When released, Audio Research’s SP11 was their flagship, 2-chassis preamplifier. It garnered praise for its exceptional ability to reveal musical passages with haunting realness. This is partly due to its being extremely silent in operation. This is a beautiful foundation of a hi-end vintage system. Both units were serviced and all controls cleaned by our veteran amplifier tech. The phono stage is also excellent and allows for a nice range of loading for a variety of cartridges. I particularly enjoyed this statement in a review in Stereophile, First, it must be said that the SP-11, more even than most other preamps, does not like a cold start. After 15 minutes warmup, it sounds very good. After an hour it starts to pull ahead, sonically, of any of its known competition. After two hours, it is head and shoulders better than anything I have ever heard! SP11 / SP11PS FEATURES -Hybrid stereo preamplifier with phono stagePower supply in seperate chassis for silent operationSelectable phono loadingSelectable filtersPrecision Japaneese attenuator and selector potsDirect Mode PREAMPLIFIER SPECIFICATIONS -CLASS - Hybrid Stereo w/ (6) 6DJ8 TubesFREQUENCY RESPONSE - 0.2Hz to 100kHzHARMONIC DISTORTION - Less than 0.005%NOISE AND HUM - 110dBINPUT IMPEDANCE - Phono selectable 47k, 100, 30, 10, 3 OhmsOTHER FEATURES - Filter: 25Hz Hi-pass phono subsonic 6dB/octave rolloff (to eliminate ringing) with transition to 12dB/octave at 10Hz. Front panel switchable phono only. Controls (6): Gain, Level (to set gain range), Balance, Mode, Input, Impedance. Switches (8): Tape monitor, Copy, Tape 1/2, Tape 1to2 / 2to1, Mute, Invert phase, Bypass, Filter.OUTPUT IMPEDANCE - 250 Ohms MainDIMENSIONS - (LxWxH) 10.25 x 19 x 5.25 - SP11PS is the same sizeWEIGHT: 29 lbs (with power supply) IN THE BOX -SP 11 PreamplifierSP11PS Power SupplyPower and power supply connection cables CONDITION - All pieces were well cared for by the original owner and are clean and dust free. No sign of smoke, pets or kids. Both faces are scratch free and amazingly there are no dings on the corners or edges..a rare find. SHIPPING - We ship worldwide with UPS, Fed-Ex and various truck freight lines. All items are packed and padded with care if the original packaging is deemed insufficient. We know how exciting it is to anticipate the arrival of new gear and we want your item to arrive in the same condition it left our facility.