PassLabs Aleph 0 Owners manual

Pass Laboratories

Aleph 0 Owner's Manual

Introduction

The Aleph 0 is a single ended Class A audio power amplifier, the first product produced by
Pass Laboratories. It combines completely new design thought applied to a traditional
topology and the experience of twenty five years of amplifier design.

This power amplifier flows from a commitment to create the best sounding product: a simple
circuit with the most natural characteristic. The Aleph 0 integrates power Mosfet devices and
single ended Class A operation in a simple topology in order to deliver natural sound, the
reference for naturalness being taken as the acoustic characteristic of air.

Consuming four times the rated output power, single ended Class A makes ordinary push-pull
circuits appear comparatively efficient. This inefficiency has been a deterrent to designers,
limiting this "king" of Class A circuits to preamps and input stages.

I feel that in specialized and demanding applications, the energy penalty is worth the purity of
performance obtainable from single ended Class A operation. This purity delivers the most
musicality and listening satisfaction per watt of any operating mode.

Over the years I have remained fascinated by the characteristic sound of the single ended
topology, but until now I did not have the opportunity to bring such a product to market.

A very few people are involved in the production of this product. I supervise all phases of the
construction, and I test and listen to each amplifier myself. If you have questions, comments,
or problems, please feel free to contact me directly.

Thank you for purchasing this amplifier. It is my sincere hope that you will enjoy its sound as
much as I do.

_________________________________
Nelson Pass

Serial # ____________________

Date: ____________________

Next page: Distortion curve of your particular amplifier into 8 ohm versus output watts.

Setup

The amplifier has three sets of connections and one switch: The first connection and switch is
the AC line power system. The amplifier's voltage and current rating are indicated on the
bottom. It will be either 240 volts, 120 volts, or 100 volts, all with a 6 amp 3AG type fuse. The
frequency rating of the AC line source is 50 to 60 Hz.

Your amplifier is provided with a standard AC power cord which fits into the line receptacle
located just below the power switch. The amplifier is equipped for operation with an earth
ground provided by the AC outlet. Do not defeat this ground. The chassis of the amplifier is
connected directly to this earth ground, and the audio circuit ground is connected to the
chassis and earth through a power thermistor, which gives a ground safety connection but
helps avoid ground loops. While the amplifier is equipped with an AC inrush suppresser, the
turn-on AC draw will peak (half cycle) at roughly 50 amps on a 120 volt system and 25 amps
on a 240 volt system. The fuse on the amplifier is a 3AG fast blow type rated at 6 amps. It is
in series with the AC power line.

The second connection is at the input. If your signal source is balanced, you may use the
XLR input connector. On this connector, pin 1 is grounded, pin 2 is the positive signal input,
and pin 3 is the negative signal input. To run balanced input, remove the copper shorting
jumper between pins 1 and 3 on the XLR connector. Save the jumper.

If your signal source is unbalanced, input will occur through the RCA input. In unbalanced
use, the copper shorting jumper can be used between pins 1 and 3 on the XLR which
terminates the pin 3 negative input to ground. When running unbalanced input, use of this
plug will increase the amplifier’s gain to 26 dB in the event that you need or prefer higher gain
than the standard 20 dB figure. If you don’t need that extra gain, our own preference is to not
use the shorting plug.

If you insert the copper shorting jumper, and the amplifier stops operating, you will find that it
is not in pins 1 and 3.

The unbalanced input impedance of the amplifier is a nominal 10 Kohm. In balanced mode,
the input impedance is higher, with a differential impedance of about 25 Kohm. Common
mode input impedance is matched at 20 Kohm per input.

The third connection is the amplifier output connection. Connect the 5-way output connectors
to loudspeaker plus and ground, using the cable of your choice. Do not drive the amplifier
into a direct short. If distortion or fuse blowing accompany an attempt to operate the amplifier,
please disconnect the loudspeaker first and check for a shorted circuit. As the amplifier does
not use a current limiting protection circuit, quite a large amount of power can flow from the
amplifier, and might damage the output stage.

At rated power, the amplifier draws approximately 300 watts from the wall, and during idle
operation most of this energy will appear as heat on the heat sinks. Good ventilation is vital to
the proper operation of the amplifier. It has been adjusted for optimal performance at room
temperature, but will work well between 50 and 90 degrees Fahrenheit (10 to 33 Celsius).
You should leave at least six inches clearance on the sides and top. The amplifier should not
be placed in a closed cabinet which does not have forced air ventilation.

This amplifier runs hot. The heat sinks will warm up in about an hour to a temperature which
will not be comfortable to touch for more than a moment or two, which is 120 to 130 degrees
Fahrenheit (50 to 55 degrees Celsius). This is normal, and there is a thermal shut off system
which will shut down the amplifier at internal temperatures in excess of 160 deg. F. and 70
deg. C. If the over temperature protection system is activated, it will shut down the amplifier
until the thermal sensor has cooled.

It takes at least an hour of warm up time to get the best performance out of the amplifier. It
will take that long to reach operating temperature and exhibit lowest DC offset voltage at the
output. However, prior to warm up, the amplifier will meet objective performance
specifications except DC offset voltage.

The amplifier does not require any maintenance. While the design is conservative, this is a
hard running amplifier, as single ended Class A operation is the least efficient operating
mode. In fifteen years the electrolytic power supply capacitors will get old. Depending on
usage, you will begin to have semiconductor and other failures between 10 and 50 years after
date of manufacture. Later, the sun will cool to a white dwarf, and after that the universe will
experience heat death.

Product Philosophy and Design Theory

When I started designing amplifiers 25 years ago, solid state amplifiers had just achieved a
firm grasp on the market. Power and harmonic distortion numbers were king, and the largest
audio magazine said that amplifiers with the same specs sounded the same.

We have heard Triodes, Pentodes, Bipolar, VFET, Mosfet, TFET valves, IGBT, Hybrids, THD
distortion, IM distortion, TIM distortion, phase distortion, quantization, feedback, nested
feedback, no feedback, feed forward, Stasis, harmonic time alignment, high slew, Class AB,
Class A, Pure Class A, Class AA, Class A/AB, Class D, Class H, Constant bias, dynamic bias,
optical bias, Real Life Bias, Sustained Plateau Bias, big supplies, smart supplies, regulated
supplies, separate supplies, switching supplies, dynamic headroom, high current, balanced
inputs and balanced outputs.

Apart from digitally recorded source material, things have not changed very much in twenty
five years. Solid state amplifiers still dominate the market, the largest audio magazine still
doesn't hear the difference, and many audiophiles are still hanging on to their tubes. Leaving
aside the examples of marketing hype, we have a large number of attempts to improve the
sound of amplifiers, each attempting to address a hypothesized flaw in the performance.
Audiophiles have voted on the various designs with their pocketbooks, and products go down
in history as classics or are forgotten. The used market speaks eloquently: Marantz 9's
command a high price, while Dyna 120's are largely unwanted.

There has been a failure in the attempt to use specifications to characterize the subtleties of
sonic performance. Amplifiers with similar measurements are not equal, and products with
higher power, wider bandwidth, and lower distortion do not necessarily sound better.
Historically, that amplifier offering the most power, or the lowest IM distortion, or the lowest
THD, or the highest slew rate, or the lowest noise, has not become a classic or even been
more than a modest success.