Pass Labs X2.2 - Manual (Page 7)

7 X2.2 Owner’s Manual
the total mismatch to about .1%, for a common-mode rejection of
approximately -60 dB.
The input system of the preamplifier will exhibit full common-mode
noise rejection with passive balanced sources, where the negative
input is connected to ground at the source through the appropriate
source impedance. This allows adaptation of unbalanced sources to
balanced operation with passive cable connections in a manner that
achieves the noise rejection of active balanced sources.
The use of a micro-controller allows all of the preamplifier functions
to be repeatable and accurately controlled. The micro-processor
only controls the functions of the preamplifier. At no time does
any of the input or output signal come into contact with the digital
control signals. The digital circuits are powered by a power supply
that is completely separate from the analog supply. Should it ever be
necessary to update the software that controls the functioning of the
preamp only the socketed micro-processor need be changed.
The power supply for the X2.2 consists of a toroidal power
transformer delivering an unregulated +/- 45 volts which is actively
regulated before feeding passive filtering and powering the constant
current sources which bias the gain stages. Each channel has its own
regulation. The power supply noise reaching the circuit is on the
order of one microvolt, and the little of that which gets through the
circuit is rejected at the output in a balanced system. The relays and
control systems are regulated independently, and all digital circuitry is
isolated from the power supply.
Muting relays, which delay connection during turn-on and shut off
the output when insufficient power supply is available to maintain
regulation, guard the output of the preamplifier. The preamplifier
is designed to run constantly, and will exhibit optimum measured
performance within about 10 hours of turn-on.
The X2.2 consists of a single chassis.