| The Aleph P is a stereo line level selector and variable gain stage
featuring balanced single-ended Class A circuitry. It offers four pairs of input channels
configured as balanced or unbalanced, and two pairs of balanced or unbalanced outputs.
Controls consist of an input selector, gain adjustment for left and right channels, and
master gain control. The Aleph P also offers remote control of the input select and master
gain. The central element of the Aleph P is a new, patented, and incredibly simple
single-ended gain stage where each input line is amplified by a single power Mosfet.
Operated in single-ended Class A mode, the Mosfet's control gate is connected directly to
the input signal, and the output is taken from the drain.
This simplicity results in sonic purity. In other products, the signal passes through
many gain stages, each adding its own noise and coloration, justified by additional
feedback gain they provide. The Aleph P delivers very high quality measured and subjective
performance without the use of complex circuitry.
The circuitry of the Aleph P handles balanced and unbalanced signals in a natural and
flexible manner. The gain stages accept balanced or unbalanced input signals, delivering
balanced outputs with either. Unbalanced output is obtained by simply connecting only the
+ output line. Balanced connections are achieved through XLR connectors, and unbalanced
connections are furnished through RCA connectors.
The differential output of the circuit is an accurate reflection of the differential
input, whether signal is presented to both inputs (balanced) or only one input
(unbalanced). Matching of the gain devices and related components keeps variations within
1% total, giving a common mode rejection figure of 60 dB. A single-ended input connection
will result in both unbalanced and balanced outputs to drive a power amplifier.
The gain stages for each line are operated single-ended Class A. The virtues of such a
topology are discussed at length elsewhere in our literature, but we believe that the
single-ended characteristic is the most topologically simple and musically natural way to
amplify audio. Ordinarily there is a conflict between balanced lines and a single-ended
characteristic. If two identical single-ended gain stages are used to amplify differential
signal, their differential output reflects the distortion typical of a push-pull circuit.
It will have lower distortion, but the second harmonic content is suppressed.
The Aleph P circuitry is designed to retain the single-ended characteristic for
single-ended inputs, and the balanced characteristic for balanced inputs. The transfer
curve and distortion for single-ended (unbalanced) inputs is asymmetric and second
harmonic, without regard for whether you use the balanced or single-ended outputs on the
preamp. As a result, a single-ended characteristic is retained for both balanced and
unbalanced connections to power amplifiers. At the same time, the circuit retains the
balanced characteristic for inputs using the XLR connection. This occurs naturally in the
circuit, without switching or adjustment, dependent only on the nature of the input
signal.
The master level control for all four output lines is accomplished with sixteen
microprocessor controlled double-pole-double-throw relays and precision metal film
resistors. The level control is placed at the output of the gain circuitry before the
output of the preamp, and serves to attenuate preamp noise as well as signal. The front
panel selector and volume control are controlled by optical encoders or by the infra-red
remote.
The impedance of the master level control is low, so that the output impedance of the
preamp ranges from 0 ohms to a maximum of 800 ohms, depending on the setting. Typical the
output impedance is 100 ohms, and the preamp will meet full bandwidth specifications into
long cable runs and low impedance loads.
Because it operates without feedback and is buffered by the passive output attenuator,
the preamp does not suffer distortion due to loading. The output of the preamp will drive
any impedance load without distortion to 20 ma peak, or greater than +20 dBm into 600
ohms.
The Aleph P chassis and its remote control are machined out of solid aluminum. No sheet
metal is employed in its construction. The aluminum is brushed and anodized at the finest
finishing house on the West coast, and is laser engraved.
Aleph P is designed to maximize the performance of single gain devices operated in
single-ended Class A mode. The objective measurements indicate superlative performance,
but do not hint at the warmth, detail, and ambiance of the sound of the preamplifier.
Because the signal need only pass through a single Mosfet, there is a tremendous intimacy
between the input and output, and very little loss of information. The inherent simplicity
of the gain path gives the best possible performance, second only to no gain stage at all.
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