Pass Labs X1 User Manual
pass
TM
Aug 10, 2006
X1 Owner’s Manual
X1 Owner’s Manual
1
Introduction
The X1 is an ultra high quality minimalist audio preamplifier that
features a remote control and external power supply. It combines
a completely new circuit topology with traditional construction
representing thirty five years of amplifier 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 X1
integrates power MOSFET and JFET devices in a simple Class A
topology in order to deliver the finest sound possible.
The patent-pending 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 X1 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 X1 employs a new type of volume control that offers an order
of magnitude better performance than seen before in an electronic
control. It provides over 60 dB of range, large voltage swing and
very good measured performance. Most importantly it is subjectively
outstanding; better than any potentiometer we know of. We are
justifiably proud of this new device, which is registered as having a
patent pending.
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.
Wayne Colburn,
X1 Owner’s Manual
Vice President, Design
2
Setup
The preamplifier main chassis / control unit has four sets of input
connections, both single-ended and balanced output connections, a
tape loop and a full function remote control that mirrors the front
panel functions.
The main chassis also has a DB-25 connector that connects to the
remote power supply and a single pair of 5-way binding posts that
are used for remote amplifier turn-on. The preamplifier’s voltage
and current rating are indicated on the bottom of the power supply.
It will be either 240 volts, 220 volt, 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 in all cases is 50 to 60 Hz. The
preamplifier typically draws 30 watts during operation. Please verify
that the pre-amplifier’s indicated voltage requirements are consistent
with the voltage available at your location, prior to operation.
The main preamplifier chassis is connected to the power supply
with a custom shielded cable that carries both the analog and digital
power. Please note this power cable must be installed before
the preamp is powered up. The power cable plugs, into and then
screws into, the rear panel of the main chassis and the power supply.
The connectors are a tight fit but should never need to be forced.
The X1 will function with either DB-25 on the power-supply chassis.
The additional DB-25 is for future performance enhancements.
We have provided a standard AC power cord that fits into the
IEC line receptacle at the right rear of the power supply chassis. The
preamplifier is equipped for operation with an earth ground which
is provided by the user’s AC outlet. Never defeat this ground, its
use will not adversely affect the performance of this product. The
chassis and circuit ground of the preamplifier are connected to earth
through a power thermistor, which gives a ground connection for
safety but helps avoid troublesome ground loops.
The X1 has a total of four inputs and a separate tape loop. Two
of the four inputs (Input numbers 1 & 2) can be used single-ended
or balanced. The other two inputs (inputs 3 & 4) 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 white spacers. Right channel RCA connectors are marked with
a red spacers. Balanced XLR inputs and outputs are marked with
“L” for left and “R” for right channel.
X1 Owner’s Manual
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If your signal source is unbalanced, input will always occur through
the RCA input connector. Inputs 1 and 2 give you a choice or either
single ended or balanced inputs. When single-ended inputs are used
on input 1 and input 2, a shorting plug, which is provided, should
be inserted between XLR pins 1 and 3 of the associated connector.
This plug shorts the negative input to ground thus optimizing the
input connection. You can run the X-1 without this shorting plug,
but performance will not be ideal. (NOTE: inputs 3 & 4 are single
ended only and do not have XLR’s associated with them.) You are
free to use any combination of balanced and unbalanced connections
with the X1. 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.
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 connectors 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 X1 takes maximal advantage of four identical gain paths (two
identical paths per channel) very much unlike the typical two gain
path (one signal path per channel) pre-amplifier you may be familiar
with. Almost without exception traditional audio pre-amplifiers,
unlike their science and industry counterparts, have maintained single
signal path per channel (two identical paths in a stereo pair).
In order to manage balanced signals these two gain path preamplifiers must utilize phase combining networks to process
incoming signals and subsequently drive outputs via phase splitting
circuits to re-establish a quasi-balanced signal. This manipulation of
signal typically adds additional gain stages and degrades the inherent
X1 Owner’s Manual
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