TOUCH A TUBE
WHEN THE UNIT IS ON. IT MAY TAKE SEVERAL MINUTES FOR THE TUBES TO COOL DOWN
AFTER THE UNIT IS SWITCHED OFF. IT IS STRONGLY RECOMMENDED THAT THE TUBE COVERS
BE LEFT IN PLACE AT ALL TIMES.

THE AMPLIFIER AND POWER SUPPLY ARE HEAVY. IT IS ADVISABLE TO HAVE ASSISTANCE IN
UNPACKING, MOVING, AND SETTING UP. BE SURE TO USE PROPER LIFTING TECHNIQUES TO
AVOID BACK STRAIN AND INJURY. BE CERTAIN TO INSTALL IT IN A SECURE LOCATION FROM
WHICH IT CAN NOT FALL OR TIP OVER.

CONTENTS

Introduction
Installation
Inputs (back panel)
Outputs & Grounding Switch (back panel)
Operation
Fuses
Front Panel Controls
Remote Control
Replacement of Tubes
Care of Chassis
A Word About Tubes In General / Locating a Defective Tube
Warranty / Registration Form

1

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 A1 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.

2

INSTALLATION

1)Provide adequate ventilation.

2)Do not operate on carpet or any other surface that might block air flow.

3)The chassis will become warm in normal use.

4)Do not allow the chassis to touch any metal parts, such as the frame of an equipment
rack. This might create a parallel ground path that could degrade the sound of your
system.

5)Input connection is via single ended RCA jacks or XLR jacks (which can be from
balanced or unbalanced sources). For the inputs that can accept either XLR or RCA
connectors, be sure that the associated switch is set correspondingly. Connect line
level inputs (CD, Tuner, Tape, etc.) to the appropriate RCA input jacks on the rear
panel. Note: with the exception of Phono (when fitted), all inputs are "line level."

6)Output to the power amplifier can be single-ended on RCA jacks or balanced on
XLR jacks, but not both simultaneously. The output mode switch must be set to
match the connections used. IMPORTANT: READ THE SECTION ON "OUTPUTS &
GROUNDING SWITCH."

7)Output to a recording device (tape recorder, CD recorder, etc.) may be obtained
from the “TAPE OUT” jacks. The adjacent switch for “TAPE OUT” must be set to ON.
If your system does not have a recorder, this switch should be set to OFF.

8)For optional phono stage only: Connect phono cables to the rear panel MM and/or
MC inputs labeled "Phono" (both may be used in the same system, as they are
switched by a control on the front panel). Connect the ground wire(s) from the
turntable(s) or phono cable(s) to the "Ground" terminal provided on the rear panel.

9)Connect the power cable from the power supply to the preamplifier. Be sure to
insert the connector properly, and fully tighten the locking screws.

10)Connect the power supply to the power source indicated on the rear panel, either
100, 120, 220, or 240 volts AC. The voltage is set at the factory. Avoid power
conditioners that float the ground pin. ALWAYS connect power cord to component
before plugging it into an AC outlet. For best performance, try to route the power
cord away from signal cables.

3

11)Pay close attention to power quality, and be aware that different power cords can
alter the sound. The power supply’s backlit meters show variation in power line
voltage as reflected to the audio circuitry.

12)12 volt triggers are provided for control of other audio components.

4