audio research

Tube stereo line stage.

From the ARC website

Since its introduction more than three years ago, the original REFERENCE 1 preamp has established itself around the world as a benchmark in line-stage design and sonic performance. And compared to other, more costly competitive designs, the REF1 was perceived to have higher value per dollar as well.

That tradition of sonic leadership is advanced again with the introduction of the REFERENCE 2 line preamplifier, at $9995 U.S. MSRP. This is one of those rare products that when first heard, truly justifies the word breakthrough. The REFERENCE 2 represents that much of an advance over the REF1, by every important sonic standard. It's bigger, bolder, richer, better focused with greater delineation of inner detail than you,ve ever experienced. The dimensionality and, perhaps most importantly, the naturalness and dynamic immediacy take the listener inside the music in a thrilling, intimate way. Whatever music you play through the REF2 becomes more intuitively meaningful and comprehensible, with less of the electronic curtain that has been the plague of more conventional music reproduction components.

This highest level of resolution and musicality has been accomplished in large measure by all-new audio and power supply circuits, incorporating tube rectification (via one 5AR4) and tube regulation (via one 6L6) of the power supply (also packed with the newest Infinicaps, and one 6922). Gain is provided by eight selected 6922 twin triodes, like the REF1. Redesigned toroid transformers also contribute to improved dynamics.

Mechanically, the REF2 is almost identical to its predecessor, with one significant exception: the input selector now offers a unity-gain A-V processor pass-through, allowing easy incorporation into video systems for both stellar music performance and convenient gain control via the processor's master level control when desired. Now, you can easily have it all in one flexible system. Importantly, the REF2 circuit also effectively prevents any possibility of input-signal overload while preserving incredible sonic purity.

Chassis configuration and size, front-panel controls (with the exception of the processor-input labeling) and rear-panel input / output configuration are identical to the REF1. A total of eight balanced and single-ended inputs are provided, plus two sets of main outputs and record out. In addition, all front-panel functions are accessible from the included remote control. Because of this mechanical similarity, REF1 owners will be able to upgrade their REF1 units to full REFERENCE 2 configuration, complete with new 3-Year Limited Warranty. This is not be an inexpensive update, as the original model is essentially taken apart, then reassembled using new audio and power supply boards, two new toroidal transformers, new front and rear panels, and all new vacuum tubes. MSRP of the factory upgrade is $4495, plus shipping to / from the factory (no field update kit available).




From the ARC website

With the enthusiastic response to the introduction of the LS25MKII, it quickly became clear that the path was also open to improving the REFERENCE TWO flagship. We are happy to announce that similar dramatic enhancements in the REF2MKII are now available at an unchanged U.S. suggested price.

How advanced is the MKII in sonic performance? It is as much an improvement as the LS25MKII was over its predecessor -- which is to say it is immediately audible and musically profound. Image focus, clarity and a sense of body are all heightened -- where by contrast the original version is simply less vivid overall. Dynamically, too, the MKII picks up the pace in a startling manner, making the rhythmic line and structure of any musical selection much more evident and understandable. The ebb and flow of a bass line, percussive textures, and time changes now make more musical sense as you hear them revealed by the greater immediacy and dynamic freedom of the REF2MKII. Finally, the MKII presents the music with a solidity and focus and coherence that is simply not present to the same degree in the original. From top to bottom, then, the REF2MKII is a another advance of the state of the art in line-level preamplification.

These enhancements are also available to original REF2 owners as a factory MKII upgrade. A two-year warranty extension is included. REF1 owners can update to the REF2MKII with a three-year warranty extension included. New tubes are included in each update.

On the technical side, the REF2MKII has major changes to both the power supply and analog circuits requiring two new circuit boards and one new toroid. The input circuit board and the digital logic circuit board remain unchanged. The power supply now has newly designed regulator circuits with wideband response more closely approximating that of the active analog circuitry -- providing better dynamic response to the changing demands of the input signal. The analog circuitry now uses J-FETs in the input amplification stage, as several of our newest product upgrades do. The second amplification stage uses a 6H30 twin triode for additional gain, which is directly coupled to another 6H30 serving as a cathode follower / output driver. The 6H30, in current production in Russia, was originally designed for military use and offers a service life of up to 10,000 hours. Finally, the analog circuitry also uses our previously patented cross-coupled circuitry between the input stage and the vacuum-tube stage for more accurate signal tracking and lower distortion.

In terms of input / output configuration and control functions, the MKII is unchanged from the original REF2. However, as on the LS25MKII, a 12V output has been added to the rear panel for remote powering of other linked components (this is also installed on factory update units).

The REF2MKII will without question take top honors again from reviewers around the world as the finest stereo line preamplifier available anywhere, at any price.


MSRP (US new retail)


Frequency response +0 -3dB 0.5Hz to 60kHz at rated output.
Distortion (THD) Less than .015% at 2V RMS Balanced output.
Noise & hum 20µV RMS residual IHF weighted balanced noise output with gain control minimum (100dB below 2V RMS output, 97dB below 1V RMS SE output).
Gain Main output: 18dB Balanced, 12dB Single Ended output
Tape output: 0dB. (Processor input: 0dB Balanced. Aux 1 input: 13dB Balanced.)
Input impedance 132K ohms Balanced, 66K ohms SE. Inputs (8): tape, tuner, phono, CD, video, aux 1, aux 2, processor, (XLR and RCA connectors).
Output impedance 400 ohms Balanced, 200 ohms SE main (2), 20K ohms minimum load and 2000pF maximum capacitance. Outputs (3): 2 main, 1 tape (XLR and RCA connectors).
Output polarity Non inverting
Maximum inputs 14V RMS maximum Balanced, (7V RMS SE).
Rated outputs 2V RMS (1V RMS SE) into 100K ohm balanced load (maximum balanced output capability is 30V RMS at less than 0.5% THD at 1kHz).
Power supplies Electronically regulated low and high voltage supplies. Automatic 45 sec. warm-up/brown-out mute. Line
regulation better than .01%.
Tube complement REFERENCE 2: (8) 6922/E88CC dual triodes, plus (1 each) 5AR4, 6L6GC, and 6922 in power supply.
  REFERENCE 2 MKII: (6) 6H30 triodes; (1) 6L6; (1) 5AR4.
Power requirements 100-135VAC 60Hz (200-270VAC 50/60Hz) 130 watts maximum. (108W typical)
Other Controls: Gain (125 steps), Balance, Select Record, Select Input. Toggle switches: Power/Off, SE/Balanced Input, Invert/Normal, Mute/Operate.
Dimensions 19" (48 cm) W x 7" (17.8 cm) H (standard rack panel) x 15.5" (39.4 cm) D. Handles extend 11/2" (3.8 cm) forward of the front panel.
Weight 31 lbs. (14.1 kg) Net; 44 lbs. (20 kg) Shipping.


Issue 123 (REFERENCE 2), Issue 135 (REFERENCE 2MKII)
Vol. 23 No. 9 (REFERENCE 2)