audio research

Tube stereo power amplifier.

From the ARC website

We are happy to announce the introduction of a new vacuum-tube stereo power amplifier: the VS55, with a rated output of 50 watts per channel. The VS55 makes a wonderful companion to the recently introduced SP16 preamplifier. Together, these exciting new companion products enable you to assemble a true Audio Research music system at a more reasonable cost.

Like the SP16, the VS55 represents a fresh, new design direction for Audio Research. Using an open (rather than fully enclosed) chassis architecture, the VS 55 features a milled, anodized top plate through which the input and output tubes project upward. The chassis is finished in matte black with silver lettering, while the top plate is clear anodized with an inset logo. Behind the tubes and finished top plate are located the output and power transformers and a row of high-quality power-supply capacitors. The appearance is crisp and logical without being overly "retro."

The VS55 ships without a traditional cage-type top cover. An optional perforated cage which covers the tubes is available at additional cost.

Tube locations and types are screened next to each opening in the top plate, along with bias-adjustments for the two matched pair of 6550 EH output tubes. The chassis front has a power switch and LED indicator, while the rear provides gold binding posts labeled 0-4-8 ohms, L and R single-ended inputs, 12V in/out triggers for remote installation and L and R channel access points for a voltmeter (used when setting bias). The amp rests on four elastomer feet and uses a detachable 14-gauge power cord with I.E.C. socket. The virtue of the VS55 is found as much in its logical layout as in its sound: as shipped from the factory, all normal maintenance can be performed without removing a single panel or cover.

Best of all, you will find the sound of the VS55 a delightful complement to any Audio Research preamplifier, especially the SP16. While offering excellent soundstage focus and a vivid, liquid midrange, the VS55 also has surprising musical dynamics. Bass extension and impact are impressive compared to other amflifiers in this power range, thanks to generous power-supply energy reserves and to the efficient output-transformer design. In all, the VS55 bears the sonic hallmarks of being a true Audio Research amflifier: a quick, dynamic and powerful acoustic envelope surrounding an illuminated midrange of palpable lushness and realism. Matched with appropriate, high-quality loudspeakers and source components, the VS55 will give listening pleasure far beyond normal expectations in this price and power range.



In 2007, VS55 had their tubes changed from 6550EH (Electro Harmonix) to 6550C (Svetlana) at the production line. The output tube bias was changed to 55mV, providing better sonics and improved reliability.

Perforated cage-type top cover $200.

MSRP (US new retail)
$2,495. Increased to $2,995 on December 1st 2005.


Power output 50 watts per channel continuous from 20Hz to 20kHz. Approximate actual power available at "clipping" 52 watts (1kHz)
Power bandwidth (-3dB points) 12Hz to 50kHz
Frequency response (-3dB points at 1 watt) 1.0 Hz to 60 kHz
Input sensitivity 1.1V RMS Single-ended for rated output. (25 dB gain into 8 ohms)
Input impedance 100K ohms Single-ended
Output taps 8 ohms, 4 ohms
Output regulation Approximately 1.0 dB 8 ohm load to open circuit
Overall negative feedback 12.5 dB
Damping factor 10
Distortion 1kHz total harmonic distortion typically 1% at 50 watts, below .05% at 1 watt
Slew rate 5 volts/microsecond
Rise time 5 microseconds
Hum & noise Less than 0.2mV RMS - 100dB below rated output (IHF weighted, input shorted)
Power supply energy storage 166 joules
Power requirements 105-125VAC 60Hz (210-250VAC 50Hz) 320 watts at rated output, 500 watts maximum, 200 watts at "idle"
Tube complement (2 matched pairs) 6550EH power output, (3) 6N1P input and driver
Other Tube locations and types are screened next to each opening in the top plate, along with bias-adjustments for the two pair of 6550 Electro-Harmonix output tubes.
The rear has 12 V in/out triggers for remote installation and L / R channel access points for a voltmeter (used when setting bias).
The amp rests on four elastometer feet and use detachable 12 gauge power cord with IEC socket.
Dimensions 14" (35.6 cm) W x 7" (17.8 cm) H x 14" (35.6 cm) D. Rear connectors extend .88" beyond chassis
Weight 32 lbs. (14.5 kg) Net; 38 lbs. (17.3 kg) Shipping.


Issue 142