Pass Laboratories
Aleph 0s Owner's Manual
Introduction
The Aleph 0s is a single ended Class A audio power amplifier sharing the same basic design as the Pass Labs Aleph 0, except that the hardware resources of the Aleph 0 are split between two channels to form a stereo amplifier rated at 40 watts per channel.
This power amplifier design flows from a commitment to create the best sounding product: a simple circuit with the most natural characteristic. The Aleph 0s 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, or Asymmetric 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 . The Aleph 0s is the second product to come from Pass Laboratories reflecting this design vision.
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 ohms 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 panel. It will be either 240 volt with a 6 amp fuse, a 120 volt with a 6 amp fuse, or a 100 volt with a 6 amp fuse. The frequency rating of the AC line source is 50 to 60 Hz. On the rear panel is an AC line power switch used to turn the amplifier on and off. A blue Led lamp mounted in the front panel indicates power.
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 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, which is a standard female XLR connector. It is configured for balanced input, and if you wish to run the amplifier from an unbalanced source, you may configure it for unbalanced source using an adapter as described later in this manual. On this connector, pin 1 is grounded, pin 2 is the positive signal input, and pin 3 is the negative signal input. In balanced mode, the input impedance is nominally 25 Kohm, and the unbalanced input impedance of the amplifier is nominally 10 Kohm.
The amplifier is shipped with a shorting plug between pins 1 and 3 of the XLR input connector. Remove this plug and save it if you are using a balanced connection to the source. If you are using an RCA connection to the source, you may operated the amplifier with or without this shorting plug. Use of the shorting plug will give 26 dB of gain, and without will give 20 dB of gain. You may operate it either way as you prefer.
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. The polarity of the red output connectors is +, and the black connectors are ground. Although they are at ground, It is not recommended that you attach the black output connectors to anything other than the loudspeaker terminals.
The amplifier will drive any known loudspeaker load which dips as low as 2 ohms. 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. The design has been tested to survive external short circuits, but the possibility exists for failure under these conditions. Such failure is covered by your warranty.
At rated power, the amplifier draws approximately 250 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 particularly comfortable to touch, 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 75 deg. C. If the over temperature protection system is activated, it will shut down the amplifier until the thermal sensor has cooled. If you find that the amplifier has shut down, turn it off and investigate the cause before attempting to use it further.
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 measurable 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, 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.
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