Audio Research LS25 MKII Tube Stereo Line Stage

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Frequency response ±.5dB, 1.0Hz to 100kHz -3dB pionts below 0.2Hz and 400kHz
Distortion (THD) Less than .01% at 2V RMS output
Noise & hum 14µV RMS residual IHF weighted balanced noise output with gain control at minimum (103dB below 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)
Output polarity  
Maximum inputs 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).
Power supplies Electronically-regulated low and high voltage supplies. Automatic 40 sec. warm-up/brown-out mute. Line regulation better than .01%.
Tube complement LS25: (4) 6922/E88cc dual triode
  LS25 MKII: (2) 6H30 dual triode
Power requirements 100-135VAC 60Hz (200-270VAC 50/60Hz) 45 watts maximum
Other Controls: Volume (104 steps), Gain, Balance, Input. Toggle switches: Power On/Off, Stereo/Mono, Bal In/SE In, Processor/Input, Monitor/Input, Mute/Operate.
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.

This item cannot be ordered online. If you are interested please click on the Ask a Question button below.

The LS25 vacuum tube stereo line preamplifier offers sonic performance, functional flexibility and value second only to the world-renowned Reference One preamplifier. It is unprecedented measured by any performance criteria at its price.

Many will perceive the LS25 as a more compact REF1 -- and to be sure, there are many similarities in the mechanical design. 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 LS25's volume control when used in this mode. Thus, the LS25 fits smoothly into any high-performance installation which combines audio and video playback functions.

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 LS25’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.

Inside, the LS25 is pure Class-A operation Audio Research: gain is supplied via four 6922 twin triodes, with fully regulated massive power supplies and Infinicap coupling caps at the output for maximum dynamics and transparency. Performance is smooth and detailed, with good soundstage focus and plenty of deep bass impact. The overall presentation is refined, yet with power that extends effortlessly into the frequency extremes. Like the REF1, the LS25 never meets a sonic challenge it can’t handle with aplomb -- and it does so while offering all the features needed to fit into today’s multipurpose entertainment systems.


We endeavour to despatch same day for orders placed up to 2pm on available stock items (items with stock message "Usually dispatched within 24 hours"). Please remember to check with us first for a physical stock check if next day delivery is important to you. Any items with stock message "Usually dispatched within 72 hours" are items that we do not hold in stock but order in from the importer or manufacturer as soon as a customer order is recieved. Occasionally these may be delayed beyond 72 hours due to importer/manufacturer stock levels but we will inform you as soon as we can if this is the case.

UK ORDERS:  We despatch the bulk of our UK mainland items on a 24 hour service – Free of Charge.  Non Mainland locations - Isle of Man, Isle of Wight, the Scilly Isles, the Scottish highlands and Islands, the Channel Islands and Northern Ireland may take a day or so longer and are not Free of Charge. Smaller items are delivered using Royal Mail recorded delivery or special delivery. Larger items are delivered using a courier service such as Interlink Express, DPD, UPS or DHL. 

INTERNATIONAL ORDERS: We offer competitive rates which can be confirmed by email. Please just ask – we will need a full delivery address and telephone number. Smaller items are delivered using Royal Mail Small Packets Airmail with International Tracked and/or Signed depending on value of item and availability of the service. Larger International shipments are sent by insured and tracked services using DPD, DHL or UPS. If there are any delays due to specific customs regulations, etc, you will be contacted by Turntableworld or by the courier with a request for any further information required. Customs duties do not apply for shipments into any EU country (for a full list please refer to the EU Country List). Customs duties can apply for countries outside of the EU. Customers in these countries are responsible for all taxes and duties incurred when the items enter their country.

COLLECT IN STORE OR HOME INSTALL:At the request of the manufacturer some items cannot be supplied by mail order but you can click and buy them and then elect to collect them from our store or arrange a home install (if applicable). Applicable items clearly state that they are Collect in store or home install. Once ordered you will receive a message prompting you to contact us by phone or email to arrange for us to deliver and install or to reserve and collect from our store at your convenience, you will also be advised of the delivery time / stock availability as not all Home install / collect in store items are held in stock. 

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