Phase Linear 4000 Series Autocorrelation Preamplifier - Restored

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Stunningly beautiful preamp from Phase Linear, and a great match to our Phase Linear 700 Series amplifier that's also listed for sale. 

The 4000 Autocorrelation Preamplifier was a collaboration design by Bob Carver and Bill Skinner. It was designed to expand or decompress the sonics of recorded material. In audio parlance, it's called dynamic headroom. In the midst of all the knobs and toggles was the four channel balance joystick.

The 4000 had the capability of controlling up to six components: a tuner, two tape decks, two turntables and an auxiliary input. It had three switched and three unswitched AC plugs. The 4000 was manufactured from 1973 to 1977. It retailed for $600 but the price rose 10 % in 1977. It's still highly sought after today.

This example is in near perfect condition, with no signs of use or abuse. Working perfectly and there are also signs that this unit was previously and correctly restored. Such as Cardas RCA Jacks on all rear connections and select electrolytic capacitors replaced with Nichicon.

Please see our last photo or the linked manual below for full specifications:

Phase Linear 4000 Preamplifier - Manual

Our Testing Process for Preamplifiers at SkyFi:

We start with a visual inspection of all internal components to make sure there are no signs of stress or aging. Capacitors are checked for telltale sings of bulging or leaking, resistors are checked for signs of overheating or cracking, and transistors are checked for signs of stress or damage. Special attention is paid to the power supply which is the most common source of failure for preamps. We then power up the unit and run a simple 1k sine wave while monitoring the low voltage output on an oscilloscope for signs of distortion or noise to get a baseline.

At this point we will lubricate and clean all switches and potentiometers (that are not sealed) with a high quality contact cleaner, and then re-test all functions for any signs of noise or scratching.

Final testing involves putting actual music through the preamplifier We have learned over time that some issues are only noticeable to a trained ear while listening to a familiar source material. Our test bench has reference vintage Kef speakers that we are super familiar with which will quickly reveal any discrepancies. Some preamps will then move into the listening room where they will be tested with our in-house reference system.

Please click here for detailed specifics regarding our specialized packing process that separates us from the rest.