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For a long time there has been faith in the technical community that eventually some objective
analysis would reconcile critical listener's subjective experience with laboratory measurement.
Perhaps this will occur, but in the meantime, audiophiles largely reject bench specifications as
an indicator of audio quality.  This is appropriate.  Appreciation of audio is a completely
subjective human experience.  We should no more let numbers define audio quality than we
would let chemical analysis be the arbiter of fine wines.   Measurements can provide a
measure of insight, but are no substitute for human judgment.

As in art, classic audio components are the results of individual efforts and reflect a coherent
underlying philosophy.  They make a subjective and an objective statement of quality which is
meant to be appreciated.  It is essential that the circuitry of an audio component reflects a
philosophy which address the subjective nature of its performance first and foremost.

Lacking an ability to completely characterize performance in an objective manner, we should
take a step back from the resulting waveform and take into account the process by which it
has been achieved.  The history of what has been done to the music is important and must be
considered a part of the result. Everything that has been done to the signal is embedded in it,
however subtly.

Experience correlating what sounds good to knowledge of component design yields some
general guidelines as to what will sound good and what will not:

1)  Simplicity and a minimum number of components is a key element, and is well reflected in
the quality of tube designs.  The fewer pieces in series with the signal path, the better.  This
often true even if adding just one more gain stage will improve the measured specs.

2)  The characteristic of gain devices and their specific use is important.  Individual variations
in performance between like devices is important, as are differences in topological usage.  All
signal bearing devices contribute to the degradation, but there are some different
characteristics are worth attention.  Low order nonlinearities are largely additive in quality,
bringing false warmth and coloration, while abrupt high order nonlinearities are additive and
subtractive, adding harshness while losing information.

3)  Maximum intrinsic linearity is desired.  This is the performance of the gain stages before
feedback is applied.  Experience suggests that feedback is a subtractive process; it removes
information from the signal.  In many older designs, poor intrinsic linearity has been corrected
out by large application of feedback, resulting in loss of warmth, space, and detail.

High idle current, or bias, is very desirable as a means of maximizing linearity, and gives an
effect which is not only easily measured, but easily demonstrated:  Take a Class A or other
high bias amplifier and compare the sound with full bias and with bias reduced.  (Bias
adjustment is easily accomplished, as virtually every amplifier has a bias adjustment pot, but it
should be done very carefully).  As an experiment it has the virtue of only changing the bias
and the expectations of the experimenter.

 As the bias is reduced the perception of stage depth and ambiance will generally decrease.
This perception of depth is influenced by the raw quantity of bias current.
If you continue to increase the bias current far beyond the operating point, it appears that
improvements are made with bias currents which are much greater than the signal level.

Summary of Contents for Aleph 0

Page 1: ...Pass Laboratories Aleph 0 Owner s Manual ...

Page 2: ... 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 b...

Page 3: ...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 ...

Page 4: ... 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 ...

Page 5: ...s in series with the signal path the better This often true even if adding just one more gain stage will improve the measured specs 2 The characteristic of gain devices and their specific use is important Individual variations in performance between like devices is important as are differences in topological usage All signal bearing devices contribute to the degradation but there are some differen...

Page 6: ...serves as a natural benchmark Virtually all the amplifiers on the market are based on a push pull symmetry model The push pull symmetry topology has no particular basis in nature Is it valid to use air s characteristic as a model for designing an amplifier If you accept that all processing leaves its signature on the music the answer is yes One of the most interesting characteristics of air is its...

Page 7: ...amplifier alternates operation with a minus side Each side of a push pull amplifier handles the audio signal alternately the plus side supplying positive voltage and current to the loudspeaker and the minus side supplying negative voltage and current Problems with push pull amplifier designs associated with crossover distortion have been discussed elsewhere at length and one of the primary results...

Page 8: ...reaches the single ended bias point of the Aleph 0 it is considered a single ended Class A amplifier as the bias is provided by a current source attached to the negative power supply Beyond the single ended bias point it will operate as a push pull amplifier in the conventional sense leaving Class A at twice the bias point or about 120 watts peak into 8 ohms A very important consideration in attem...

Page 9: ...at small fractions typically 20 of their ratings For extended life we do not allow chip temperatures to exceed 80 degrees C Regardless of the type of gain device in systems where the utmost in natural reproduction is the goal simple single ended Class A circuits are the topologies of choice While it will not leave Class A on an unclipped positive signal a single ended Class A design would ordinari...

Page 10: ...any environment the amplifier is equipped with balanced inputs featuring a common mode noise rejection of greater than 60 dB Balanced operation is accomplished through a passive network tied directly into the input stage of the amplifier not with additional active input circuitry as in other products This assures that the noise benefits of balanced operation are not accompanied by the degradation ...

Page 11: ...ance 01 ohm Input Impedance 25 Kohm differential XLR 10 Kohm single ended RCA Common mode rejection 60 dB Output Noise 600 microvolts DC offset less than 100 mV after warm up Power Consumption 300 watts at 75 watts output Operating Temperature 50 degrees C Warm up time 1 hour minimum Dimensions 12 W x 12 D x 10 5 H Shipping Weight 68 lb PASS PASS Pass Laboratories 21555 Limestone Way Foresthill CA...

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