audio research

Tube mono power amplifier.

From the ARC website

Using all vacuum-tube input and driver stage circuitry in conjunction with 16 type 6550C output tubes, each amplifier puts out up to 600 watts of wide-bandwidth (12 Hz to 80 kHz) power into speaker impedances of one to 16 ohms. Measured frequency response (-3 dB points) is 2 Hz to 200 kHz. Main power supply energy storage is rated at 669 joules. Output terminals are proprietary gold-plated 5-way binding posts. Each output tube is individually biasable from the front panel. Illuminated meters provide A. C. monitoring, real-time power output and tube biasing data. Variable control of meter illumination and internal cooling-fan speed is standard. A standby mode limits tube current draw during warmup or between periods of operation. Front panels of both Reference Series models are available in anodized natural aluminum or black at no extra cost.




From the ARC website

There is good news for REFERENCE 600 owners. The same sonic improvements found in the new REF300 can be obtained in a Mark II Factory Update program for the REF600. Original REF600 units are literally taken apart and painstakingly rebuilt with new output circuit boards and new input / regulator board, using all-new components. The rear panel is also retrofitted with a new three-pin, 20-amp A.C. connector and detachable cord.

At the same time, the convenience and flexibility of the original REF600 has been preserved. Front-panel controls and large, illuminated analog meters allow easy output-tube biasing, A.C. line voltage monitoring, and power-output observation. Using all vacuum-tube input and driver circuitry (6922 twin triodes), as well as tube regulation, each REF600 MKII employs eight matched pair of type 6550-C output tubes to yield well over 500 watts of wide-bandwidth power into speaker impedances ranging from 1 to 16 ohms. Main power supply energy storage is rated at 669 joules. Output terminals are proprietary gold-plated 5-way binding posts.

Suggested U.S. retail for the MKII Factory Update is $7495 per pair. New vacuum tubes and shipping to / from factory are extra. For those music lovers who require the ultimate in power delivery, new-build REFERENCE 600 MKII amplifiers are available at U.S. $17,495 each, or $34,990 the pair, suggested retail.

The sonic advance represented by the new MKII is impossible to describe in a manner commensurate with the experience of actually hearing them at length in a relaxed audition.


From the ARC website

Following upon the technical changes that have been so successfully received in the MKII version of the REF300 monoblocks, similar changes have now been made to the design of the REF600 model. The resulting improvement in sonic performance is, if anything, even more dramatic in the 600-watt flagship model.

As in the REF300, the REF600MKIII has been refitted with new audio and power-supply circuit boards incorporating 6N1P triodes for initial gain and excellent dynamics at this critical signal level. Dual-triode 6H30 tubes are used as drivers for the output stage (one 6H30 per pair of 6550C output tubes). This proven, reliable combination is further refined by the extensive application of teflon capacitors in the audio path.

The resulting sonic improvement is as musically significant as it is impressive. Never before have we heard such ease of delivery and absence of electronic artifacts from any amplifier in our sound rooms. Three-dimensional focus and image palpability are the most dramatic we've encountered. Bass extension, impact and control give immense weight to spectacular recordings like the GLADIATOR soundtrack - these amps are simply unflappable! Once again, these great monoblocks reign supreme: there is simply nothing else that comes close to the performance of the REF600MKIII.

Operational features are identical to the previous MKII version, with one minor addition. A 12V trigger mechanism has been added to allow for remote installation power on/off. The front-panel setup for monitoring and biasing output tubes remains unchanged.

Factory upgrades from MKI or MKII versions are now available; new small-signal tubes and power supply tubes are included in the update price, but new output tubes are additional cost as necessary. Freight to and from the factory are the responsibility of the customer.

For the customer who appreciates the very best we can offer in a power amplifier, the REF600MKIII meets every sonic expectation - and then some.


MSRP (US new retail)
$29,990/pair (REFERENCE 600)
$34,990/pair, later increased to $39,990/pair (REFERENCE 600 MKII)
$39,990/pair (REFERENCE 600 MKIII)


Power output 500 watts continuous at 16 ohms from 20Hz to 20kHz with less than 1% total harmonic distortion (typically less than .05% at 1 watt). Typical power under average circumstances will be around 550 watts. Maximum power under ideal conditions will be around 600 watts.
Power bandwidth (-3dB points) 12Hz to 80kHz
Frequency response (-3dB points at 1 watt) 2Hz to 200 kHz
Input sensitivity 2.0V RMS balanced for rated output
Input impedance 200K ohms balanced
Output taps  
Output regulation Approximately 0.5dB 16 ohm load to open circuit
Overall negative feedback 12 dB
Damping factor 16
Slew rate  
Rise time  
Hum & noise  
Power supply energy storage  
Power requirements 105–125VAC 60Hz (210–250VAC 50Hz) 1600 watts at rated output, 2200 watts maximum, 800 watts at idle, 300 watts standby
Tube complement REFERENCE 600: (8 matched pairs) 6550C power output; (4) 6550C regulators; (2) 7233 regulators; (2) 6922 regulator amplifier; (8)12AX7 driver; (2) 6922 input.
  REFERENCE 600 MK II: (8 matched pairs) 6550C power output, (4) 6550C regulators, (3) 6922 regulators, (8) 6922 driver; (2) 6922 input.
  REFERENCE 600 MKIII: (8 matched pairs) 6550C power output, (4) 6550C regulators, (3) 6N1P input/follower, (8) 6H30 driver
  The REFERENCE 600 has sufficient bias adjustment range to allow the use of any of the following output tube types: 6550, 6550B, 6550C, KT88, KT90, KT91, KT100.
Dimensions 19" (48.3 cm) W x 10.5" (26.7 cm) H x 29.5" (74.9 cm) D. Handles extend 1.5" (3.8 cm) forward
Weight 170 lbs. (77.2 kg) Net; Shipped in pairs, 495 lbs. (225 kg) per pair


Issue 121 (REFERENCE 600 MKII)