Pass Labs X1 owner manual Other Design Comments

Other Design Comments

X1 Owner’s Manual

takes imagination and hard work to get as much of these as possible at once without trading them off adversely against each other.

We recommend the use of the balanced output mode where possible. It will retain the character of the input mode, but offers less distortion, less noise, more gain, and more voltage swing, without compromising the sound.

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 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. There is a single custom made shielded cable that connects the power supply to the main preamplifier module. The power supply cable does not carry any audio signals or digital clock lines and is filtered against noise.

The power supply for the X1 is contained in a separate chassis and consists of a toroidal power transformer delivering an unregulated +/- 45 volts which is actively regulated before feeding passive filtering which powers the constant current sources that bias the gain stages. Each channel has its own regulation. The power supply noise reaching the circuit is on the order of a 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 from a separate toroidal transformer. All digital circuitry is isolated in the power supply control unit. The power

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