Audio Research SP-3 Vintage All Tube Preamplifier - Complete Collector Grade Restoration

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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 SP3 Series A.

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.

Check out our Audio Research SP3 Series video to understand the differences between the different SP3 iterations:

 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.

All tubes are Audio Research official branded 12AX7's.

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

Repair Notes:

The power supply board was fully restored - featuring all new rectifier and zener diodes, select power resistors, and all new high quality long life electrolytic capacitors.

The pass transistor for the main B+ voltage regulation was replaced with a NOS equivalent, along with fresh thermal compound.

Select heat stressed components were replaced in the main preamp board.

All controls and connections were cleaned and thoroughly tested.

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.

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.