Pass Laboratories X2.5 Manuale utente

X2.5 Owner’s Manual

passTM

X2.5 Owner’s Manual

Aug 10, 2006

X2.5 Owner’s Manual

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.

Wayne Colburn

Vice President, Design

Introduction

X2.5 Owner’s Manual

The preamplifier 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.

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.

Setup

X2.5 Owner’s Manual

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.

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.

The leftmost function as selected by the two mode switches is

Description of Operation

X2.5 Owner’s Manual

volume, and the up/down arrows select 32 steps incrementally,

indicated on the display as 0 - 31. A more traditional knob, located

at the far right of the front panel, which is always active, exactly

duplicates this control function.

The next mode to the right is the input selector, for inputs 1

through 4. Input 4 is unique in that it is linked with the Unity

function. (The UNITY FUNCTION is discussed at length later in

this manual.) The two select arrows logically control selections of

the various inputs to the preamplifier.

The channel balance function is affected by the up and down

arrows. The up arrow is balance right and the down arrow

conversely balance left.

The display function has three iterations of brightness selectable by

the up/down arrows; they are bright, dim and off.

The unity function bears special attention. This control is associated

only with input number 4 and has two positions selected with

the up/down arrows. The up arrow toggles to a straight through

function with neither attenuation nor gain. This function is useful

in that it allows the preamplifier to function as a unity buffer for use

with components that best function with their own volume controls,

such as surround processors. When the right-front and left-front

outputs of the processor are routed through input 4 of the X2.5

(with the gain of the X2.5 set for Unity gain), the volume will be

under full control of the processor and the X2.5’s action will be

totally transparent. When the user chooses Unity this sets the X2.5’s

gain to the low (+4dB) setting, regardless of how it was previously

configured. When at Unity both left and right level controls

on the X2.5 will have a displayed value of 24, and any previous

balance settings will be lost. Both of these default conditions are

intentional, and intended to make the most advantageous use of

your source electronics. You may also set any input to unity by

selecting low gain and setting the volume at 24.

Before selecting this option, it is imperative that the input device on

input number 4 has its gain set to minimum. Failure to follow this

precaution could result in a volume level intolerable to both ears

and speakers. To further protect your hearing and valuable audio

equipment, Wayne has designed this product, so that the volume

setting of the preamplifier will always revert to zero as you change

inputs. We trust that the remote control, with its four buttons that

duplicate those of the preamp front panel will enable you to quickly

select inputs and establish levels of output.

X2.5 Owner’s Manual

The rear mounted pair of five way binding posts are intended to

control the on/off function of our own X series power amplifiers

from the X2.5 front panel, or via the four button remote. When

the preamp mode “Amp” is selected it allows the user to switch a

nominal 12 volts DC at maximum draw of 50 milliamps to these

binding posts. In some instances this voltage may have the ability

to control products from other manufactures, but we by no means

have comprehensive listing of their compatible features. If you have

questions about compatibility your service technician and dealer are

an excellent resource of information.

The X2.5 to our knowledge is unique in that its gain may be

attenuated to match the requirements of a wide variety of

electronics and speakers. The gain control toggles between two

settings, offset from one another by 10 dB. The up pointing arrow

selects +14 dB and the down pointing arrow selects +4 dB. When

used with our own X series power amplifiers, which are quite high

gain (30 dB), we find the +4 dB setting to be most satisfying. With

other product we suggest that you let your ears determine which

setting conveys the most sonic benefit.

The remote control uses the same four-button system. The far left

button is mode < left the far right button is mode > right. The

top button is select ^ up and the bottom is select v down. The

display shows the active function. The display has two brightness

levels and off. If any control is used the display reverts to the last

level. The off mode shows the display for about 7 seconds and

then turns off.

The electronic volume control allows greater than 60 dB range

and is driven by a micro-controller that reads the optical encoder

serving as a front panel volume control. In this manner tracking of

the volume of the two balanced channels is possible with accuracy

unavailable on any ordinary volume control, assuring precise level

steps and high common mode rejection in balanced circuits. Wayne

Colburn’s exceptional volume control in conjunction with the

fluorescent display give the user ability to replicate volume levels

with absolute accuracy in steps of roughly 3dB.

1) Circuit simplicity and a minimum number of components is

a key element. The fewer parts in series with the signal path, the

better. Adding more parts and gain stages may improve measured

specs, but will seldom improve the perceived sonic quality or

reliability of a product.

Product Philosophy

X2.5 Owner’s Manual

2) The characteristic of gain devices and their specific use is

important. Individual variations in performance between like

devices are important, as are differences in topological usage. All

signal bearing devices contribute to the degradation, but there are

some different characteristics that are worthy of attention. For

example, smooth low order nonlinearities are additive in quality,

bringing false warmth and coloration, while abrupt high order

nonlinearities add harshness and false brightness.

3) Maximum intrinsic linearity is desired. This is the performance

of the gain stages before feedback is applied. Experience suggests

that feedback is a subtractive process; it removes information from

the signal. In many older designs, poor intrinsic linearity has been

corrected out by large application of feedback, resulting in loss of

warmth, space, and detail. The trick is to get good performance

without this excessive reliance on feedback.

The art of high end audio design lies in the approach to combining

these elements to get high reliability and simplicity, high quality

measured performance, and high quality subjective performance. It

takes imagination and hard work to get as much of these as possible

at once without trading them off against each other.

