| The X2 is a non-remote control line stage preamplifier
that accepts both single-ended and balanced inputs. This preamplifier is a further example
of the "less is more" design philosophy of Pass Labs. The product styling is
similar to the other "X" series products. The design of
the X2 has been kept simple and functional. The circuit consists of a single MOSFET gain
stage operated in balanced single-ended Class A. 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 volume control has 24 matched sets of precision metal film resistors
on a Swiss-made stepped switch providing a 60 dB range and .1 dB tracking.
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,
with the direct coupled input signal appearing at the Gates of the Mosfets and the output
signal at the Drains.
The gain stage of the X2 operates entirely without negative feedback. In
spite of this extreme simplicity the circuit delivers as much as 50 volts rms balanced
output (high gain mode). 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.
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.
The chassis is 17" wide, 3.5" tall with the feet, and
11.5" deep, and is milled entirely from solid aluminum stock. There is no sheet metal
in the product. The face plate is finished light instrument gray anodize. The preamplifier
weights 35 lbs. |
