VAC PA-160 Owners manual

VAC PA160 "UNIVERSAL" MONOPHONIC POWER AMPLIFIER

Operating Instructions

Index:

Introduction2
Unpacking3
Installation3
Operation4
Bias Adjustment4
Fine Tuning Your System5

Operating Mode5
Feedback6
Ground Configuration Switch6
Load Impedance7
Sonic Troubleshooting7

Tube Selection8-10
Installing New Tubes11
Care of Chassis12
How to Contact VAC12
Specifications13
Location of Tubes & Controls14
Warranty Information15
Registration Form15

DO NOT OPEN THIS UNIT - THERE ARE NO USER SERVICEABLE
PARTS INSIDE. DO NOT REMOVE THE BOTTOM PLATES. LETHAL
VOLTAGES ARE PRESENT WITHIN THE CHASSIS. DO NOT EXPOSE
THIS UNIT TO MOISTURE OR OPERATE IT IF 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.

DO NOT PLUG INTO AN AC SOURCE UNTIL ALL CONNECTIONS ARE
COMPLETED.

1

Introduction

The PA160 is a wideband low-feedback monoblock power amplifier producing approximately 160 watts
per chassis in standard trim. It is largely based on the critically acclaimed VAC PA90C-1 circuit, which was
has been praised by many authorities since its introduction in 1990. This improved version delivers a new
level of performance, musicality, flexibility, and convenience.

Premium parts are employed throughout, including 14 pound 22 section bifilar-wound ultra-wideband
output transformers, polypropylene and polystyrene signal capacitors, high current rectifiers, low ESR power
supply, and proprietary wiring. The quality of parts and careful layout allows the use of very little or no
feedback for high sonic purity and low distortion.

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.

"Universal" is descriptive of the PA 160's ability to adapt to virtually any system context. Some of the
features of your power amplifiers include:

-configuration switches allow the use of KT88, KT77, KT66, 6550, EL34, or 6L6GC output tubes

-160 watts power output with the fabulous new Golden Dragon KT88 (standard)

-switch for triode, ultra-linear, or beam power/pentode modes of operation

-user variable negative feedback

-adjustable ground configuration switch to best compliment the associated preamplifier

-multiple impedance taps to match loudspeakers from 1 to 8 ohms from massive 21 section
wideband bifilar output transformers

-high current capability

-XLR and RCA input jacks for compatibility with balanced or single-ended sources

-simple front panel bias indicators and adjustments allow easy monitoring and optimum performance
(no meter required)

-balanced push-pull circuitry, with push-pull conversion in the first stage to better exploit the inherent
advantages of push-pull operation and to allow improved performance of the driver stage

-audio path completely hand wired, allowing components to perform nearer to the theoretical ideal

-non-magnetic chassis

-energy storage is distributed inside the chassis to place it nearer to the point of demand and
dedicated to particular uses, ensuring superior isolation of the various stages.

2

Unpacking

Do not lift the PA160 by the transformer cans!

Each tube socket on the amplifier is covered by a small round sticker. The color of this sticker corresponds
to the color of the sticker on a tube. Fit each tube into the matching socket, first
the tube and socket. Handle tubes by the
factory set, but should be checked during the installation procedure.

Installation

Physical requirements:

1)Provide adequate ventilation - allow at least 3 inches above and 1 inch to each side.

2)Do not place in a completely enclosed cabinet.

3)Do not stack other equipment on top of the VAC units.

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

5)The chassis and power transformers will become hot in normal use.

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

bases

, not the glass. The bias levels for the output tubes have been

removing

the sticker from

Electrical connections:

1)Complete all installation steps before plugging the amplifier into the AC mains supply.

2)Connect signal inputs to the power amplifiers. Single ended interconnect cables equipped with RCA
phono plugs or XLR cables (balanced or unbalanced sources) provide the input to each channel ­DO NOT CONNECT TO BOTH INPUTS AT THE SAME TIME.

3)Connect loudspeakers between the appropriate pair of binding posts on the back of the power
amplifiers. Most popular speaker cables can be accommodated by the output terminal strips. Output
impedance matching is available for loads of 2, 4, and 8 ohms. Connect one lead of the speaker
cable to the "G" position, and the other to either 2, 4, or 8. The "G" terminal is at ground potential,
and the amplifier does not invert phase.

4)Do not connect two amplifier outputs to each other.

5)Connect the AC cord to the power source indicated by the configuration card under the fuse (100
volts AC, 120 volts AC, 220 volts AC, or 240 volts AC at 50 or 60 Hertz).

6)Follow the BIAS procedure described in this manual to set the idle current. Check the idle current
at 1 minute, 30 minutes, 1 hour, and 2 hours. Also, read the section entitled INSTALLING NEW
OUTPUT TUBES.

7)Do not operate the amplifier unless connected to a loudspeaker or load resistor.

8)Do not switch on an
turn-on surge from an unmuted preamp could potentially damage the PA160, or cause the PA160
(or most high powered amplifiers) to deliver enough signal to damage the loudspeaker.

9)Check that the tube type switch is set to match the output tubes fitted.

unmuted preamplifier

or source component when the amplifier is operating. The

3

Operation

Continuous operation is not recommended. If the amplifiers will not be auditioned for a few hours it is best
to turn them off. This avoids undue stress to the KT88 output tubes, whose lives average between 3,000
and 8,000 hours depending upon brand fitted and random variations within the tubes themselves.

Do not operate the tube type switch while the unit is turned on.

As with all high fidelity products, the sound characteristics of the VAC amplifiers change somewhat as they
warm up. Good sound will be achieved within 15 minutes of operation, with subtle changes occurring for
up to one hour.

Please note that the initial break-in time of high resolution audio equipment is infuriatingly long. The PA160
will continue to season for at least 200 hours. Typically, the early sound of the amplifier will be less
extended, dynamic, and coherent. Then the sound will improve noticeable, followed by a period of darker
sound, finally giving way to the desired musicality. Patience, as they say, is a virtue.

Any time that the VAC Power Amplifier has not been used for a few weeks the sound may be different. This
is also normal for high resolution audio equipment. Optimum sound should return after a few hours. Also
be aware that many components display the need for a new break in period after being transported in
unheated cargo aircraft.

Bias Adjustment

Your VAC Power Amplifier has been shipped with output tube bias preset. This should be checked when
you install your amplifier, and periodically thereafter. It must also be set whenever an output tube is changed
or when the output operating mode is changed.

Adjustment of the output tubes is quite easy, and requires only a small screwdriver. On the front top of the
amplifier are four green LEDs, each with an adjacent adjustment control. Adjust the LEDs to be off, just
shy of green, when the amplifier is not playing music. To set, turn the control clockwise until the LED

begins

to glow green, and then back the control off

As music plays, the LEDs will flicker off and on. Check the bias if you ever see an LED stay green while
music is not playing, or if an LED does not illuminate when music is playing.

Any tube that can not be adjusted to the correct bias point should be replaced. Any tube which requires
constant readjustment should be replaced immediately. Never operate the amplifier with an LED that shows
green when music is not playing.

When installing new tubes, set the bias controls counter-clockwise. Check the bias of both channels as the
amplifier warms up - don't wait ten minutes.

Bias levels should be checked monthly to ensure optimum sound quality. It is not unusual for the bias to
change with time, particularly when tubes are new. The greatest amount of drift occurs during the first 200
hours of a tube's life. The drift may change direction periodically, such that the bias control must be
increased and later decreased, or vice versa. Check bias if the sound seems lacking in detail or dynamics.

slightly

until the LED goes out.

just

4