Introduction
The X-2 is a balanced single ended Class A audio preamplifier combining new
design thought applied to a traditional topology and the experience of over twenty
five years of amplifier design. The circuitry is based loosely on that of the Pass
Aleph P, but has been revised for manual operation without remote control.
This product design flows from a commitment to create the best sounding product: a
simple circuit with the most natural characteristic. The X-2 integrates power Mosfet
devices and balanced single ended Class A operation in a simple topology in order
to deliver the most natural sound possible.
The design of the X-2 has been kept simple and functional. An input selector switch
selects between the four available inputs. The first input can be either balanced or
single ended, and the other three inputs are single-ended. The fourth input can be
utilized as a standard input or as a tape monitor input. The input selector along with
a separate tape selector allows monitoring recordings or recording from a source
different from the one you are listening to.
The X-2 minimizes the number of components in the signal path, and yet retains
superior objective and subjective performance. It exemplifies the state of the art in
exploring how much quality is obtainable with very elementary gain stages. Each
gain stage consists of a single Mosfet power transistor operated in 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 providing balanced and unbalanced outputs.
The gain stage uses an ultra-matched pair of power Mosfets biased by a single
constant current source. The signal path of the X2 is as simple as you can get and
operates entirely without negative feedback. In spite of this extreme simplicity the
circuit delivers as high as 70 volt balanced peaks. At levels which merely clip
amplifiers the distortion level is about .007% across the audio band, with a
frequency response which is flat to 200 KHz.
The volume control has 24 matched sets of precision metal film resistors on a
Swiss-made stepped switch which offers a 60 dB range and .1 dB tracking.
Two separate toroidal power transformers provide an unregulated 160 volts which is
then actively and passively regulated down to 130 volts using separate regulator
systems for each channel. The noise of these power supplies is on the order of 20
microvolts. The preamplifier has a muting relay with a control circuit which delays
output connection on turn-on and which mutes the preamp in case of insufficient line
voltage for proper regulation.
Thank you for purchasing this product. We at Pass Labs hope that it provides you
with the sonic experience that you are seeking, and that your enjoyment of it is equal
to the effort we put into its design and construction.
Setup
