| 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 output swing, variable cartridge loading, variable gain, and balanced output. The
Aleph Ono uses three stages of circuitry. An ultra- low noise non-inverting
pre-preamplifier 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
un-equalized 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 for cartridges with 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 pre- preamplifier 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. |