We recommend the use of the balanced output mode where

possible. It will retain the character of the input mode, but offers

less distortion, less noise, more gain, and more voltage swing,

without compromising the sound.

With balanced operation, the common mode rejection of the

preamp reflects the intrinsic common mode rejection of the

topology, the matching of the gain devices, and the matching of

the attenuator channels. In this case we have been able to keep

the total mismatch to about .1%, for a common mode rejection of

approximately -60 dB.

The input system of the preamplifier will exhibit full common mode

noise rejection with passive balanced sources, where the negative

input is connected to ground at the source through the appropriate

source impedance. This allows adaptation of unbalanced sources to

balanced operation with passive cable connections in a manner that

achieves the noise rejection of active balanced sources.

The use of a micro-controller allows all of the preamplifier

functions to be repeatable and accurately controlled. The micro

processor only controls the functions of the preamplifier. At no

Other Design Comments

X2.5 Owner’s Manual

time does any of the input or output signal come into contact with

the digital control signals. The digital circuits are powered by a

power supply that is completely separate from the analog supply.

Should it ever be necessary to update the software that controls the

functioning of the preamp only the socketed micro processor need

be changed.

The power supply for the X2.5 consists of a toroidal power

transformer delivering an unregulated +/- 45 volts which is actively

regulated before feeding passive filtering and powering the constant

current sources which bias the gain stages. Each channel has it’s

own regulation. The power supply noise reaching the circuit is on

the order of one microvolt, and the little of that which get through

the circuit is rejected at the output in a balanced system. The relays

and control systems are regulated independently, and all digital

circuitry is isolated from the power supply.

Muting relays, which delay connection during turn-on and shut off

the output when insufficient power supply is available to maintain

regulation, guard the output of the preamplifier. The preamplifier

is designed to run constantly, and will exhibit optimum measured

performance within about 10 hours of turn-on.

The X2.5 consists of a single chassis.

For more information please contact:

Pass Laboratories Inc.

P.O. Box 219,

24449 Foresthill Rd.,

Foresthill, CA 95631

Tel: 530.367.3690

Fax: 530.369.2193

www.passlabs.com

X2.5 Owner’s Manual

Gain, Balanced selectable 4 dB

or 14 dB output

Gain, single-ended selectable 4 dB

or 14 dB output

Freq. Response -3 dB @ 2 Hz

-3 dB at @ 100 kHz

Distortion @ 1KHZ < .1 % THD, typically

.003% @ 2 volts

Maximum Output 10 volts rms. bal out

7 volts rms. unbal

Output Impedance 200 ohms unbal

750 ohms balanced

Input Impedance 33 kOhm unbal

66 kOhm balanced

CMRR typ. -55 dB, 1KHz

Crosstalk typ. -85 dB, 1KHz

Output Noise floor < -125 dBV, 20Hz

to 20 KHz

External amp turn on 12 volts DC 50 mA

continuous

Power Consumption 35 watts

Dimensions 17” W x 11.5 “D

x 3.5”H

Shipping Weight 28 Lbs in packing

X2.5 Specifications

“Pass”, “pass”, “Pass Labs”, “Pass Laboratories”, Supersymmetery”,

“Aleph”, and “Zen” and are all registered trademarks of Pass

Laboratories, Inc., and all rights thereto are protected by law.

X2.5 Owner’s Manual

Please check with the factory-authorized distributor in the country you are

purchasing this product for specific warranty information.

All Pass Laboratories products purchased from an authorized Pass Labora-

tories dealer in North America are covered by a transferable, limited 3-year

warranty. This warrantee includes all parts and labor charges incurred at the

repair facility in addition to return shipping to the domestic customer, exclu-

sive of subsequent damages. Damage due to physical abuse is specifically

not covered under this warranty.

For this warranty to apply the customer is responsible for returning the

product unmodified to the factory within the warranty period. The customer

assumes all responsibility for shipping and insurance to the factory or a fac-

tory specified repair facility. The conditions and stipulations of this Pass

Laboratories warranty only applies to units sold new in North America.

Non-North America customers should consult with their original Pass Labs

dealer or distributor for warrantee repair instruction prior to contacting the

factory or shipping product for repair.

Non-North American product must be returned to the country of origin for

warrantee service. Foreign distributors are only required to offer warranty

service on Pass Laboratories product that they have imported.

Please note: Conditions of warranty service and customer rights for product

purchased outside the United States may vary depending upon the distribu-

tor and local laws. Please check with your local distributor for specific rights

and details.

Any modifications to Pass Laboratories products that have not received

written factory approval nullify all claims and void the warrantee. Should a

modified product be returned to the factory for repair the owner will be re-

quired to pay all necessary charges for the repair in addition to those charges

required to return the product to it’s original configuration.

In the case of safety issues, no product shall be returned to the customer

without those safety issues being corrected to the most recent accepted

standards.

Removal or alteration of original Pass Labs serial numbers voids the factory

warranty. Product with altered or missing serial numbers will be suspected

as counterfeit product.

Pass Laboratories will not repair or in any way indemnify any counterfeit or

cloned product.

Pass Laboratories does not offer products in voltages intended for inter-

national markets either to authorized Pass Labs dealers or to third parties

located in the United States or Canada.

Warranty Information

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