Pass Labs X1 Two Piece Preamp, Just Serviced

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General:
Stunning two-piece preamp from Pass Labs in perfect cosmetic and working condition. We just serviced it by installing a brand new display and replacing the the volume encoder. Working perfectly and fully tested in our lab and listening room and includes the remote and the manual.

Fully balanced design.

This item belonged to a famous musician which we will share after purchase.

From a Positive Feedback review written by John Brazier:

"With the absence of any criticisms, it is not a stretch to assume that I believe the X1 to be near the top of the price/performance ratio. For the money, I do not think you can do better, especially if your preferences are transparency in the sense of wanting the preamp to get out of the way and let the other components do their job.

My set-up has been going through a major overhaul over the last couple of years. Circumstances have been such that I have been able to chase the level of performance that I did not think I could ever obtain. The last piece of this puzzle has been the selection of a preamp. With the X1, I did not hear the need to look any further for the "right" unit to fit within my set-up.

I now own the X1. Just give it a listen you will be amazed at what you don't hear; you might end up owning one too!"

From the X1 Owner's Manual:

The X1 is an ultra high quality minimalist audio preamplifier that features a remote control and external power supply. It combines a completely new circuit topology with traditional construction representing thirty five years of amplifier design.

This preamplifier flows from a commitment to create the best sounding product: a simple circuit with the most natural sonic characteristics. Derived from US Patent # 5,376,899, the X1 integrates power MOSFET and JFET devices in a simple Class A
topology in order to deliver the finest sound possible.

The patent-pending Super-Symmetric gain circuitry is unique in providing superior flexibility and performance with both balanced and unbalanced inputs and outputs, converting one to the other as desired without extra circuitry and without performance degradation.

The X1 minimizes the number of components in the signal path, and yet retains exemplary objective performance specifications. It pushes the edge of the art in exploring how much subjective quality is obtainable with a new but very elementary gain stage.

The X1 employs a new type of volume control that offers an order of magnitude better performance than seen before in an electronic control. It provides over 60 dB of range, large voltage swing and very good measured performance. Most importantly it is subjectively outstanding; better than any potentiometer we know of. We are justifiably proud of this new device, which is registered as having a patent pending.

Ownership:
Single Owner

Connections:
RCA and XLR on all Inputs/Outputs. Removable IEC Power Cord. Proprietary Umbilical.

General Sound:
Neutral sound with little to no coloration

Cosmetic Condition:
8/10 = Very Good. Excellent front faceplate, one minor flaw on chassis side or top. See our detailed rating description here.

Working Condition:
Working perfectly and tested in our lab and listening room.

Included:
Unit, remote, and power cord.

Packing:
Will be packed using our highly developed in-house process and custom packing materials.Specs:
- Gain: 4dB or 14dB.
- Freq. Response: -3dB @ 2Hz, -3dB @ 100kHz.
- Distortion @ 1KHz: <0.1% THD typical, 0.003% @ 2V.
- Output Impedance: 360 Balanced, 150 Single-ended.
- Input Impedance: 66K Balanced, 33K Single-ended.
- Output noise floor: -125dBV ref to 10V output.

Dimensions - Each Chassis
17"W x 3.5"H x 11.5"D

Weight:
46 lbs.

Link to Manual:
Click Here

Recommended Cables:

Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

Kimber Kable - BALANCED XLR Connectors - Better

Kimber Kable - BALANCED XLR Connectors - Best

Kimber Kable - Power Cords - Better

Kimber Kable - Power Cords - Best

Testing Process:

We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect the PCB’s for discoloration from resistors or transistors that may have been running hot. On vintage units we often spot check select capacitors for value and ESR.

When we first power on a preamplifier we connect its RCA output to a Sencore PA81 Power Analyzer which simulates real world loading conditions and gives us an oscilloscope interface. The first order of business is checking that the volume control works smoothly throughout its entire range with acceptable channel balance. This is accomplished by feeding a 1KHz sine wave into one of the preamp’s line level inputs while monitoring the preamp’s output on an oscilloscope. We then switch to a 1KHz square wave to test the tone controls, loudness function, and filters where applicable. During this step we are watching for equal alteration of the test signal by both channels. This also helps us identify dirty controls that will need treatment. Once the basic line stage functions are verified, we test each input individually. This is especially important for devices that use relays to select their sources. If the preamp is equipped with a phono stage we test that as well. We use an inverse RIAA filter which allows us to feed a reference test signal into the phono input with the proper RIAA equalization and level. A square wave or sine sweep is used to verify that the device’s phono stage is faithfully reproducing the RIAA curve. If the preamp under test has balanced inputs and/or outputs these are tested as well.

We finish up our bench testing with a listening test with our bench amplifier and reference speakers. During this test we check for hum or hiss that may not have shown up in earlier testing. We also check that all of the tone controls and filters perform as expected. If the preamplifier has remote control functions these are also tested. Preamps with tube circuits or complicated power supply topologies are connected at our long term test rig for extended stress testing under real world conditions.