Pass Xs Owner's Manual
PASS
TM
Xs Preamp Owner’s Manual
Sept. 2013
Xs Preamp Owner’s Manual
1
Introduction There are people who do not know that Wayne Colburn has
designed the Pass Labs preamplier products for the last 20 years.
Wayne’s modesty has tended to keep him out of the spotlight, and
he does not like to write, and so it falls on me to trumpet his latest
achievement. It follows in a smooth progression of successful preampliers and phono stages, each recognized as offering a genuine
improvement in sound quality.
When we began development of the Xs power amplier ve years
ago, we knew that we would also need a companion piece. Of
course, back then we thought we could have this done in a year or
so...
Wayne was given carte blanche on the design and an unlimited
budget, and as progress on the amplier was very slow, he had lots
of time to acquire and play with many exotic parts and materials.
And spend money.
Naturally the comparison will be made with its predecessor, the
XP-30 line stage preamp, which achieved incremental performance
improvements over the XP-20 and XP-10. The most obvious
difference is that the Xs comes in only two chassis, where the XP-30
had at least three chassis, one for supply and control, and one chassis
per channel for as many channels as you might reasonably want. The
Xs is designed solely for two channel operation, and it ts in two
(larger) boxes.
The XP-30 had a few unique features, among them independently
adjustable dual output sets for use in bi-amping and the high voltage
output swing capable of driving unity gain power ampliers such as
the First Watt F4.
The Xs preamp expands on these features and adds some nice new
touches, such as remote control of the absolute phase switching.
The volume controls are improved in performance with 0.5 dB steps,
expanded dynamic range and lower noise. The harmonic content of
the 0.001% distortion gure of the volume control has been tweaked
to favor 2nd harmonic over 3rd. The buffer stage for the volume
control has been eliminated, giving an even simpler gain path.
Improved circuit boards layout puts the cherry on top.
The gain stages still use matched complementary Toshiba Jfet inputs,
Bipolar cascodes, and Mosfet outputs. Pass Labs has some of
the few remaining stocks of these largely unavailable parts. Some
changes have been made – the Class A bias has been doubled,
Xs Preamp Owner’s Manual
2
For your protection please
read the following:
accompanied by much larger heat sinks, and the circuit will now drive
any reasonable load (I have successfully used it to drive my 16 ohm
Lowthers).
The circuits are now completely DC coupled throughout (no
capacitors), and the frequency response is at to 100 Khz.
The XP-30 could swing enough voltage to drive a balanced follower
output stage to 80 watts rms. The Xs increases that gure to over
150 watts.
Some of the materials have gotten more exotic – the gain stages are
mounted on ceramic circuit boards with gold plating. The channel
motherboards are made of Panasonic Megtron with immersion gold,
which performs about as well as Teon or Polyamide but without
the adhesion properties. The power supplies use 4 ounce platedthrough high temp FR406.
While the two channels share a chassis, they are isolated on separate
board systems with distance between them, so the crosstalk gures
between channels are as good as the XP-30 separate chassis. Each
channel and the digital control circuits have their own isolated
supplies, each mounted on it’s own board in a separate chassis.
The three separate power supplies use the lowest noise transformers
available from Plitron and they incorporate EMI lters on the AC
line input, secondary output, fast/soft recovery rectiers, large
storage capacitance and extensive regulation. The active regulation is
both series and shunt types, and is followed by passive ltering using
polypropylene capacitors.
All this in machined aluminum cases. If like me your eyesight is not
what it once was, you will also appreciate the larger display on the
control panel.
It does not automatically follow that more money and more exotic
parts and such will result in a better sounding product. Indeed,
some of things Wayne tried did not work as hoped, although they
measured well enough. Fortunately there was lots of time available,
and the back-and-forth process between Wayne and the four other
listeners assured the nest product we could possibly make.
At this point, I can only say that if you are on a restricted budget you
might be wise to avoid borrowing one of these.
Xs Preamp Owner’s Manual
Nelson Pass 2013
3
WARNING, IMPORTANT SAFETY INSTRUCTIONS
Read these instructions, Keep these instructions
Heed all warnings, Follow all instructions and precautions
Water and moisture: Electrical devices should never 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. Electrical devices should never be
left exposed to the weather, dampness, splashing or dripping. Clean this
device only with a dry cloth.
Power Sources: An electrical device must be connected to a mains power
source in strict accordance with the supplied product owners manual and
local standards. Please verify that the AC mains voltage specied in the
product manual match those requirements indicated on the unit and the AC
voltage provided to your location by the power company.
Grounding: Adequate precautions should be taken so that the grounding
provisions built into an electrical product are never defeated. This product
is supplied with a polarized and grounding type IEC 320 power cord. An
IEC 320 grounding power cord has two blades, which conduct power and
a third grounding prong. The grounding prong is essential for personal
safety and proper operation of this product. If the grounding prong does
not t your outlet, please consult an electrician and have the obsolete
receptacle updated before operating this device.
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 after-market product we urge you to
choose one that is fully safety rated by the necessary local authority.
The mains cord is intended to function as the safety disconnect for this
product and must remain readily accessible for this purpose at all times.
Power Cord Protection: 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, or where they intersect trafc paths. Never walk on a
power cord. Never under any circumstance insert a cut or damaged power
cord into a mains power socket.
Power and Signal: Cables should never be connected / disconnected with
equipment powered up. Unplug mains cable before attaching or removing
signal or speaker cables Failure to heed this warning may damage or destroy
equipment and result in personal injury.
Ventilation: Electronic devices frequently run hot, but you should be able
to place your hands on them without discomfort. You must allow for this
Xs Preamp Owner’s Manual
4
heat in installation, by providing for free air circulation around the product.
The Xs Preamp is not expected to generate much heat; A 10 degree C
rise above ambient would be typical of the control chassis and the power
supply is expected to have a negligible temperature rise above ambient.
A minimum of 5 cm (2 inches) should be allowed for both side-to-side
and vertical clearance.
Electronics should not be subjected to sources of excessive radiant heat.
Excessive heat can shorten the life of the product and may cause the
electronics to self protect and shut down. Under no circumstances may the
ventilation openings be blocked with items such as newspapers, cloths or
drapes. No naked sources of ame, such as candles may be placed on or
near this product.
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 qualied service personnel.
Servicing by a qualied technician is mandatory when the apparatus has
been damaged in any way; such as when a power cord is damage, when the
device has been exposed to moisture or liquids, been dropped or does not
operate normally in any way.
For Units With Externally Accessible Fuse Receptacle: Unplug the device
from all sources of power before changing or inspecting any fuse. Replace
fuse only with one of same physical size, type and rating as that specied
by the manufacture for that product.
There is no power switch on the Xs Preamp, the unit is presumed to
operate continuously.
Safety disconnect for this product is the detachable power cord by design.
There are no internally mounted user serviceable fuses or other
components within this product. Any service issues must be refereed to a
qualied electronics service technician
Installation: It is presumed that the two Xs Preamp chassis will be stand
mounted. If installed on a cart or stand, the cart or stand must be rated by
the manufacturer to support beyond the product weight. Extreme caution
must be exercised if moving the product while installed in stand or cart to
avoid tipping and possible physical injury.
Ambient Temperatures: Normal temperature rise of this device in
extended operation is 10 degrees C. Do not operate this device in an
environment greater than 45 degrees Celsius.
Xs Preamp Owner’s Manual
5
Loading...