Control Functions: Volume, Gain Set, Balance, Input Select, Power On/Off, Stereo/Mono, BAL/SE, Processor/Input, Monitor/Output, Operate/Mute.
Inputs: SE / BAL Tuner, Phono, CD, Video, Aux 1, Aux 2, Monitor, Processor.
Outputs: SE / BAL Record Out, Main 1, Main 2.
Frequency Response: +/-.5DB, 1.0Hz to 100kHz -3dB pionts below 0.2Hz and 400kHz.
Distortion: Less then .01% at 2V RMS output.
Gain: Main Output: Selectable for each input: 18db, 12dB, 6dB Balanced output. (12dB, 6dB, 0dB SE output).
Record output: 0dB.
Input Impedance: 120K ohms Balanced, 60K ohms SE.
Inputs (8): Tuner, Phono, CD, Video, Aux 1, Aux 2, Monitor, Processor (XLR and RCA connectors).
Output Impedance: 650 ohms Balanced, 325 ohms SE Main (2), 20K ohms minimum load and 2000pF maximum capacitance. Outputs (3: 2 Main, 1 Record (XLR and RCA connectors).
Maximum Input: 28V maximum, BAL, 14V maximum SE (6dB gain) .
Rated Outputs: 2V RMS 1Hz to 100kHz into 200K ohm balanced load (maximum balanced output capability is 40V RMS at less than 0.5% THD at 1kHz).
Controls: Volume (104 steps), Gain, Balance, Input.
Toggle switches: Power On/Off, Stereo/Mono, Bal In/SE In, Processor/Input, Monitor/Input, Mute/Operate.
Power Supplies: Electronically-regulated low and high voltage supplies. Automatic 40 sec. warm-up/brown-out mute. Line regulation better than .01%.
Noise: 14uV RMS residual IHF weighted balanced noise output with gain control at minimum (103dB below 2V RMS output).
Tube Complement: (2)-6H30 dual triode. (Vacuum tube audio circuit, solidstate power supply.)
Power Requirements: 100-135VAC 60Hz (200-270VAC 50/60Hz)45 watts maximum.
Dimensions: 19" (48 cm) W x 5.25" (13.4 cm) H (standard rack panel) x 11.75" (29.8 cm) D Handles extend 1.50" (3.8 cm) forward of front panel.
Weight: 18 lbs. (8.2 kg) Net; 28 lbs. (12.7 kg) Shipping..
Valve line stage preamp remote control, SE-I/O, Bal-I/O
The LS25 MKII vacuum tube stereo line preamplifier offers sonic performance, functional flexibility and value second only to the world-renowned Reference One preamplifier. Chassis construction is like the REF1, with finished slab sides and heavy top and bottom covers; chassis height and depth are slightly reduced, however. Front-panel control layout is also familiar: microprocessor-controlled rotary devices are used for overall gain set (High, Medium and Low), volume, balance and input selection. Two-way toggle switches control Power On / Off, Stereo / Mono, BAL / SE, Processor / Input, Monitor / Input and Mute.The selectable overall gain function allows a wider range of volume-control operation for input sources having different output levels (for example: a phono stage vs. a high-output D/A converter). The A-V processor to control overall system volume level instead of the LS25MKII's volume control when used in this mode. The rear panel offers a full complement of audiophile-grade balanced and single-ended connectors: seven inputs (including tape monitor), a tape / record out and two sets of main outputs. Balanced or single-ended optimization for every input is selected via the front-panel toggle, and is automatically remembered (along with previously selected gain level) by the LS25MKIIÂÂÂÂÂ’s internal memory. All functions (except gain and SE / BAL) are addressable via the supplied handheld IR remote control. A.C. power is supplied at the rear panel via a three-pin IEC socket and 14-gauge detachable power cord. The LS25MKII has proved highly popular for both its musicality and its many features and system flexibility. With recent engineering breakthroughs at Audio Research, however - especially stemming from the devlopment of the VTM200 input stage technology-it became increasingly clear that the venerable LS25 was the perfect preamplifier candidate for these latest performances enhancements. Because it already has so many useful control functions, the LS25MKll remains almost entirely unchanged in its exterior configuration-meaning original units can be updated at the factory to the MKll spec, Inside however, you will find a new motherboard architecture that incorporates a JFET input stage similar to that used in the VTM200, followed by a cathode-follower/outputdriver stage usuing two 6H30 twin triodes. The 6H30 is a new tube for Audio Research ideally suited to its function in the LS25MKll. It is a Russian military tube in current production and use, and is rated by its manufacturer to have an estimated service life of 10,000 hours.It has shown highly stable and consistent in its operating charecteristics. While its pin configuration is similar to the 6922, it is not a direct replacement. It has higher current requirements for the heater filaments, so it requires a different power transformer than used in the original LS25, as well as power supply adjustments. Finally, like the VTM200, the LS25 MKII also incorporates a rea-panel 12v on/off trigger for even easier incorporation into audio-video installations, or simply for installations where the customer wants more convenient system control. This is the only external modification to the original. You will see this feature appear on future models from Audio Research as well.
