Pass Labs XA100 - Manual (Page 14)

14 XA100 Owner’s Manual
The amplifier has only the two stages, an input stage of a balanced pair of
input devices, and the output stage, a balanced pair of single-ended Class
A power Mosfets. Like the Aleph™, you can trace a path from input to
output through only two gain devices. Like the X amps, feedback is used
only to set the gain and correct for dissimilarities between the two matched
output stages.
There are no adjustments. There are no frequency compensation capaci-
tors. The amplifiers are unconditionally stable and reliable into any load.
They are not fragile, temperamental or prone to failure.
The XA amplifiers operate at approximately 33% efficiency, which is to
say they idle at three times their rated output. The XA200 is rated at 200
watts output into 8 ohms and draws something over 600 watts of AC
power. This design is an exercise in highly conservative engineering, which
provides exceptional reliability and product longevity. The output devices
are exposed to no more than a fraction of the voltage and wattage they are
designed to endure.
These rugged power devices are matched to about .3% and mounted on
Mica insulators. Their massive heat sinks run at about 25 degrees C. above
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 high speed rectifiers, and significant uF
of computer grade capacitors in a passive filter arrangement. In addition
to a main power switch the amplifier has a standby mode, which shuts
down the bias to the circuit while keeping the supply active, significantly
extending the life of the filter capacitors.
The sound of the XA amplifiers is a quantum leap over the parents. They
retain the sweet warmth and lushness of the Aleph™ series without the
fluffy coloration’s. The dynamic contrast is even better than the X series;
transients leaping from black to crescendo and back again with no tele-
graphing or hangover.
The bass has as much control over the speaker as the original X amps, but
is a bit more neutral and carries subtler nuance. The midrange is a little
deeper and the soundstage wider than the Alephs™.
Are the XA’s better than Alephs™ and X’s in every respect?
Yes, except for the higher power/current ratings of the X amps.
Are they the best audio amplifiers that money can buy? Absolutely!