Audio Research D-115 MKII Classic Tube Amplifier

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Here's your chance to own a classic tube amplifier at a reasonable price.

The D-115 MKII delivers 100W using eight 6550 tubes (it actually measured closer to 115W before clipping), while maintaining that traditional warm and precise Audio Research signature sound.

This is a well-built American made unit - not a recent Chinese attempt at HiFi -  weighing in at 68 lbs.

It was made from the highest quality components available at the time, and was hand assembled with care and attention in the Audio Research Minneapolis factory.

SkyFi Service Notes:
• All tubes tested, all tubes that tested weak were replaced.
• Two matched quads of Svetlana 6550 tubes installed. 
• Biased to official ARC service manual specification.
• Front end adjustments also completed to service manual specification.
• Large filter capacitors disconnected and tested for value, ESR, and leakage - PASS.
• Bench tested to rated power plus slightly higher (noted in above description).

Click below to add our recommended matching cables from Kimber Kable, all brand new as SkyFi is an official Kimber dealer.

Kimber Kable - RCA Interconnects

Kimber Kable - Speaker Cables

The SkyFi Testing Process for Tube Amplifiers:
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 tubes are inspected for signs of stress overheating or cracking.

We then power up the unit carefully and run a simple 1k sine wave while monitoring the output on an oscilloscope for signs of distortion or noise. Finally we run the amplifier to its full rated power into the appropriate resistive load provided by our Sencore amplifier tester. If there is an issue, it will usually be noticeable at this point. If it all looks clean we will often test for THD (Total Harmonic Distortion) measured by our Keithley distortion meter, and compare it against the original manufacturers specifications. The amplifier the remains powered on to "burn in" on our test bench for a few hours to make sure there are no heat related issues. If there are balanced inputs available they will also be tested.

We also test all tubes for output gain and leakage on our modern and professional tester against the original manufacturers specifications. If needed, the tubes will be replaced from our vast NOS (New Old Stock) vintage or modern inventory.

Final testing involves pushing actual music thorough the amplifier. We've learned over time that some issues are only noticeable to a trained ear while listening to familiar source material. Our test bench has reference vintage KEF speakers that we're very familiar with which quickly reveal any discrepancies. Some amplifiers will then move into our listening room where they are tested with our in-house reference speakers of choice.

Technical Specifications:
POWER OUTPUT
100 watts per channel minimum continuous power (both channels operating) at 16 ohms from 20Hz to 20kHz with less than 1% total harmonic distortion (typically less than .005% at 1 watt)

POWER BANDWIDTH
D-115 MKII: (-3dB points) 12 Hz to 60 kHz

INPUT SENSITIVITY
D-115 MKII: 0.6V RMS for rated output

INPUT IMPEDANCE
75K ohms, nominal

OUTPUT REGULATION
D-115 MKII: Approximately 0.5 dB, 16 ohm load to open circuit

OVERALL NEGATIVE FEEDBACK
D-115 MKII: 19.5 dB

DAMPING FACTOR
D-115 MKII: Approximately 17

DISTORTION
Intermodulation distortion: Less than .1% at 1dB below rated output (100V p to p, 16 ohms - SMPTE method).

SLEW RATE
15 V/µs

RISE TIME
5 µs

HUM & NOISE
90dB below rated output - less than 2mV RMS - (Broad-bandwidth unweighted, inputs shorted)

POWER SUPPLY ENERGY STORAGE
Approximately 280 joules

POWER REQUIREMENTS
105-125VAC 60Hz 1000 watts maximum, 400 watts at "idle"

TUBE COMPLEMENT
D-115 MKII: (4 matched pairs) 6550, (1) 6550, (1) 12AT7, (3) 6DJ8/ECC88, (4) 6FQ7

DIMENSIONS
19" (48 cm) W (standard rack panel)
7" (18 cm) H
16-1/2" (42 cm) D (front panel back)
Handles extend 1-5/8" (4.1 cm) forward of the front panel

WEIGHT
68 lbs. (31 kg) Net
84 lbs. (38 kg) Shipping