audio research

Solid state stereo power amplifier.

From the ARC website

The SD135 is an entirely new amplifier for Audio Research involving a new mix of discrete devices within the framework of a pure analog, solid-state design.

Like the larger HD220, the new SD135 ("SD" for "Silicon Drive") uses Thermal Trak® self-biasing output devices in a Class A-B design. And like the HD220, it accommodates either single-ended or balanced inputs. But unlike the larger hybrid, the SD135 features an all-solid-state input stage using multiple JFET devices in each channel, directly driving the output stage – no interstage coupling capacitors needed. Because expensive coupling capacitors and high voltage regulated supplies required in tube circuits can be omitted, the SD135 is within reach of many more music-lovers.

The SD135 is an amplifier with amazingly fast response time, explosive dynamics and plenty of current delivery for a wide range of speaker types including difficult, low impedance models. Frequency response is an amazing 0.4Hz to 300kHz! Bass is deep, controlled and quick to the punch. The noise floor of the SD135 is extremely low, rendering micro-dynamics and subtle sonic nuances with vivid clarity against a black background. Its presentation is transparent, detailed, and grainless – no listener fatigue here. Pair it with an Audio Research preamp and you will hear an immense soundstage in a highly refined and purely musical presentation.

Reassuringly, the SD135 features protection circuitry that is sonically invisible. If there is DC at its inputs, or if its outputs are shorted, the SD135 will go into protect mode, muting the output and protecting your valuable loudspeakers.

A low-speed (and quiet) 12V D.C. fan cools each channel's internal heat sinks, helping to insure long, trouble-free life. The detachable power cord is a high quality IEC-type rated for 20 amps. The anodized front-panel is available with a natural or a black finish. Front panel handles are included but may be easily removed if the installation demands it.

The SD135 provides the Audio Research hallmarks of high definition® and musicality in a compact, affordable package that will simply eclipse the competition. You must audition the SD135 for yourself to hear the latest evolutionary step in solid-state technology.





MSRP (US new retail)


Power output 130 watts per channel into 8 ohms from 20Hz to 20kHz. 230 watts per channel into 4 ohms.
Power bandwidth  
Frequency response (-3dB points at 1 watt) 0.4Hz to 300 kHz
Input sensitivity 3.2V RMS BAL for rated output. (20 dB Bal gain into 8 ohms)
Input impedance 300K ohms Balanced, 150k ohms SE
Output taps  
Output regulation Approximately 0.05dB 8 ohm load to open circuit
Overall negative feedback  
Damping factor Approximately 170
Slew rate  
Rise time  
Hum & noise Less than 0.05mV RMS -116dB below rated output (IHF weighted, input shorted).
Power supply energy storage  
Power requirements 105-125VAC 60Hz (210-250VAC 50 Hz) 500 watts at rated output (130 WPC 8 ohms) 600 watts max, 150 watts idle.

Output polarity: Non-inverting. Balanced input pin 2+ (IEC-268).
Output current: 60 Amps Peak (1 millisecond)

Dimensions 19" (48.3 cm) W x 6.25" (15.9 cm) H x 15" (38.1 cm) D. Handles extend 1.5" (3.8 cm) forward.
Weight 42.8 lbs. (19.5 kg) Net; 55.3 lbs. (25.2 kg) Shipping.