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Reviewer: Srajan Ebaen
Source: Audio Aero Prima SE; Accustic Arts Drive-1
Preamp/Integrated: AUDIOPAX Model 5
Amp: AUDIOPAX Model 88
Speakers: Avantgarde Acoustics Duo; Gallo Acoustics Reference 3; Zu Cable Druid Mk4
Cables: Crystal Cable Reference complete wire set of analog and digital interconnects, speaker cables and power cords; Z-Cable Reference Cyclone power cords on both powerline conditioner; 2 x Stealth Audio Cables Indra analogue & Sextet S/PDIF cable
Stands: 2 x Grand Prix Audio Monaco four-tier
Powerline conditioning: 2 x Walker Audio Velocitor S
Sundry accessories: GPA Formula Carbon/Kevlar shelf for tube amps; GPA Apex footers underneath stand and speakers; Walker Audio SST on all connections; Walker Audio Vivid CD cleaner; Furutech RD-2 CD demagnetizer; WorldPower cryo'd Hubbell and IsoClean wall sockets; Musse Audio resonance dampers on DUO subs
Room size: 30' w x 18' d x 10' h [sloping ceiling] in long-wall setup in one half, with open adjoining living room for a total of ca.1000 squ.ft floor plan and significant 'active' cubic air volume of essentially the entire (small) house
Review component retail: $38,750/pr

Red Rock Audio's massive and expensive 50-watt Renaissance towers with their Class A push- pull 572 power tubes are based on a circuit design by Jack Strayer of Seattle that combined a Williamson front-end with a triode output stage. His participation at VSAC introduced him to Alan Stiefel who had previously distributed KR Audio and Synthesis Audio. Stiefel expressed an interest to work with Strayer and purchased an amplifier. When Strayer's health began to fail, Stiefel formally acquired the rights to his design before Strayer passed away. Gordon Maughan then took over engineering reigns to perfect the amplifier for prime time. As Stiefel tells it, engineer Jack Strayer had been old-school. He didn't believe in the importance of certain parts choices. Alan and Gordon had performed extensive bench tests to know that the basic circuit measured exceedingly well. It was solid. Their subsequent contributions entailed redesigning the front end (Strayer had used 6SN7s), substituting parts elsewhere, optimizing the layout with a multi-story two-sided chassis, increasing power and reducing operational hum levels to inaudibility even with high-efficiency speakers. Jack Elliano of Electraprint custom-designed a new output transformer for them, Bridgeport Magnetics provided their redesigned power supply and the toroids which separate the 830-volt high-voltage supply from the filament supply.

The Renaissance amplifiers are hand-crafted by Gordon Maughan who has worked for Union Pacific Railroad and also designs loudspeakers as a hobbyist. The monoblocks are an AC-filament zero-feedback triode design based on the Russian Svetlana 572-10 which fits between the 811, 211 and 845 and ceased production when the original "pre-wing" company went bankrupt. New Sensor at the time acquired all Svetlana inventories and there is no shortage of 572s which sell for $124/ea. and show/ed up in only a few commercial amplifiers (Wyetech's Topaz and the now discontinued DeHavilland Electra and Aries 572, the Wavac MD-572, Viva Aurora 572 and Cary CAD-572SE come to mind).

As a true Class A design, the Renaissance consumes near equal power at idle and full power: 270 versus 280 watts. Its specified bandwidth is 10Hz to 100kHz and the auto bias adjustments for the direct-heated 572s are performed with the front-mounted meter and its trim pots. The 5-position selector knob connects the meter to each tube in a sequence described in the very comprehensive owner's manual (which even includes circuit diagrams). Bias should be set to 40mA. The auto-biased input voltage gain stage uses a 6BL7 dual triode whose first side is direct-coupled to the second as a cathodyne phase splitter. These two phases feed a second self-biased 6BX7 voltage gain stage that is capacitively coupled to the four 572 output tubes.

Separate capacitor-coupled Pi filters with customized toroidal chokes isolate the predriver/driver stage and the output stage and further RC networking is employed. Except for the bottom-mounted power supply circuit board with the soft-start circuit and AC mains filtering, the Renaissance is point-to-point wired, often with turret-style posts. To avoid thermal shock for the 572s on both power-up and power-down, the filament and bias supply voltage step up over 30 seconds before a 2-minute delay applies the high voltage. Convection cooling for the tubes uses a rear air intake screened with wire mesh. A covered rear panel bay hides access to four hum pot adjusters and the output tube protection fuses. The 100 lbs chassis uses 1/8", 3/16" and 3/8" aluminum and the wooden dress wings on the front can be easily changed to accommodate a variety of decor options.

Alan and Gordon claim that their amplifier is stable even into more reactive and challenging loads like Soundlabs of which Alan owns a mid-sized older pair. The limitation of this amplifier is simply raw power. 50 watts mandates speaker sensitivities of >88dB, this naturally always subject to room size, listening levels and your ideas of dynamic headroom and bass control.

Red Rock Audio paired this amplifier with ESP Concert Grands at the Rocky Mountain Audio Fest 2004, an event Alan Stiefel jointly organized with Ron Welborne and the Colorado Audiophile Society. I subsequently missed the Red Rock Audio exhibit at T.H.E. Show 2005 where the Renaissance monos were teamed up with their friend's prototype dynamic line source array. To test the amps in Arroyo Seco, I'd first use my 103dB Avantgarde Duos to get a fix on general sonics in my customary setup. I'd then substitute Anthony Gallo's petite-but-potent References 3s. Their
88dB load and passive sealed bass alignment with that high-excursion 10" side-firing woofer presents something far more typical in category -- if certainly not price -- to what one expects a prospective Renaissance amp owner would likely use.

Because the Svetlana website no longer exists, I've included their original spec sheet for the 572-10 for those interested. Four different variants of the 572 exist, distinguished by the number following the 3-digit group designation(3, 10, 30 or 160). The Red Rock Audio Renaissance uses the SV572-10.