12
XA60 Owner’s Manual
Sometimes two designs complement each other so well that you are
surprised when you learn they weren’t invented together. So it is with
the X Supersymmetery™ amplifier and the Aleph single-ended Class A
output circuit.
The Supersymmetery™ “X” amplifier repeatedly demonstrates the pos-
sibilities for very high power, dramatic dynamic contrast, and effortless
control by a simple circuit utilizing absolutely minimal feedback. As
with the art of Aikido, the X circuit works with the intrinsic character
of a balanced circuit and deftly turns that character toward perfection.
This has been the basis for a very successful Pass Laboratories™ prod-
uct series, which has won numerous prestigious awards and garnered
critical acclaim worldwide.
For over ten years, the Aleph™ series of single-ended Class A ampli-
fiers have received praise for their outstanding sonic definition, warmth,
and smoothness; and have often been compared favorably with the very
best tube amplifiers. The Aleph™ topology achieves state-of-the-art
performance with a very simple linear design, and is additionally one of
the most stable and reliable audio amplifiers in existence.
A considerable number of audiophiles have found themselves bi-amp-
ing their loudspeakers, putting Pass Laboratories™ X amplifiers on the
bottom for power and control, conjoined with Alephs™ on the top
for that smooth warm midrange and top end. We well appreciate these
complementary differences, and for the past few years Pass Laborato-
ries™ has been at work marrying these two design concepts into a single
amplifier topology. The trick was to create an amplifier, which carries
the best of both designs, and not otherwise.
The Supersymmetry™ X amplifier uses a new radical approach to
achieving high performance from a simple 2-stage circuit. The design
exploits the symmetry of a matched balanced amplifier so that distor-
tion and noise are cancelled at the output to the loudspeaker, then uses
a small dose of a unique new form of feedback to make that symmetry
more perfect.
US Patent # 5,376,899 describes our topology, which takes advantage
of the character of specially matched balanced amplifiers that are cross-
coupled to provide cancellation of distortion and noise. The result
provides high performance with very simple linear circuits, better than
previous similar efforts by an order of magnitude. It was named Super-
symmetry™ as an homage to particle physics, but it is popularly known
as the X circuit.
Balanced amplifiers improve performance by differentially rejecting dis-
tortion and noise. To the extent that distortion and noise are identical,
XA White Paper:
Like Peanut Butter and
Chocolate
© Nelson Pass
X Supersymmetry™
