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X600.5 Owners Manual
The Pass Laboratories ™ X600.5 stereo amplifier embodies the de-
sign technology and refinements of the “X” series amplifiers includ-
ing extensions of the patented Supersymmetry™ circuit. Additionally
selected refinements of the XA series amplifiers have been incorpo-
rated into the X600.5 to significantly improve this products sonic
performance in comparison to it’s immediate predecessor, the Pass
Laboratories™ X600.
The Supersymmetry™ circuit topology was granted a U.S. patent in
1994, and was the result of 19 years of effort by legendary analog
designer and company founder Nelson Pass. The amplifier uses
highly matched components in a classically simple single ended Class
A circuit. The amplifier contains only two simple stages: the first is a
balanced Class A gain stage. Its output drives a bank of high power
devices operated as followers.
These are inherently low distortion types of circuits, but their perfor-
mance is significantly improved when operated as balanced devices.
Distortion and noise identical to both halves of a balanced circuit can
be made to disappear at the output, and in a well-matched symmetric
circuit, most of the distortion and noise is identical.
Pass Laboratories Supersymmetry™ enhances this effect by provid-
ing a connection between the two halves of the balanced circuit that
further perfects the match of common mode artifacts. Any distor-
tion and noise not already identical to the two halves is made more
identical by a factor of about 10. The result of this perfected match
is improved noise cancellation at the output of the amplifier. From a
listeners standpoint this results in a more accurate presentation of the
soundstage and better resolution of low level detail.
Unlike feedback techniques where the goal is to correct for the distor-
tion by feeding a gain stage an inversely distorted signal, Supersymme-
try™ seeks merely to create perfect matching between the two halves
of an otherwise well matched circuit.
Matched balanced power circuitry typically sees a distortion and noise
reduction of about 90% (20 dB) through a balanced connection
without any additional effort. The Supersymmetry™ circuit delivers
another 90% reduction, so that the X series has about 1/100 of the
distortion of a conventionally simple and otherwise identical ampli-
fier. Distortion and noise can still be seen at the output of one half of
the circuit, but since it is virtually identical on the other half, these un-
desirable artifacts largely go away at the speaker terminals. This gives
good measured performance, and because a simple circuit produces it,
also sounds quiet excellent.
Introduction
