audio research

Tube stereo preamplifier.



SP-3A (1974)
SP-3A-1 (1975)
SP-3B (1978)

SP-3C (2001)

From the ARC website

Audio Research has the reputation for the best product support in the industry, which includes service for products that date back to the beginning of the high-end industry and to the founding of our company over 30 years ago. As further support, we occasionally offer update programs for older products to extend their service life and enhance their sonic performance.

The SP3 was introduced in 1972 and was instrumental in establishing Audio Research's world-wide reputation for sonic excellence. Several thousand were sold during the period of 1972-1976 and most, we believe, are still in service today.

It is no longer possible to obtain the high voltage (525WVDC) electrolytic capacitors used in the original design. Along with this consideration, Audio Research has made significant sonic gains during the preceding 20+ years in the design of vacuum-tube preamplifiers. Therefore, it seems an appropriate time to redesign the power supply, using currently manufactured parts, and offer some synergistic sonic upgrades at the same time.

We have prepared a replacement Printed Wiring Board for the SP3's power supply using a highly regulated circuitry quite similar to that used on our present products. This will considerably extend the useful service life of this product both functionally and sonically. The new power supply operates over a very wide range of input voltage (95 Volts to 135 Volts for 120 Volt units) providing regulated DC voltages to the vacuum-tube heaters as well as regulated B+ voltages. We have added automatic muting for turn-on, power interruption and turn-off.

Along with the changes to the power supply, the input and output connectors are replaced with audiophile-grade gold-plated ones. Also, coupling and bypass capacitors on the main Printed Wiring Board are changed to brand names such as Infinicap, REL-Cap and WIMA.

The sum of these changes results in a vacuum-tube stereo preamplifier (with RIAA phono) that approaches the performance of our current preamplifier product line. You will find the bass much more well-defined and extended, the mid-range smoother and more accurate, and the high frequency range extended and more accurate. For those of your who like classic tube sound, this modification takes a large step toward accuracy while preserving the things you like about vacuum tubes.

This update applies to all versions of the SP3. Cost is US$995.00. It does not include tubes, if needed, or shipping. It is offered on a direct basis only, rather than through our dealer or distributor networks. Updates must be scheduled for timely turnaround.

If you have premium quality tubes such as NOS Telefunken, or other quality brands, we suggest you remove and keep such tubes at home, not risking the possibility of loss or damage from handling or shipping. Recommended shipping: UPS. Units sent in without tubes will be tested and evaluated sonically with our tubes installed, but will be returned without tubes unless you request otherwise. Highly modified units may be deemed unacceptable for this update.

Gold/black faceplate.
Walnut cabinet (WC-1)

MSRP (US new retail)
$695 (SP-3A)
$795 (SP-3A-1)



Frequency response ±1dB 10Hz-30kHz, IHF load
  ±1dB of RIAA 30Hz-30kHz
Distortion (THD) Harmonic distortion: Less than 0.005% at 5V RMS output, IHF load
  IM distortion: Less than 0.005% at 5V RMS output, IHF load, SMPTE method
Noise & hum High level inputs (unweighted wide-band): more than 90dB below rated output
  Magnetic phono inputs (below 10mV input) 20Hz to 20kHz: more than 70dB below rated outputs. Power line components (hum): more than 66dB
Gain 57dB, magnetic phono input, main outputs, IHF load
  34dB, magnetic phono input, tape outputs, IHF load
  23dB, high level inputs, main outputs, IHF load
  0dB, high level input, tape outputs, IHF load
Input impedance Magnetic Phono: 50K ohms typical (150 pf shunt)
  High Level: 100K ohms typical
Output impedance Less than 600 ohms @ 1kHz (all outputs). Recommended load: 20K or greater
Output polarity  
Maximum inputs 300mV RMS @ 1kHz (magnetic phono input). High level inputs overload proof.
Rated outputs Maximum output: 25V RMS @ 1kHz, all outputs
Power supplies  
Tube complement (2) 12AX7 LN, (6) 12AX7
Power requirements 120/240V, 50/60Hz, 60 Watts
Other Tone controls: Bass and treble variable ±18dB at 10Hz and 15kHz respectively
Dimensions 15 5/8" W x 5½" H x 12½ D
Weight 14 lbs. Net. 20 lbs. Shipping


Number 3 (SP-3: Full Review), Number 4 (SP-3A: Capsule), Number 5 (SP-3A: Further Thoughts), Number 8 (SP-3A Revised: Full Review)
Vol. 3 No. 5 (SP-3), Vol. 3 No. 7 (SP-3A)