Pass Labs Amplifier, 5XA30.5 User Manual
XA30.5 Owner’s Manual
May 17, 2007
XA30.5 Owner’s Manual
Nelson Pass has been designing audio electronics since about 1971,
new company, Threshold in 1975. Threshold pioneered the design
Pass sold Threshold and created Pass Laboratories in 1991, where he
Along the way he found the time to design successful lines of
Yourself ” hobbyist community.
performance his design signature. The hardware tends to run heavy
based on the “SuperSymmetric” topology (U.S. Patent #5,376,899)
which elicits high power and performance from simple circuits with
minimal feedback.
The first X amplifier, the X1000 was intended as the premier
into 8 ohms at low distortion. By itself of course, this is no miracle,
but you have to consider that products with comparable performance
have complicated circuits with as many as nine consecutive gain
The difference was the unique balanced circuit topology in which
path.
The SuperSymmetric circuit consists of two identical matched
Most of the distortion and noise appears in phase across the
loudspeaker, and is not seen.
XA30.5 Owner’s Manual
We start with simple FET circuits already having low distortion and
noise, and arrange them in two symmetrical halves. The two halves
portion of distortion and noise without feedback. A small amount
polarities of the balanced output.
with feedback, and this is the operating principle of X amplifiers.
by the Class A “XA” amplifiers. Subsequent improvements to the
phenomenal success has led to the Class A “XA.5” series.
As always the goal has been the best musical and objective
performance possible with minimal parts in the signal path and
minimal feedback. This process is not completely understood, and
many of the improvements are the result of trial and error and
Measurement of performance is important to us, and we feel that
well-designed product sounds good and measures good. Apparently
it is possible to make an amplifier which measures well but which
X.5 and XA.5 amplifiers utilize the same basic circuit topology
AB, with an idling dissipation similar to the rated output. The XA
Within any given chassis size, the X and XA amplifiers are designed
leads to two channel amplifiers with half the output power per
half the output of Class AB amplifiers.
The X amplifiers deliver more output power per dollar, and the XA
unconditionally stable into low impedance and reactive loads.
XA30.5 Owner’s Manual
All the usual performance metrics - power, distortion, noise, input
impedance, damping factor and bandwidth have all been improved
in this latest generation. The power supplies are larger, with fast
rectifiers gating to larger capacitor banks. The increases in AC line
noise worldwide have been addressed with heavier EMI filtering
improved biasing regulation, the circuits give much more consistent
performance under varying AC line voltages and over a variety of
All this is very nice, but only if it improves your listening experience.
We listen very carefully and critically to our amplifiers with a wide
variety of associated equipment and we take our time with it.
Musical performance is most important, and is the basis of our
manufacturing decisions have to balance subjective performance
That is why we make more than one amplifier, but all are built with
www.passlabs.com
Tel (530) 367 3690
Pass Labs,
PO Box 219
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