Pass Labs XP-30 Preamplifier Preview

Pass Laboratories introduced its new 3-chassis XP-30 Preamp, the flagship to its XP line or preamplifiers. The triple-chassis structure allows the XP-30 to function as a modular preamplifier consisting of a power supply and control chassis and two additional gain chassis, each of which serves one channel. The XP-30 is typically supplied as a two-channel product but it's modular design means that it can be configured to serve anywhere from one to six channels. In this way it can serve the needs of a stereo or multi-channel system. The XP-30 joins Pass Labs' XP-10, XP-15, XP-20 and XP-25 in its XP series of preamps and phono preamps.

In measurable performance, the XP-30 was designed to exceed its predecessors by generating lower noise levels, better crosstalk specifications, and greater dynamic range. We'd love to either see the specs or measure the Pass XP-30 - as the company doesn't seem to publish the specifications on its website. What we do know is that each channel provides master and slave outputs. A knob on the front of each of the gain chassis sets the slave output to be equal to or less than the master level. All connected gain chassis respond to a master level adjustment on the control chassis. Both single-ended and balanced outputs have the same gain structure and may be used interchangeably. The control chassis also supports a mono function that allows almost limitless multi-amplifier functionality.

A new low-noise volume control covers a range of 100 dB in 1-db increments and the external power supply is large enough for a small power amplifier. Its chassis houses a pair of highly efficient, low-noise Plitron transformers. The circuits use dual mono topologies that are designed to supply ample current and voltage stability to the gain stages, as well as better noise suppression and filtering. Part selection seems to be of utmost importance in this product.

Inputs

There are a total of seven inputs on each chassis. The first inputs are numbered 1-5. Input 6 has been named “Pass- Thru” and is intended for use with a home theater processor. The home theater “pass-thru” command is simply a software manipulation that selects input 6 and sets the gain to 0 dB with a minimum of keystrokes. The keystroke shortcut selects input 6 and slowly advances the volume control to step 89, starting from 0. The slow advance of level is intentional; 0dB (step 89) is appropriate for a home theater processor, it is however dangerously high for most source components. As the level advances the display will indicate each volume step with the step number and the suffix L & R (Left and Right). Once the 0dB point is reached the L & R suffix are superseded with a letter P (Pass-Thru).

At any time the volume advance for the Home Theater Bypass may be interrupted by pressing any button on the hand remote other than the Pass-Thru button. Once halted the volume may be manually set from either the front panel volume control or from the volume up ^ and volume down v arrows on the remote. Pass- Thru functionality may be over ridden allowing this input to be treated as simply as an additional user addressable input. The slow advance of level allows the user to safely cancel the incremented volume increase command and assert manual control over the pre-amplifier output level. When selected as an additional input the control chassis display will show this selection as input 6 with the letters L (left) and R (right) as suffix’s to the level setting. Input 7 is the tape loop.

Outputs

There are balanced and single ended outputs on both "master" and "slave", you may use as many of these outputs as you wish without degradation of the signal. Each output is derived from its own circuit element and is totally independent of any other outlet. On the XLR, pin 1 is ground, pin 2 is positive and pin 3 is negative.

On the RCA, by convention the center pin is positive and the outer shell in ground. When using the RCA input, the circuits internal to the XP-30 will synthesize the negative input and there after treat the signal as balanced. The XP-30 also incorporates a “tape-loop” for those users who either record or wish to insert a processor loop as a side chain. Tape out communicates directly back to the input bus, bypassing the volume control. Tape out is always active, with the exception of when Tape Input is selected (to avoid a feedback loop).

The tape loop is only available from the remote control and is selected or deselected by a single keystroke of the “Tape” button on the remote. When tape is selected from the hand remote, the display on the power supply shows a lower case "t" on the right hand side of the display. When the letter "t" is showing, the tape input is "selected" and all other inputs are "deselected", regardless of any previous settings you may have chosen. Pressing the "Tape" button a second time, cancels the command.

Notable Features

The XP-30 has a single pair of binding posts on the power-supply / control chassis which are labeled "Ext. Amp Turn-on". A 12-volt DC signal is available at these binding posts to control additional entertainment electronics. While the External Turn-on feature was specifically intended to control Pass Laboratories power amplifiers, we'd hope that it would also operate at a high enough current rating to work with amplifiers from other manufacturers. The power amplifier’s onboard stand-by switch intentionally overrides the preamplifier control with respect to the "on" command so that the power amplifiers may also be controlled manually.

The Mono function is selected only from the front panel, and is not available from the remote. When mono is selected, rather than creating a true mono signal it creates a frequency-dependent blend of signal from two chassis. The blend has been chosen such that it minimizes noise while maximizing information transfer. The two blended gain chassis are joined to one another by a special XLR cable. This was designed to address the special needs of professional audio archivists who frequently work with recordings of great historical importance and dubious quality. Professional archivists typically require circuits that transfer the last iota of intelligible detail combined with the smallest percentage of unwanted artifact (spurious noise).

The XP-30 Preamp will be available in August from authorized Pass Labs dealers at a suggested price of $16,500 (U.S. MSRP).

For more information, please visit www.PassLabs.com

Unless otherwise indicated, this is a preview article for the featured product. A formal review may or may not follow in the future.