2
X
s
Preamp Owner’s Manual
Introduction
There are people who do not know that Wayne Colburn has
designed the Pass Labs preamplifier 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 pre-
amplifiers and phono stages, each recognized as offering a genuine
improvement in sound quality.
When we began development of the Xs power amplifier five 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 amplifier 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 fits 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 amplifiers 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 figure of the volume control has been tweaked
to favor 2
nd
harmonic over 3
rd
. 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,
