Pass XA25 User manual

PASS®
XA25 25W Stereo Class A Amplier

WARNING
For your protection please read the following:
Water and moisture: This device should not be used near water ( as per example, near
a bathtub, washbasin, kitchen sink, laundry tub, wet basement or swimming pool ). Care
should be taken such that objects do not have the opportunity to fall, and that liquid is never
spilled onto or into the device enclosure through openings.
Power Sources: This device must be connected to a mains power source in strict accor-
dance with the supplied product owners manual. Please verify that the AC mains voltage
specied in the product manual matches those requirements indicated on the unit and the
AC voltage provided to your location by the power company. The product MUST be con-
nected to a MAINS socket outlet with a protective earthing connection.
Power Cords: Pass Labs provides a power supply cord that meets all legislated requirements
for the market in which the product was originally sold. If you choose to substitute an af-
ter-market product we urge you to choose one that is fully safety rated by the necessary local
authority.
Power supply cords should be routed so that they are not likely to be walked on, abraded, or
pinched by items placed on or against them, paying particular attention to cords where they
enter plugs or exit from a device. Never under any circumstance insert a cut or damaged
power cord into a mains power socket. Cables should never be connected / disconnected
with equipment powered up. Failure to heed this warning may damage or destroy equip-
ment.
To Disconnect the Amplier: To safely disconnect the amplier from the AC you must
remove the AC power cord from the amplier.
Ventilation: Power-ampliers run warm, but you should be able to place your hands on
them without discomfort. You must allow for this heat in installation, by providing for free
air circulation around the product. Leave a minimun of 6” of space around the amplier.
The ventilation should not be impeded by covering the ventilation openings with items, such
as newspapers, table-cloths, curtains, etc.
Other Warnings:
No naked ame sources, such as lighted candles, should be placed on the apparatus;
Mulitple speakers: If mulitple speakers are connected to the monoblocks, the total imped-
ance the ampliers sees should be 8 ohms or greater.
This amplier is sutable for tropical climates under 2000m and ambient temperatures of 40
degress C or less
Servicing: To reduce the risk of re, electrical shock or other injuries, the user should not
attempt to service the device beyond that which is described in the operating instructions.
All other servicing must be referred to qualied service personnel.

INTRODUCTION
Entering their 22nd year of production, the X and XA power ampliers have remained at the
cutting edge of audio through continuous innovation and renement. At Pass we build ampli-
ers with excessive output stages, huge heat sinks and massive power supplies. We use the highest
quality components in simple linear topologies, assembled and tested with great care in Auburn,
California. The measure well and sound great. They are heavy, reliable and expensive.
The new XA25 offers this at slightly lower power, without frills, at a lower price. It embodies
new components and innovative circuits coupled with the best elements of the previous genera-
tion.
The signal path from input to output has been simplied to fewer components. Degeneration,
“the other form of feedback” has been eliminated. The output stage consists of a single pair of
800 watt new generation output transistors operating push-pull Class A. We still use the same
“New Old Stock” of small power JFETs and cascoded MOSFET, in the classic “CFA” voltage
gain circuit. The amplier is still DC coupled and has no frequency compensation.
The result is faster, lower distortion, lower noise, higher damping and larger Class A operating
envelope into low impedance loudspeakers, all in a simple 3 stage circuit with total of three pair
of push-pull gain transistors.
In their ideal state, matched push-pull FETs give perfect “square law” cancellation of distortion,
an effect somewhat spoiled by degenerative Source resistance used to constrain the “personali-
ty” of the devices. The removal of this form of feedback is an important element in the per-
formance of the XA25 and is accomplished by new approaches to stabilizing gain and bias of
push-pull FETs.
This gives a lower output impedance, more gain, and lower spectral content of distortion, as evi-
denced by measurements (see the specs section), but the more important factor is the difference
it makes to the music.
We observed this difference some years ago in listening tests. Degeneration removed some of
the organic quality to the sound and so became the subject of further development work.
The XA25 measures superbly, but it’s subjective qualities are most special. In an industry where
products with great specs are frequently found to be dry and boring, this amplier breathes life
into the music.
Thank you for purchasing this product. Please enjoy.
Nelson Pass 12/20/16

SET UP
The XA25 measures 17”w x 17.4”d x 6”h and weighs 45 pounds. You may place it wherever
you please, but not directly on carpet - it is going to need lots of free air for adequate cool-
ing. There needs to be space above and unobstructed space around the sides to allow for
proper air ow. This is a factor in reliable operation and long life.
The XA25 is expected to have a 25-degree C rise at the sinks when running. Under normal
operation you should be able to grasp the heat-sinks for 5 to 10 seconds without heat being
an issue. If the amplier becomes too hot to touch please contact your dealer or the factory
for assistance.
AC power is provided by a conventional detachable IEC 320 grounded AC mains power
cord. This power cord serves as the safety disconnect. The power cord should be removed
from the wall in the event of electrical storms or when the XA25 is not going to be used for
long periods.
The amplier is designed to perform well with the included power cord. Should you select
an “after market” detachable power cord, please conne your selection to those rated by
local authorities to carry a minimum of 13A at 250V.
At idle the XA25 will consume 240W from the AC mains. The required voltage and correct
fuse value will be indicated on the rear of the amplier. Both 100 Vac and 120 Vac builds
are fused at 5A. The 220 - 240 Vac build ampliers are fused at 2.5 amp.
In all instances the fuses are type 3AG slow blow (time delay) fuse rated for 250 VAC ser-
vice. Do not substitute fuses of different values or physical size. If you cannot source
equivalent replacement fuses locally, please contact your dealer or the factory.
This product ships from the factory with a replacement fuse included in addition to the
fuse installed in the chassis fuse holder. The fuse holder is located on the rear panel of
the amplier. Changing the fuse requires a close tting straight blade screwdriver, and the
power cord should be unplugged from the wall. If you are not comfortable performing
this function in the unlikely event that it becomes necessary, please contact your dealer or a
service professional.
INPUT CONNECTION
The XA25 accepts a single ended (RCA / Cinch) input connector. The input impedance is
47 Kohm making the XA25 compatible with either tube or solid state line stage pre-ampli-
ers or source components with a built-in volume control.

