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13

XA60 Owner’s Manual

they vanish at the output, typically by a factor of 10 or so for matched 

single-ended Class A circuits.  

Supersymmetry™ extends this concept by using feedback only to make 

the distortion and noise more identical on each half of a balanced cir-

cuit, not to eliminate it as such.  This gives as much as a 100:1 reduc-

tion in unwanted distortion and noise without requiring the equivalent 

amount of negative feedback.  It is simply much easier to tweak the two 

halves of the circuit into identical symmetry than to eliminate all the 

distortion in each half of the circuit.

The result has been a successful series of high power amplifiers offering 

low distortion, and stunning dynamic range and control, with only two 

gain stages and very minimal feedback.  

Supersymmetry™  is  ideally  used  to  obtain  high  quality  performance 

from very simple gain circuits, and particularly favors single-ended Class 

A topologies due to their smooth second harmonic characteristic, which 

cancels easily.  

Single-ended Class A has long been known as the “King of the Class 

A’s”, the simplest, most pure and least efficient form of audio amplifi-

cation.  Before the Aleph™ amplifiers, it was reserved for preamplifier 

circuits,  high  quality  amplifier  front-ends,  and  other  very  low  power 

output stages.

US Patent # 5,710,522 describes the single-ended Class A power ampli-

fier biased by a constant DC current source which negatively “ghosts” 

the speaker load with simple but effective current modulation.  If you 

have followed developments in audio for the last 10 years, you know this 

design as the Pass Laboratories Aleph™.  The Aleph™ is an incredibly 

successful ground breaking amplifier design, hailed in Stereophile maga-

zine as “The Amplifier of the Decade” and winner of virtually every 

international design award for audio that we know of.

The key virtue of the Aleph™ design lies in its simplicity and effective-

ness.  With only two stages and no adjustments it delivers measured 

performance rivaling the most complex designs, but retains the sonic 

elegance and nuance of a truly minimalist gain path – only two gain 

devices in series from input to output.

The two design concepts are not mutually exclusive, and we approached 

the development of the XA series with an eye to creating a warm/sweet 

X amplifier, or conversely, a powerfully dynamic Aleph™.  The success-

ful result is a circuit which is described as balanced single-ended Class 

A, consisting of two balanced Aleph™ amplifiers sharing a single dif-

ferential input pair of transistors.  

Aleph Single-Ended Class A

 

The Supersymmetery 

Aleph™

Summary of Contents for XA60

Page 1: ...1 XA60 Owner s Manual pass TM XA60 Owner s Manual May 18 2006 ...

Page 2: ...rcuit topology that we descriptively characterize as being Single ended Class A This new topology combines the very best characteristics of Pass Laboratories X series amplifiers and the highly rated Pass Laboratories Aleph The XA series is the marriage of a highly refined Aleph output stage with the patented Supersymmetry X front end The emphasis of the XA series is to accentuate performance and s...

Page 3: ...le into any load presented by a loudspeaker but will provide less power into other than 8 ohms The XA60 accommodates both single ended RCA and balanced inputs XLR Input impedance s are 11 kohm unbalanced and 22 kohm balanced to permit integration with the widest possible range of upstream components You can position this amplifier anywhere you wish but it must have ventilation We do not recommend ...

Page 4: ...ar panel It will be either 240 volts 220 volts 120 volts or 100 volts all units protected by a type 3 AG slow blow fuse of the appropriate ampacity The operational voltage is not user changeable Transformers are input voltage specific and their change is not a trivial matter The frequency rating of the AC line source is 50 to 60 Hz in all cases Please verify that the amplifiers indicated voltage r...

Page 5: ...se Some powered subwoofers require an audio signal ground reference and their makers may suggest that a black speaker terminal is where this voltage reference might be found On complementary designs which would be typical of all power amps produced by Pass Laboratories this is an incorrect and unsafe assumption On all Pass Laboratories power amplifiers a reference of 0 volts will be found only at ...

Page 6: ...product is very low This is small comfort to the few but take it easy and give us a call if you have problems People are interested in how long it takes for these amplifiers to break in Depending on the resolution of the rest of your audio chain you may or may not notice any break in of the XA60 beyond the first 50 hours of operation You will likely notice the difference in sonic character between...

Page 7: ...lightly less distortion at a given voltage current level than resistive loads The XA circuit was designed to be quite happy driving electrostatic speakers and any other esoteric loads we know of We have a general recommendation about interconnects and speaker cables which is that they should cost less than the amplifier and contain at least some conductive material We have tried a lot of products ...

Page 8: ...supply filter capacitors These caps are used to create the unregulated output stage rails RC filtering is used to passively remove ripple from the supply rails All the power transistors in the product are hyper matched parts with gate voltages matched to 0 5 and all devices taken from the same manufacturing lot codes made on the same wafer So how long will this hardware last It is our experience t...

Page 9: ...l Slew rate plus minus 50 V uS Output Noise 300 uV unweighted 20 20 kHz Balanced CMRR approx 60 dB 1 kHz DC offset 100 mv Power Consumption approx 300 watts Temperature 25 degrees C above ambient at idle Dimensions 19 W x 7 H x 20 D Shipping Weight 68 lbs For more information please contact Pass Laboratories Inc P O Box 219 24449 Foresthill Rd Foresthill CA 95631 Tel 530 367 3690 Fax 530 369 2193 ...

Page 10: ... of origin for warrantee service Foreign distributors are only required to offer warranty service on Pass Laboratories product that they have imported Please note Conditions of warranty service and customer rights for product purchased outside the United States may vary depending upon the distribu tor and local laws Please check with your local distributor for specific rights and details Any modif...

Page 11: ... one that is fully safety rated by the necessary local authority Power Cord Protection Power supply cords should be routed so that they are not likely to be walked on abraded or pinched by items placed on or against them paying particular attention to cords where they enter plugs or exit from a device Never under any circumstance insert a cut or damaged power cord into a mains power socket Power a...

Page 12: ...speakers 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...

Page 13: ...d for preamplifier circuits high quality amplifier front ends and other very low power output stages US Patent 5 710 522 describes the single ended Class A power ampli fier biased by a constant DC current source which negatively ghosts the speaker load with simple but effective current modulation If you have followed developments in audio for the last 10 years you know this design as the Pass Labo...

Page 14: ...ve ambient temperature so that actual chip temperatures are about 70 degrees below their rating The output devices are designed to last a very long time under these conditions with a probable life of about 50 000 hours The power supply of the XA 200 uses elaborate RF filtering and noise sup pression designed to block AC noise and line DC The substantial toroidal power transformer is followed by hi...

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