Audio Research SP-3A-1 Vintage Tube Preamplifier - Collector Grade Restoration - Reviewed By The Audiophiliac

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This is a collector grade restoration of a classic and well regarded preamp from Audio Research. The exact model designation is SP-3A-1.

Many consider the SP3 as the finest preamp ARC ever produced. Its classic looks and reliable operation have made this piece a favorite among collectors.

PLUS Steve Guttenberg "The Audiophiliac" recently reviewed this EXACT item on his YouTube channel!

We're huge fans of the SP3 in all its variations, and this is one of the best we've seen. To help demystify the SP3 check out this video from our channel:

This comes to you with it's rare original wood case (!) which takes the looks to another level. Absolutely gorgeous.

An excellent match for any vintage system using speakers that might require a bit of boost from the built-in tone controls.

You're not going to find a finer electrical restoration. Even the tubes are upgraded to "new old stock" GE JAN 12AX7.

All upgrades were aimed at improving reliability and long term performance, while maintaining every last bit of the original sonic signature.

This model also features an upgraded Alps 100K stepped potentiometer offering a much better feel and channel balance for volume adjustments.

A spare lamp for the green power indicator will be included, along with a spare fuse.

Restoration Notes:

This preamp underwent a restoration focused on preserving the original character of the unit, while making it safe to operate at today’s AC mains voltages.

The power supply was completely recapped with modern discrete equivalent components with increased voltage handling. Any heat stressed resistors on the power supply board were replaced. The Zener reference diodes for the power supply voltage regulator were replaced and elevated off of the PCB. These diodes were hand selected for proper performance at operating temperatures. The thermal transfer compound for the series pass transistor was also refreshed to ensure proper heat dissipation.

The main preamp PCB was left untouched. All resistors were tested to verify that they were within tolerance.

All controls were cleaned and tested. The original volume control showed signs of out of spec channel balance and was replaced with an ARC approved Japanese Manufactured Alps Control. The Bass and Treble controls were rebuilt to address a carbon track gap issue.

All tubes are freshly installed NOS GE JAN 12AX7WA, which were carefully selected and arranged in circuit for optimal channel balance in both the phono and line stages.

Click here for a PDF copy of the SP-3A-1 Owner's Manual

The SkyFi Testing Process for Preamplifiers:

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.

Technical Specifications:

Frequency response:
15Hz-30kHz, ±1dB

Distortion (THD):
0.005% at 5V out

Maximum output:
25V at 1kHz

S/N Ratio:
90dB (Aux input, no ref. level given)

Dimensions:
15 5/8" W by 5" H x 12½ D

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