Pass Labs X250.5

X250.5 Owners Manual

The Pass Laboratories ™ X250.5 stereo amplifier embodies the de-

sign technolog y 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 X250.5 to significantly improve this products sonic

perfor mance in comparison to it’s immediate predecessor, the Pass

Laboratories™ X250.

The Supersymmetr y™ circuit topolog y was g ranted a U.S. patent in

1994, and was the result of 19 years of effor t by legendar y analog

designer and company founder Nelson Pass. The amplifier uses

highly matched components in a classically simple single ended Class

A circuit. T he amplifier contains only two simple stages: the first is a

balanced Class A g ain stag e. Its output drives a bank of high power

devices operated as followers.

These are inherently low distor tion 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 Supersymmetr y™ enhances this effect by provid-

ing a connection between the two halves of the balanced circuit that

further perfects the match of common mode ar tifacts. Any distor-

tion and noise not already identical to the two halves is made more

identical by a factor of about 10. T he 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 distor ted signal, Supersymme-

tr y™ seeks merely to create perfect matching between the two halves

of an otherwise well matched circuit.

Matched balanced power circuitr y typically sees a distor tion and noise

reduction of about 90% (20 dB) through a balanced connection

without any additional effort. The Supersymmetr y™ 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. Distor tion and noise can still be seen at the output of one half of

the circuit, but since it is vir tually identical on the other half, these un-

desirable ar tifacts larg ely g o away at the speaker ter minals. This gives

g ood measured perfor mance, and because a simple circuit produces it,

also sounds quiet excellent.

Introduction