audio research

Solid state stereo power amplifier.



D400 MKII (1993)

From the ARC website

The D200, D300 and D400MKII use similar means to achieve a common goal of musicality at different power levels. In the case of the D200 and D300, the general circuit topology is identical with quantitative differences applying in power-supply energy storage and number of output devices (see specifications for details). The D400MKII, while largely similar in design, also has some features which are uniquely its own.

The D200 and D300 both employ a distributed-capacitor approach to bulk energy storage for the main supply; this means that a number of high-quality electrolytics are linked in parallel to provide the energy reserves necessary to reproduce clean transients and dynamic peaks of accurately-recorded music. This design approach results in lower E.S.R. (a distortion characteristic of capacitors) and lower impedance (quicker delivery of power to the output stage when need ed). The D400MKII, while using larger capacitors for more total energy storage, also incorporates a second power trans- former dedicated solely to supplying the input stage of the amplifier. This approach gives both the input stage and the main supply of the amplifier tremendous dynamic headroom the capability to cleanly deliver power in the face of demanding program material and low- impedance speaker loads.

The D200, D300 and D400MKII all use direct-coupled, high- current Multiple-Emitter Transistors (or METs) in their output stages (as well as for input-stage drivers). These devices have the rugged, high- heat, high-current capability of single emitter bipolar transistors (which can have a rougher, harder sonic character), but they also have a natural sweetness and musicality often associated with MOSFET transistors (which can be more fragile and prone to failure). In short, the METs deliver the best of both worlds. Each of these amplifiers has heat sinking specified to generously handle the dissipation requirements of its respective output stage, allowing safe, convenient in-cabinet installation if desired.

The D200, D300 and D400MKII each have both single-ended and balanced (XLR) input connectors, allowing easy connection to preamplifiers having either type of output. In addition, the D400 MKII offers a second set of inverting single-ended inputs, thereby allowing balanced operation in two different modes. Bridged mono operation, yielding substantially higher power output, is also possible with each of these three amplifiers, in either single-ended or balanced mode. Illustrated bridging instruction are included in the owner's manual for each model.


MSRP (US new retail)
$5,495. Later increased to $5,995. (D400 MKII)


Power output 200 watts per channel into 8 ohms, 400 watts per channel into 4 ohms.
Power bandwidth D400: (-3dB points): 0.01Hz-160kHz
  D400 MKII: (-3dB points) 4Hz to 100 kHz Low level: (-3dB points) 0.01Hz to 160kHz.
Frequency response  
Input sensitivity D400: 1.91V RMS for rated output (26.4 dB gain) unbalanced or balanced
  D400 MKII: 2.0V RMS for rated output (26dB gain) unbalanced or balanced
Input impedance D400: 150K ohms normal or invert, 300K ohms balanced differential
  D400 MKII: 57K ohms normal or invert, 114K ohms balanced differential
Output taps  
Output regulation 0.06dB 8 ohm load to open circuit
Overall negative feedback D400: 9.3dB
  D400 MKII: 9.7dB
Damping factor 150
Slew rate 50V/µs
Rise time 1.0 µs
Hum & noise D400: Less than 150 µV RMS (106dB below rated output IHF A-weighted)
  D400 MKII: Less than 220 µV RMS (105dB below rated output IHF A-weighted)
Power supply energy storage 270,000 µF
Power requirements 105-125VAC 60Hz (210-250VAC 50 Hz) 760 Watts at rated output (200WPC 8 ohms). 1200 watts maximum (400WPC 4 ohms), 220 watts idle
Other Peak output current: 60 Amp peak into 1 ohm
  Input polarity: Non-inverting at normal inputs. Balanced pin 2+
Dimensions 19" (48 cm) W (standard rack panel) x 9" (22.8 cm) (8¾" (22.2 cm) panel + ¼" feet (0.6 cm) H x 17¾" (45.0 cm) D (front panel back). Handles extend 1 and 5/8" (4.1 cm) forward of the front panel. Handles extend 1 and 5/8" (4.1 cm ) behind rear panel
Weight D400: 73 lbs. (33.2 kg) Net, 90 lbs. (41.0 kg) Shipping
  D400 MKII: 76 lbs. (34.5kg) Net, 94 lbs. (42.7 kg) Shipping




D400 MKII: