Pass Laboratories X2.5 Owner's Manual

pass

TM

Aug 10, 2006

X2.5 Owner’s Manual

X2.5 Owner’s Manual

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Introduction

The X2.5 is an ultra high quality linestage audio preamplifier
featuring remote control and internal power supply. It combines
a completely new circuit topology with traditional construction
representing thirty five years of preamplifier design.

This preamplifier flows from a commitment to create the best
sounding product: a simple circuit with the most natural sonic
characteristics. Derived from US Patent # 5,376,899, the X2.5
integrates power MOSFET and JFET devices in a simple Class A
topology in order to deliver the finest sound possible.

The Super-Symmetric gain circuitry is unique in providing superior
flexibility and performance with both balanced and unbalanced
inputs and outputs, converting one to the other as desired without
extra circuitry and without performance degradation.

The X2.5 minimizes the number of components in the signal path,
and yet retains exemplary objective performance specifications. It
pushes the edge of the art in exploring how much subjective quality
is obtainable with a new but very elementary gain stage.

The X2.5 employs a patented new type of volume control that
offers significantly better performance than seen before in an
electronic control. It provides over 60 dB of range, large voltage
swing and very good measured performance. The distortion and
noise is at 1/10 and the dynamic range 100 times the previous state
of the art in active attenuation. Most importantly it is subjectively
outstanding; better than any potentiometer we have evaluated.

The fluorescent display is a very special device. Not only will
you find its blue color highly attractive and readable, it is far more
reliable than the usual LED or LCD display.

Very few people are involved in the production of this product. I
supervise all phases of the construction, and I test each preamplifier
myself. If you have questions, comments, or problems, please feel
free to contact me directly.

Thank you for purchasing this preamplifier. It is my sincere hope
that you will enjoy its sound as much as I do.

X2.5 Owner’s Manual

Wayne Colburn

Vice President, Design

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Setup

The preamplifier has four sets of input connections, both single­ended and balanced output connections, a tape loop and a full
function remote control that mirrors the front panel functions.

It also has a 5-way binding post that is used for remote amplifier
turn-on. The preamplifier’s voltage and current rating are indicated
by affixed tag on the bottom of the preamplifier. It will indicate
either 240 volts, 220 volts, 120 volts, or 100 volts. A 0.5 amp 3AG
slow blow fuse is provided with 100-120 volt units, and a 0.25 amp
slow blow fuse is provided with 220-240 volt units. The frequency
rating of the power supply is 50 to 60 Hz. The preamplifier
typically draws 30 watts during operation. Please verify that the
indicated voltage requirement of this preamplifier is consistant with
the voltage at your location.

We have provided a standard IEC AC power cord that fits into
the IEC line receptacle at the rear of the preamplifier chassis.
The preamplifier is equipped for operation with an earth ground
provided by the users AC outlet. Do not defeat this ground. The
chassis and circuit ground of the preamplifier is connected to earth
through a power thermistor, which gives a ground connection for
safety but helps avoid ground loops.

There are a total of four inputs and a separate tape loop. Two
of the four inputs can be used single-ended or balanced. The
other two inputs are single-ended only. The tape loop has both
single-ended and balanced inputs and outputs. Balanced inputs
and outputs are via XLR connectors. Single-ended inputs and
outputs are via RCA connectors. On the XLR connectors, pin 1
is grounded, pin 2 is the positive signal, and pin 3 is the negative
signal. Left channel RCA connectors are marked with “L” from
below. Right channel RCA connectors are marked with “R” from
below. Balanced XLR inputs and outputs are marked with “L” for
left and “R” for right channel.

If your signal source is unbalanced, input will occur through the
RCA input connector, which is in parallel with the XLR connections
1 and 2. When single-ended inputs are used on input 1 and input
2, a shorting plug is provided between pins 1 and 3 of the XLR
connection, shorting the negative input to ground, and providing
optimal performance.

The unbalanced input impedance of the preamplifier is 33 kOhms.
In balanced mode, the input impedance is higher, with a differential
impedance of at least 66 kOhms.

X2.5 Owner’s Manual

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Next to the inputs on the rear panel, the preamplifier offers tape
inputs through both XLR and RCA connectors. This output is a
direct connection to inputs 1, 2, 3, and 4 when they are selected
from the front panel. Input 5 (TAPE IN) is deliberately not
available through the tape output connection. Input 5 is designated
for use with a tape recorder if you have one, and we have arranged
that it will not place its output on the tape out, which will prevent
you from accidentally creating a feedback connection with your tape
machine.

The main outputs are located at the left-hand side (viewed from the
rear) of the rear panel, two male XLR connectors, and two RCA
connectors, “R” (right) and “L” (left). The RCA connector’s ground
is in parallel with pin 1 of the XLR outputs and the RCA hot is fed
from an independent summing junction that maximizes the X circuit
benefits. The RCA, single-ended, outputs are buffered from the
balanced outputs. You may use both the single ended and balanced
outputs at the same time. On the XLR, pin 1 is ground, pin 2 is
positive, and pin 3 is negative.

The rear 5-way binding post can be used to turn on any X series
power amplifier.

Description of Operation

In application the X2.5s front panel controls and alphanumeric
display are quite straight forward, and intuitive. We encourage you
to become familiar with their operation prior to establishing any
input connections with this unit. Experience indicates that engaging
in a few minutes of exploration and playtime will add much to your
ultimate enjoyment of this exceptional Pass Labs product.

The two front panel mode switches move the preamplifier and it’s
display through 10 different functions. From left to right these
functions are as follows: Volume, Input, Mute, Tape, Balance,
Display, Mono, Unity, Amp (power-amplifier control), and Gain.
Actuating the mode < switch moves the function to the feature
immediately to the left, and conversely actuating the mode > switch
moves the function to the feature that is immediately to the right.

The two Select switches (designated by up and down pointing
arrows) then alter the displayed active function. The select arrows
toggle the following functions either off or on (the up pointing
arrow representing “on” and the down pointing arrow representing
“off ”) Mute, Tape, Mono, and Amp.

X2.5 Owner’s Manual

The leftmost function as selected by the two mode switches is

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