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SP20 Vacuum Tube Preamplifier

Audio Research REF 10

As a result of the ever-increasing demand by dealers and distributors for a full-function preamplifier with a level of performance substantially above that of the SP17, we are pleased to introduce the striking new SP20 vacuum-tube preamplifier. Influenced by some of our classic groundbreaking SP preamplifiers but with performance that is only achievable by our best LS- and PH-series designs, the SP20 offers inspirational performance combined with real value.

The look is reminiscent of classic Audio Research components, but is totally modern with a clean, purposeful esthetic. The front panel sports a new 4.3” LCD touchscreen, with two large rotary knobs on either side. For the first time ever on an Audio Research preamp, there is a ¼” headphone jack, accompanied by three buttons for Power, Mute, and Speaker off.

Those large knobs rotate fully, are optically-coupled and speed sensitive; turn it slowly and the volume will change incrementally; a quick turn one way or the other will raise or lower the volume by a large amount. Also for the first time, the Input selector is on the left, the Volume control is on the right.

Through the touchscreen one can change Inputs, select Stereo or Mono, Mute, adjust Phase, adjust left-right Balance, and adjust the phono input Load (50, 100, 500, 1000 or 47k Ohms). Through a Settings menu, you can customize other items: change input names, adjust gain offset for each input, change volume presets, adjust display brightness (or turn off), and check Tube Hours (or reset). When the tube hour meter reaches 4,000 hours, the Settings icon will turn red to warn the owner it is time to change the tubes.

In addition to the Phono input, there are four other single-ended inputs, two balanced inputs, separate Monitor-in and Record-out, and two pairs of balanced outputs. There is also an RS-232 port, IR-input, 12V trigger, and a 15A IEC connector. The SE4 input can be configured as a home theater pass-through.

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. Bandwidth is extraordinary: Line -3dB 0.8Hz – 220kHz, Phono +/- 0.4dB 5Hz—80Hz. Gain of the line section is 13.8dB (BAL), and gain of the phono section is 58dB, 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, inserted simply as an inexpensive feature to add to the list; 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.

Audio Research REF 10 Audio Research REF 10

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 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
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 19V RMS Balanced, 9V RMS SE. Phono: 70mV RMS at 1kHz.
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.
Channel Separation Line: > 105dB Balanced output
Phono: >76dB to Record output
Headphone: >62dB
Controls Rotary Volume (104 steps), Rotary Input selector. Push
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%. 
Noise Line: <-101dBV volume at max.
Phono: <-77dBV to Record output 
Headphone: <-88dBV volume at max.
Tube complement 4 6H30 dual triode.
Power requirements 100 - 135VAC 60Hz (200 - 270VAC 50/60Hz) 77 watts maximum. Standby 2.7 watts.
Dimensions Width 19" (48 cm) 
Height 5.25"(13.4 cm) (standard rack panel) 
Depth 16.5"(42 cm) D.
Weight 17.8 lbs. (7.4 kg) Net; 
27.8 lbs. (10.5 kg) Shipping.

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