General:The D52 Amplifier From Audio Research is a formidable solid state amplifier quite capable of driving just most vintage speakers. It would be a perfect match with the Audio Research SP6B tube preamp we have listed. The D52 gives you the sound you expect from an Audio Research amplifier without the super high entry price of some other models. This particular example has also been super well cared for by the single previous owner. When tested at our bench, both channels cleanly made 50W of power into 8 ohms. This is exactly what it was rated for over 45 years ago!Included with the amp will be its original manual, box, and some spare fuses.SkyFi Cosmetic Notes:Some scratches on the sides. Faceplate is super clean. Overall very good condition.SkyFi Technical Notes:This amplifier received a bit of light servicing while here at SkyFi. We replaced all four front panel fuse holders and tightened all of the rear panel connections. A set of spare fuses is included with the unit.Brand Background:Audio Research continues its dedication to unparalleled musical expression and crafting components of the highest quality and lasting value for its customers. Our long-term dedication to service is peerless in this industry (Audio Research, with few exceptions, can repair anything ever produced during its entire history). We continue to seek out new and exciting ways to make music more real and more enjoyable. More than just a name or a marketing tool, Audio Research has come to represent exceptional performance and long-term value. Experience Audio Research – experience High Definition®.Ownership:Single OwnerConnections:RCA Inputs, Speaker Binding Posts.General Sound:Smooth, uncolored, undistorted natural and cleanWorking Condition:Working perfectly and tested in our lab and listening room.Included:Unit, Box, ManualPacking:Original Manufacturers PackingSpecs:Power output: 50 watts per channel into 8Ω (stereo)Frequency response: 0.05Hz to 100kHzTotal harmonic distortion: 0.25%Damping factor: 500Input sensitivity: 1.1VSignal to noise ratio: 90dBSpeaker load impedance: 4Ω to 16ΩDimensions:18.90 x 5.12 x 10.51 inWeight:39 lbs.Approximate Age:1978Link to Manual:Click HereRecommended Cables:Kimber Kable - RCA Interconnects - BetterKimber Kable - RCA Interconnects - BestKimber Kable - Speaker Cables - BetterTesting Process:We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect the PCBs for discoloration from resistors or transistors that may have been running hot. On vintage units we often spot check select capacitors for value and ESR.If the amplifier passes visual inspection, we move on to a controlled power on sequence using a Sencore safety analyzer to monitor current draw in real time. Once the amplifier is determined to be safe to operate, we connect it to full AC mains for function and power testing. We connect the speaker outputs of the amplifier to a Sencore PA81 Power Analyzer which acts as a dummy load, DC offset monitor, and oscilloscope interface. We start with a low level 1 KHz test signal at the amplifier's input and slowly increase its amplitude while monitoring the output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping. At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance. If the device under test has both balanced and single ended inputs they are both tested at this time.We finish off the bench evaluation with a 1 KHz square wave check and a 20 Hz to 20 KHz sine sweep to assess the amplifier's frequency response characteristics. This battery of tests will usually reveal if the amplifier has any issues that need further attention.Before the device leaves the bench, we perform a listening test with actual music using a variety of preferred test tracks. Our benches are outfitted with familiar monitor speakers which help us identify inconsistencies that will not always show up on our test gear. The main things that we are listening for are hum or noise with no signal present, proper center image, clicks, pops, or any other obvious undesirable audio characteristics.If the unit passes all of these tests it is moved to our long term testing rig where we simulate real word operating conditions for 6-8 hours minimum. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when the unit has fully come up to temperature.
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