PassLabs Aleph P Owners manual

Pass Laboratories

Aleph P Owner's Manual

Introduction

The Aleph P is a single ended Class A audio preamplifier, the first produced by Pass
Laboratories. It combines completely new design thought applied to a traditional topology
and the experience of twenty five years of amplifier design. This manual applies to the
second version of the Aleph P, which incorporated circuit improvements and remote control
operation.

This preamplifier flows from a commitment to create the best sounding product: a simple
circuit with the most natural characteristic. The Aleph P integrates power Mosfet devices
and single ended Class A operation in a simple topology in order to deliver the most natural
sound possible.

The circuitry of the Aleph P breaks new ground in simplicity and performance. Each gain
stage consists of a single Mosfet power transistor operated “common source” mode. One
such circuit amplifies each signal polarity of a balanced input signal, and their operation is
inter-coupled to allow optimal operation with both balanced and unbalanced input signals
while still providing balanced and unbalanced outputs. It retains the important simple single­ended characteristic while operating either single-ended or balanced.

It is unique in providing superior flexibility and performance with balanced and unbalanced
inputs and outputs, converting one to the other as desired without switches or adapters.

The Aleph P absolutely minimizes the number of components in the signal path, and yet
retains exemplary objective performance specifications. More importantly, it pushes the
edge of the art in exploring how much subjective quality is obtainable with a new but very
elementary gain stage.

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 preamplifier myself. If you have questions,
comments, or problems, please feel free to contact 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: ____________________

Next page: Distortion curve of your particular preamplifier at 1 kHz from .1 to 10 volts

Setup

The preamplifier has four sets of input connections, two sets of output connections, an input
selector and three level controls. Optionally, it also has a remote control.

It also has an AC line power connection. The amplifier's voltage and current rating are
indicated on the rear. It will be either 240 volts, 120 volts, or 100 volts. A .5 amp 3AG slow
blow fuse is provided with 100-120 volt units, and a .25 amp slow blow fuse is provided with
220-240 volt units. The frequency rating of the power supply is 50 to 60 Hz. The
preamplifier typically draws 25 watts during operation.

We have provided a standard AC power cord which fits into the line receptacle at the rear.
The preamplifier is equipped for operation with an earth ground provided by the AC outlet.
Do not defeat this ground. The chassis and circuit ground of the preamplifier is connected to
earth through a power thermistor, which gives a ground connection but helps avoid ground
loops.

The four input connections on the rear are pairs of XLR and RCA connectors with right and
left channels indicated. If your signal source is balanced, you may use the XLR input
connectors. On these connectors, pin 1 is grounded, pin 2 is the positive signal input, and
pin 3 is the negative signal input.

If your signal source is unbalanced, input will occur through the RCA input connector, which
is in parallel with the XLR connections 1 and 2. For operation with unbalanced inputs, a
shorting plug is provided between pins 1 and 3, shorting the negative input to ground, and
providing optimal performance.

The unbalanced input impedance of the preamplifier is a nominal 10 kOhms. In balanced
mode, the input impedance is higher, with a differential impedance of 20 kOhms.

Next to the inputs on the rear panel, the preamplifier offers tape outputs through both XLR
and RCA connectors. This output is a direct connection to inputs 1, 2, and 3 when they are
selected from the front panel. Input 4 is deliberately not available through the tape output
connection. Input 4 is designated for use with a tape recorder if you have one, and we have
arranged that it will not place its output on the tape out, which will prevent you from
accidentally creating a feedback connection with your tape machine.

At the left hand side (viewed from the rear) of the rear panel, two male XLR connectors and
two RCA connectors are used for the main output. On the XLR, pin 1 is ground, pin 2 is
positive, and pin 3 is negative. The RCA connector’s ground is in parallel with pin 1 and the
RCA hot is attached to pin 2. You may use either of these connectors for balanced or
unbalanced operation.

The circuitry of the preamplifier is such that it will drive any impedance without distortion,
however as the load impedance goes down, you will experience a reduction in gain. The
preamplifier will act as a maximum plus and minus 20 ma current source into a dead short.