Pass Labs pre-amplifier owner manual

X0.2 Owner’s Manual

With balanced operation, the common mode rejection of the preamp reflects the intrinsic common mode rejection of the topology, the matching of the gain devices, and the matching of the attenuator channels. In this case we have been able to keep the total mismatch to about .1%, for a common mode rejection of greater than -60 dB.

The input system of the pre-amplifier 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 pre-amplifier functions to be repeatable and accurately controlled. The micro-processor only controls the operational functions of the pre-amplifier. At no time do any of the input or output signals come into contact with the digital control signals. The digital circuits are powered by a power supply that is completely separate and isolated 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 analog power supply for the X0.2 consists of a toroidal power transformer delivering an unregulated +/- 45 volts which is then 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 differentially rejected at the output in a balanced system.

The relays and control systems are regulated independently. All digital circuits receive their power from a separate toroid, which, like its analog counterpart, is also double regulated, and carefully filtered.

Muting relays, which delay connection during turn-on, additionally shut off the output when insufficient power supply is available to maintain regulation, thus guarding the output of the pre-amplifier. The pre-amplifier is designed to run constantly, and will exhibit optimum measured performance within about 10 hours of turn-on. For this reason a power switch is intentionally omitted.

The X0.2 consists of three machined aluminum chassis. Likewise, the remote control device is ensconsed in its own palm sized aluminum chassis. All four chassis components are machined from solid aluminum material on computer controlled vertical milling machines. There are no sheet metal components is this product. All engraving is done by laser to make it easy to read and provide a durable and attractive finish.

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