audio research
DUAL 400

Three chassis tube stereo power amplifier.

This was a development model only but was too expensive to build and physically too large to make it a viable product. Instead of releasing the Dual 400, ARC used a lot of the design features from the Dual 400 and released the legendary D-150 amplifier instead.

There was a newsletter sent out with the following contents:

April 10, 1973

News letter 

Subject: Dual 400 Amplifier


This newsletter is provided in advance of product availability to answer
information requests.

The Dual 400 amplifier will be the largest and most powerful in our
series of high definition vacuum tube amplifiers.

Construction will be again near military quality, featuring all anodized
aluminum chassis, panels, cover, etc.  Our normal extremely conservative
component usage is again employed, as is our patented circuitry.

Three chassis are used, with weight totaling 200 pounds. Rack panels
with handles will be standard equipment, as will built in fans and

The power supply chassis is equipped with an eleven position switch
allowing operation from 105 to 125 and 210 and 250 volts AC at either 50
or 60 hz. This chassis is also equipped with a meter so that line
voltage (as well as proper operating voltage) may be monitored.

Each of the two amplifier chassis is equipped with a pair of fans: one
under each group of four (6550) output tubes. Additionally, a meter is
provided to monitor power on 4, 8, and 16 ohms, as well as to allow
individual output tube bias adjustment.

This amplifier will be capable of providing approximately 400 watts RMS
per channel at 4, 8, or 16 ohms into complex loads.  If continuous
commercial service full power sine wave operation applications are
contemplated, an additional power chassis should be used.  (One is
adequate for music and speech applications.)

A word of caution for any possibly home fidelity users: this unit idles
at approximately 1000 watts of power input and heat output,  so give due
consideration to both power-line current requirements as well as
anticipated environment temperature rise.

The unit will also be available with only one amplifier chassis for
monaural (single channel) operation, identified as the M-400.  Prices
are projected as follows:

                    D-400         $2,950.00     

                    M-400         $1,950.00 

                    D-400C        $3,950.00   (commercial version, extra power chassis)

April 10, 1973

Audio Research Corporation

Preliminary Specifications


Dual 400 Amplifier  (and M400 amplifier)


Power bandwidth:          15 Hz to 30 kHz


Harmonic Distortion:      Less than .1% at midband at rated power

                          Less than .25% at 30 Hz at rated power

                          (distortion also reduces as power decreases)


IM Distortion:            Less than .5% at rated power (60 Hz and 6kHz, 4:1)

                          Less than .01% at 1 watt


Sensitivity:              1.5 V RMS for rated power


Output Impedances:        4, 8, 16 ohms


Prices:                   D-400            $2,950.00

                          M-400            $1,950.00

                          D-400C           $3,950.00   (commercial version)


Availability:             October 1973


All performance figures are based on continuous sine-wave and both channels operating. 

Shipments will start in October 1973.

The amplifier has been mentioned in the following magazines:

- Audio Amateur, 3/75 (USA)

- Radio&Television, Nr.3 1974 (Sweden)





MSRP (US new retail)


Power output 400 watts per channel
Power bandwidth 15 Hz to 30 kHz
Frequency response
Input sensitivity 1.5 V RMS for rated power
Input impedance  
Output taps 4, 8, 16 ohms
Output regulation  
Overall negative feedback  
Damping factor  
Distortion Harmonic Distortion: Less than .1% at midband at rated power. Less than .25% at 30 Hz at rated power.
IM Distortion: Less than .5% at rated power (60 Hz and 6kHz, 4:1). Less than .01% at 1 watt
Slew rate  
Rise time  
Hum & noise  
Power supply energy storage  
Power requirements 105-125, 210-250 VAC 50-60 Hz
Tube complement (4 matched pairs) 6550 per channel
Weight 200 lbs.