Dear Customer,
The Pass Aleph 60 is the part of the second generation of Aleph single-ended Class A power
amplifiers. This design results from my commitment to create the best sounding product, a
simple circuit having the most natural characteristic. The Pass Aleph 60 integrates power
Mosfet devices and pure single ended Class A operation in a simple two-gain-stage topology
with the sole purpose of recreating subjectively natural sound.
The Pass Aleph 60 is unique in a number of ways:
Most amplifiers on the market have between five and seven gain stages in series between the
input and the output. The Aleph 60 has but two, and enjoys a very direct path from input to
output, further enhancing the purity of the circuit and the resulting sound.
The output stage of the Aleph 60 is a unique blend of traditional design and innovation
addressing the unique requirements of loudspeakers. Previous methods of loading the output
stage have used networks consisting of resistors, coils, transformers, and active current
sources, all of which offer an optimal load line based on a resistive load. The Aleph 60 has a
current source topology which optimizes performance for a wide range of impedance and
reactance in the load, improving all aspects of performance into real loudspeakers. Pass
Labs has US patent No. 5710522 on this output stage topology.
The Aleph 60 is unique in that there are no adjustments of any kind in the circuitry. There are
no potentiometers to adjust. The operating parameters of bias currents and DC offset and so
on are defined by physical constants, and will not go out of adjustment.
Most important, the Aleph 60 brings improvement to the recreation of subjective sonic reality.
The amplifier delivers detail and subjective space rarely found in semiconductor circuits,
coupled with the authority and clarity rarely found in tube amplifiers.
The Pass Aleph 60’s ancestry lies in the highly praised Aleph 2. We have kept virtually all of
the circuit design and choice of parts intact, and the output wattage rating has been adjusted
to the smaller heat sinks.
The balanced input circuitry is the same topology as the rest of the original Aleph series,
accomplishing true high performance balanced input without additional active components. It
has been improved, however, to offer a higher input impedance on the single-ended input, 47
Kohms. The original Aleph 2 had a 10 Kohm input impedance.
The input devices are the same as the originals, but significant improvement is to be found in
the manner of matching the input devices. Previously the input differential transistors were
merely matched to each other, but beginning with the Aleph 30 and 60 they are now matched
both to each other and to the rest of the amplifier circuit. We select the input devices as part
of the complete amplifier, swapping them in and out until the best performance is achieved.
Tweaking the input stage in this manner and with other adjustment techniques we have been
able to significantly lower the noise floor and improve the power supply noise rejection of the
amplifier.
