Pass Labs PASS X250.5 User Manual

pass

TM

May 17, 2006

X250.5 Owners Manual

X250.5 Owner’s Manual

1

Introduction

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

performance in comparison to it’s immediate predecessor, the Pass

Laboratories™ X250.

The Supersymmetry™ circuit topology was granted a U.S. patent in

1994, and was the result of 19 years of effort 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 gain stage. 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 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. 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 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 effor t. 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. 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.

X250.5 Owners Manual

2

Previously these kinds of simple Class A circuits have been popular

for their sound quality in low power amplifiers, but have not found

application at high power levels due to excessive distortion and low

efficiency. Supersymmetr y™ overcomes this barrier, delivering the

sweetness, staging, and detail of very simple circuitry up to kilowatt

power levels and beyond.

The X.5 Series amplifiers have the tremendous dynamic rang e (>140

dB) to do justice to the high-resolution digital recordings of the 21st

Century and the elegance to retrieve the micro dynamics offered by

the most sensitive loudspeakers. The simple but powerful circuitry

moves easily from total silence to explosive transient and back to

silence without a trace and without information loss. Very unlike

conventional high power amplifiers, they provide this level of power

with a subtlety befitting some of the better tube amplifiers. This per-

formance is consistence across the audio spectrum and the amplifiers

are unconditionally stable into all speaker loads.

So relax and enjoy your amplifier. Call us if you ever have a problem

or question. You are welcome to ask questions or offer comments.

Thank you for buying our product.

X250.5 Owners Manual

3

Setup

You can position this amplifier most anywhere you wish, but it re-

quires adequate ventilation. We do not recommend placing it in

enclosed cabinets or small closets without means for air to circulate

freely. Stacking these power amplifiers directly upon each other is not

recommended for the same reason. This amplifier typically idles at

slightly less than 350 watts, most of which dissipates as heat across

the heatsinks. As a point of reference, these heatsinks should never

become too hot to touch for several seconds.

Let’s talk about AC power requirements. This amplifier draws about

3 amps (continuous rms) at 120 volts out of the wall during normal

operation, and this power draw ref lects mostly the idle current that

we run through the output stage. If you are driving a low impedance

load, you will draw more power than this, but this will not be typical.

The amplifier’s voltage and current rating are indicated on the rear

panel. It will be 240 volts, 220 volts, 120 volts or 100 volts, all with

an appropriate rear mounted resetable circuit breaker. The frequency

rating of the AC line source in all instances will be 50 to 60 Hz. Please

verify that the amplifiers indicated voltage requirements are consistent

with the line voltage supplied at your location.

The Pass Laboratories™ X250.5 is provided with a conventional IEC

detachable AC line cord, which is rated at 15 amps. The safety ground

is attached to the chassis in the conventional approved manner. The

AC power input to the amplifier runs through a RF filter, which re-

moves high frequency noise coming into and going out of the ampli-

fier power supply.

Under no circumstances should you defeat the ground connection of

the power cord. For your safety, the chassis of the amplifier should be

earth grounded. Signal ground is isolated from chassis, safety ground,

to reduce the incidence of ground loop noise. The presence of a

safety ground will not degrade the audio signal chain.

You may substitute an aftermarket detachable IEC 320 style power cord

of your choosing; provided it is rated for at least 15 amps and it meets all

legal requirements and has been approved by the local testing authority

for such things.

Looking at the rear panel you will see the IEC 320 AC power cord

receptacle, a thermal magnetic breaker switch, two pairs of output con-

nectors, a pair of binding post connectors for remote turn-on, one RCA

input connector and one XLR balanced input connector.

X250.5 Owners Manual

Make sure that the breaker switch is off (down). Plug the AC cord into

4