Audio Research SP-3 - Vintage All Tube Amplifier - Complete Collector Grade Restoration w/ Amperex Tubes

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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 and this is an example of the very first production run for this piece.

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.

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. An NTC thermistor was also added to limit initial inrush current. 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 aside from a pair of low value axial electrolytic capacitors, which were replaced with modern equivalents.

All controls were fully cleaned and tested. The original volume control showed signs of out of spec channel balance, so it was replaced with an ARC approved, Japanese Manufactured, Alps Control.

**Note this has two front faceplate red lamps rather than a green and a red. We were unable to source a green one from ARC direct or other official sources.

All tubes are Orange Globe Amperex 12AX7A's which were arranged for optimal channel balance in both the phono and line stages.

Click below to add our recommended matching cables from Kimber Kable, all brand new as SkyFi is an official Kimber dealer.

Kimber Kable - RCA Interconnects

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

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.