Audio Research LS2B MKII - Tube / Solid State Hybrid Line Stage Preamplifier
The Audio Research LS2 preamp came in multiple versions and variations beginning in 1991. Line stage in ARC terminology means that it does not include a phono preamplifier.
This version, the LS2B MKII released in 1992, is the last and best of them all. It features balanced inputs and outputs (hence the 'B"), and remote control capability.
It's a wonderful sounding hybrid tube/solid state design which allows the internal 6922/E88CC twin triode tube to induce just the right amount of warmth into the signal path.
In overall great condition and in rare black finish. We have ordered an official replacement remote from ARC which will be included with your purchase.
1991 (LS2) / 1992 (LS2B)
LS2 and LS2B (Balanced).
ORIGINAL 1991/1992 MSRP
LS2 MKII: $2,650
LS2B MKII: $2,995 = ($5,500 in 2020 today's dollars)
± .5dB, 1Hz to 100Hz, -3dB points below 0.1Hz and above 300kHz
Less than .01% at 2V RMS output (typically less than .005% in midband)
NOISE & HUM
20µV RMS residual 1HF weighted noise at main unbalanced output with gain at minimum (100dB below 2V RMS output). xxx Balanced input noise 100dB below 1V input.
LS2: Main Output: 18dB. Balanced output: 24dB. Tape output: 0dB (Optional 12dB gain reduction). LS2 MKII: Main Output: 18dB. Balanced output: 24dB. Tape output: 0dB (Optional 9dB gain reduction)
LS2: 50K ohms. LS2: 50K ohms unbalanced, 3 megaohm balanced.
LS2: 200 ohms main output. 500 ohms Balanced 1, Balanced 2 (10K ohms minimum load and 2000pF maximum capacitance). LS2 MKII: 200 ohms main output. 400 ohms Balanced 1, Balanced 2 (10K ohms minimum load and 2000pF maximum capacitance)
LS2: 20V maximum. LS2 MKII: 20V maximum unbalanced, 8.5V maximum balanced.
LS2: 2V RMS 1Hz to 100kHz into 60K ohm load (maximum output capability is 10V RMS (20V RMS balanced) output at 05% THD at 1kHz into a 10K ohm load). LS2 MKII: 2V RMS 1Hz to 100kHz into 60K ohm load (maximum output capability is 30V RMS (60V RMS balanced) output at 05% THD at 1kHz into a 10K ohm load)
Electronically-regulated low and high voltage supplies. Two transformers (toroid for high voltage). Line regulation better than .01%
LS2: (1) 6DJ8/ECC88. LS2 MKII: (1) 6922.
100-135VAC 60Hz (200-270VAC 50/60Hz) 60 watts maximum
Hybrid FET/Tube audio circuit, solid-state power supply
19" (48 cm) W x 5 ¼" (13.4cm) H (standard rack panel) x 10 ¼" (26cm) D. Handles extend 1 ⅝" (4.1cm) forward of front panel. Rear chassis fittings extend ⅞" (2.3cm).
LS2: 13 lbs. (5.9 kg) Net; 21lbs.(9.5 kg) Shipping. LS2B MKII: 14 lbs. (6.0 kg) Net; 22lbs.(10 kg) Shipping.
Our Testing Process for Preamplifiers at SkyFi:
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.
Please click here for detailed specifics regarding our specialized packing process that separates us from the rest.
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