PassLabs Aleph Ono Owners manual

Pass Laboratories

Aleph Ono Owner's Manual

Introduction

The Aleph Ono is a high performance phono preamplifier for use with moving magnet and
moving coil cartridges. It features extremely low noise and distortion, very high gain and
output swing, variable cartridge loading, variable gain, and balanced output.

The Aleph Ono uses three stages of circuitry. An ultra-low noise non-inverting pre­preamplifier circuit is used to boost the low output of moving coil (MC) cartridges by a
selectable 25 or 30 dB without equalization. This drives the primary non-inverting gain stage
which also amplifies the high output of moving magnet (MM) cartridges, and provides RIAA
equalization. Output of the primary gain stage is also applied to an inverting unity gain stage
to provide the negative polarity for the balanced output.

The main gain stage uses low noise matched JFETs for the input circuit and power
MOSFETs elsewhere in the gain path. Voltage gain devices are operated cascode mode,
and the single-ended circuitry is biased by constant current sources.

The main gain stage uses a combination of active and passive equalization to achieve the
RIAA characteristic. The active equalization works in the mid-band of the audio range and
the passive equalization determines the characteristic and the highest and lowest
frequencies. The stage has a fixed gain value of 40 dB at 1 KHz.

The pre-preamplifier circuit uses four matched ultra-low noise JFETs operated in parallel to
provide an input random noise floor less than 500 picovolts (-186 dBV). The cascoded
output of these JFETs drives another JFET to deliver a selectable 25 or 30 dB of un­equalized non-inverting gain. There is no feedback employed.

Cartridge loading of the Aleph Ono is very flexible. Moving Magnet cartridges can be loaded
with capacitance from 0 to 650 pF in increments of about 100 pF. There is provision for two
load positions for any additional value the user may choose to insert. Moving Coil cartridge
loading ranges from 5 to 1000 ohms to 47 Kohms using eight switches with binary weighting
and providing 256 different values.

The balanced and unbalanced output connections of the preamplifier have an output
impedance of 150 ohms, which will drive a 1000 pF cable load flat to about 1 megahertz.

The Aleph Ono has a very accurate RIAA equalization characteristic, varying plus or minus
1/10 of a decibel from 20 to 20 KHz. This accuracy does not vary with gain or loading.

The preamplifier has extremely low noise. The curves accompanying show a Moving
Magnet noise floor at more than -100 dB below a 10 millivolt input, which gives it an
unweighted total noise of -90 dB. The Moving Coil noise floor is better than -90 dB
referenced to 1 millivolt input, giving a -81 dB unweighted audio band noise figure.

The Aleph Ono is adjustable to very high gain, 76 dB @ 1 KHz, which makes it capable of
delivering .5 V line level output with cartridges 80 microvolts output. This appears to be the
best figure in the audio industry.

The preamplifier has very low distortion and very high output. Maximum harmonic distortion
is less than .05% (1 KHz) at outputs of 20 volts RMS. or less. This figure holds for MM
operation and highest gain MC.

The power supply of the Aleph Ono uses a shielded oversize toroidal transformer providing
an unregulated 80 volts DC which is then passively RC filtered, then actively regulated
without feedback to 60 volts, and then passively filtered again for each channel. The pre­preamplifier circuitry is additionally regulated.

The Aleph Ono was engineered through listening tests over a period of two years in
competition with the most highly regarded phono stages on the market. Changes in the
design were based solely on listening experience, and not on measurements.

Considering this, it is perhaps remarkable that the final product displays such spectacular
objective qualities. However, we view the specifications as a secondary source of pride in
this product.

The measurements only hint at the listening experience with the Aleph Ono. The sound is
lush and smooth, with a wide sound stage, fine detail and layering, and a nice firm bottom.
The preamplifier will allow you to renew your acquaintance with your vinyl collection and
appreciate the essential character of the finest analog recordings.

The Aleph Ono is the work of Wayne Colburn. He supervises its construction, and personally
tests and listens to each preamplifier. If you have questions, comments, or problems, please
feel free to contact him or me directly.

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

_________________________________
Nelson Pass

Serial # ____________________

Date: ____________________

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