OUTPUT CONNECTIONS AND LOUDSPEAKERS
The rear of the XA25 is equipped with a pair of Furutech binding posts for each channel,
four total. The binding posts are marked red and black.
The Red output connector connects to the Red (+) of your speakers and the Black connec-
tor will connect to the Black (-).
The Black output connector is at circuit ground. You can use it to connect to powered
sub-woofers if you like.
The amplier is stable into any load which does not dip below 0.5 ohms, but it will protect
itself by shutting off any channel which outputs more than 10 amps (200 watts peak into 2
ohms). The protection circuit is reset by turning the amp off for a few moments and then
turning it back on. We recommend that you check your output wiring and/or the loudspeak-
er if this happens, and contact your dealer or the factory if you have problems.
The Furutech binding posts deserve special note - in keeping with the requirements of Class
2 circuits in North America they are fully insulated. Speaker cables connected as intended
will have no exposed conductive metal. The Furutech posts accept banana, spade, bare wire
or pins with a diameter of 4.5mm or less. Bare wire, pins and spades socket into the binding
post only from the bottom. The nuts on the binding posts should only be nger tight. Nev-
er tighten with wrench or pliers.
NOTE - The Audio outputs of power ampliers are considered class 2 (CL2) circuits in
North America. This means that the wire connected between the amplier and the speak-
er(s) shall be rated at minimum Class 2 (CL2) and shall be installed according the the U.S,
National Electrical Code (NEC) Article 725 or Canadian Electrical Code (CEC) section 16.
OPERATION
Once the speakers have been connected in observation of the proper regulations and with
the observation of polarity and phase you may attach the input cables and power cord. It is
always advised that the power cord is the last connection made and the rst to be removed.
You are now ready to play music. Turn the level at the source or preamp to a low level.
Press the power switch on the front panel of the XA25, the blue LED above the power
switch will light. Turn the volume up to your preferred listening level. Sit back and enjoy!
The XA25 takes approximately an hour to fully warm up and sounds better as it does. Push-
ing the power button on the front panel of the XA25 a second time turns it off and extin-
guishes the blue LED.

XA25 Nominal Specications
Gain: 20 dB gain
Output power: 25 Watts rms @ 8 ohms
50 Watts rms @ 4 ohms
Distortion: 0.1% @ 25 Watts, 8 ohms, 1 KHz
Class A envelope: 50 Watt peak for 2, 4 or 8 ohm load
Bandwidth: DC to -2 dB @ 100 KHz
Noise: Less than 50 uV output, unweighted 20 to 20 KHz
Damping Factor: 500
Slew rate: 100 V/uS
Input Impedance 47 Kohm
Peak Current: 10 Amp output (200 Watt peak into 2 ohms)
Protection: Shutdown at 10 amps output
Idle Power draw: 2.0 Amps @ 120 VAC (240 Watts)
Here are some pretty pictures:

PASS®
Pass Laboratories Inc.
13395 New Airport Rd., Suite G, Auburn, CA 95602
voice: 530.878-5350 - fax: [phone] - web: passlabs.com
“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.
17.00
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UNLESS OTHERWISE SPECIFIED:
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PASS
PROJECT:
0.01, X.XX: 0.005
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DIMENSIONS ARE IN INCHES
TOLERANCE S:
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PASS LABORA TORIES
13395 New Airport Rd.
Suite G.
Auburn, CA 95602 XA25
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Warranty:
Please check with the factory authorized distributor in the country where you are purchasing
this product for specic warranty information.
All Pass Laboratories products purchased new from an authorized Pass Laboratories dealer in
North America are covered by a transferable, limited 3-year warranty. This warranty includes all
parts and labor charges incurred at the factory or factory specied repair facility, exclusive of
any subsequent or consequential damages. Damage due to physical abuse is specically exclud-
ed under this warranty.
For this warranty to apply the customer is responsible for returning the product unmodied to
the factory within the specied warranty period. The customer assumes all responsibility for
shipping and insurance to and from the factory or a factory specied repair facility. The con-
ditions and stipulations of this Pass Laboratories warranty only applies to units originally sold
new through an authorized dealer. Warranty on factory repair is 60 days and covers only the
scope of the original repair.
Non-North America customers should consult with their original Pass Labs dealer or distrib-
utor for warranty repair instruction prior to contacting the factory or shipping product to the
factory for repair.
Non-North American product must be returned to the country of origin for warranty service.
Foreign distributors are only required to offer warranty service on Pass Laboratories product
that they have imported, veriable by serial number.
Please note: Conditions of warranty service and customer rights for product purchased outside
the United States may vary depending upon the distributor and local laws. Please check with
your local distributor for specic rights and details.
Any modications to Pass Laboratories products that have not received written factory approv-
al nullify all claims and void all provisions of the warranty and liability by the maker or autho-
rized distributor. Should a modied product be returned to the factory for repair the owner will
be required to pay all necessary charges for the repair in addition to those charges required to
return the product to it’s original conguration.
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 suspect as counterfeit or stolen 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 international markets either
to authorized Pass Labs dealers or to third parties located in the United States or Canada.