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Product Description

Vacuum Tube Line Stage Preamplifier with Phono Stage

Influenced by some of our classic groundbreaking SP preamplifiers, the SP20 takes visual cues from past Audio Research products while incorporating our latest designs and technologies. The SP20 is a full-function line stage which incorporates a phono preamplifier and, for the first time ever on an Audio Research preamp, there is a ¼" headphone jack. Front panel controls have been minimized to two rotary controls and an interactive touch screen display, along with power, mute and output selector buttons.

The interactive touchscreen has been designed to take full advantage of the feature set the SP20 offers, and operation is intuitive and easy-to-use. Numerous adjustments allows customization to the performance and display of the SP20 for seamless system integration, including input naming and gain offsets, volume presets, and tube hours. System checks have been put into place to alert when tubes have exceeded standard serviceable hours (4,000), and a low line auto mute function engages in the event of a power brown-out.

The SP20 is fully balanced, pure Class-A with zero feedback. There are seven levels of voltage regulation, a large power supply, and a very low-noise R-core power transformer. Both the line and phono stages feature low-noise JFET inputs and 6H30 (2 per section) outputs. The latest high performance coupling and bypass capacitors are used in both stages. Both the line stage and phono preamplifier offer extraordinary frequency response and low noise. The phono section provides 58dB of gain, so the SP20 can be used with a wide variety of phono cartridges, including moderately low output moving coils.

The headphone output is no mere afterthought; it is a low-distortion, high-performance vacuum-tube headphone amplifier designed to comfortably drive a wide impedance range of headphones. The button next to the headphone jack switches off the main (amplifier) outputs for headphone listening, or it switches off the headphone jack for speaker listening.

All of these developments would be for naught if the SP20 did not delight sonically, which it does with ease. The presentation is so relaxed and natural, transparent and solid with great dynamics and impact. Never threadbare, sonic images have texture and a luminous 3-D quality. The SP20 delivers musically, with an ability to effortlessly drive your tube or solid-state amplifier.


  • FREQUENCY RESPONSE: Line: +/- 3dB 2 Hz to 80 kHz; -3dB 0.8Hz to 220 kHz, Phono: +/- 0.1dB of RIAA 10Hz to 20kHz; +/- 0.4dB 5Hz to 80kHz, Headphone: +/- 0.05dB 20Hz to 20kHz; -3dB 0.8Hz to 220kHz
  • DISTORTION: Less than .01% at 2V RMS BAL output.
  • THD+N: Line: <.003% at 2V RMS, Bal output, Phono: <.005% at 3V RMS output, to Record output, Headphone: <.009% at 1V RMS output
  • GAIN: Line: 13.8dB, Processor: 0dB, Phono: 58dB @ 1KHz to Record output, Headphone: 11.3dB
  • NOISE: Line: <-101dBV volume at max, Phono: <-77dBV to Record output, Headphone: <-88dBV volume at max.
  • CHANNEL SEPARATION: Line: > 105dB Balanced output, Phono: >76dB to Record output, Headphone: >62dB\
  • SIGNAL TO NOISE RATIO: Line: >125dB Balanced output, Phono: >94dB to Record output, Headphone: >110dB
  • RATED OUTPUTS: Line: 2V RMS (1V RMS SE) into 200k ohms balanced load (maximum balanced output capability is 18V RMS at less than .5% THD+N at 1kHz.). Phono: 0.5V RMS into 100k load at Record output (maximum output capability is 25V RMS). Headphone: 6V RMS maximum into 30 to 300 ohm load.
  • INPUT IMPEDANCE: 120k ohms Balanced, 60k ohms SE; Phono impedance programmable (100, 200, 500, 1000 or 47k ohms w/200pf unbalanced).
  • OUTPUT IMPEDANCE: 500 ohms Balanced, 250 ohms SE; 1000 ohms Record Out SE; <.05 ohms Headphone SE.
  • OUTPUT POLARITY: Non-inverting. 
  • MAXIMUM INPUT LINE: 19V RMS Balanced, 9V RMS SE. Phono: 70mV RMS at 1kHz.
  • CONTROLS: Rotary Volume (104 steps), Rotary Input selector. Push 
  • BUTTONS: Power, Mute, SPKR Off. Interactive Touch Screen. Rear RS-232 control and Remote IR input.
  • POWER SUPPLIES: Electronically regulated low and high voltage supplies. Automatic 30 sec. warm-up/brown-out mute. Line regulation better than .01%. 
  • TUBE COMPLEMENT: 4 6H30 dual triode.
  • POWER REQUIREMENTS: 100 - 135VAC 60Hz (200 - 270VAC 50/60Hz) 77 watts maximum. Standby 2.7 watts.
  • DIMENSIONS: Width 48 cm, Height 3.4 cm, Depth 42 cm
  • WEIGHT: 7.4 kg) Net