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Red Rock Audio Renaissance Monoblock Amplifier Review

Constantine Soo re-assesses the state-of-vacuum-tube-amplifier-art via the Red Rock Audio Renaissance monoblock power amplifiers with Svetlana SV572-10 output tubes

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Red Rock Audio Renaissance Monoblock Amplifier

Red Rock Audio was founded in 1994, after a chance meeting between Al Stiefel and Gordon Maughan at the Colorado Audiophile Society that cemented the foundation of the company. At that time, Al was investigating the prospect of cable manufacturing and Gordon was passionate in cable constructions, especially the application of graphite in Teflon tubing, a very labor intensive process. They teamed up to offer their cable designs to the local market, and were met with relative success.

Red Rock also had limited success in importing products from KR Audio and Synthesis, which prompted the company to consider designing and manufacturing its own amplification products. The pivotal moment came in 1998 when Gordon met the late Jack Strayer of Audio Technical Products at the Washington VSAC.

Gordon was fascinated by Jack’s amplification prototype that was designed around a classic Williamson circuit, with the anode input gain stage directly coupled to a cathodyne phase splitter and then capacitively coupled to another gain/driver stage. According to a recount by Gordon:

“Using the 6SN7 octal tubes, Jack’s amp had too much gain since the original Williamson design included the use of global feedback to stabilize the pentode outputs and to reduce output impedance. I simply chose lower-gain octal dual triodes to reduce the overall gain. Also, the octals chosen are personal favorite of a few friends since the tubes are very stable and linear with good drive, and they are available in NOS with very good sound capabilities without being expensive. They are the 6BL7 and the 6BX7, with the latter having less gain but more plate dissipation and lower impedance, thus it is used as the driver tube for the outputs tubes.

What this achieved was a very stable, reliable circuit and a gain that is close to industry standard with 1 volt RMS, achieving close to full output power. Of great importance for dynamic quality is the use of active bias for the output stage. This eliminates all regenerative feedback at the output stage and gives better transient snap and dynamics that more closely track the original signal. Self bias is simply regenerative feedback to reduce gain and to lower impedance; it is negative feedback only limited to a single stage. All negative feedback costs in the ultimate potential of the amp’s ability to track the original in terms of phase/time and dynamics. The cost of active bias on this design is the need to adjust manually and the added circuitry. With the stability of the Svetlana 572’s, we have found that once bias is set, it rarely needs adjustment, plus the design affords easy adjustment and measuring of bias from the front panel.”

With the new, unique design concept, the team worked towards creating an ultimate amplifier that would offer the following: 1. provide world-class audio performance when used in a high-caliber system; 2. to be complimentary to living-room décor; 3. to sport rock-solid operational reliability through conservative engineering. The end result was a tube monoblock amplifier capable of reproducing a bandwidth of 10 to 100,000Hz minus 1.5dB at 10Hz, minus 1.1dB near 60kHz, minus 1.6dB at 100kHz, and ruler-flat from 100Hz to beyond 20kHz. See the scanned chart below from the Owner’s Manual.

The THD+N figures are no less impressive:

In 2003, right before the death of Jack Strayer, Al met him in person for the first time, and subsequently completed the first full pre-production prototype in the following year. According to Al, the JS design accorded a time advantage to Red Rock, although the actual tube compliments and transformer type were completely re-designed:

“His amp was very similar to what we were developing so we decided to use it as the basis of our development; it took us four years to get our product finished. There is very little left of the original design except the primary circuit is similar (Williamson). We decided to refine a Push-Pull topology since most single-ended designs have limitations in band width and have very pleasant tonality at the expense of accuracy. There are some very powerful pentode push-pull amps that are cable of driving less efficient speakers but we believe they have sacrificed the finesse and tonal accuracy of a world class direct heated triode (DHT).”

The Tall Tube Amplifier

Aside from the fact that Red Rock Renaissance is of the very rare breed of tube amplification that sports unusual, impressive specs, the other aspect about the monoblock amplifier that represents a greater shock factor is its physique: The Renaissance is only a little over 9 inches wide, and yet it measures over 17 inches deep and stands erect at over two feet tall, making it the tallest tube amplifier in existence.

The physical, upright construct of the Renaissance stemmed from design priorities that emphasized performance, such as optimal thermal cooling, efficient inter-connectivity and ease of assembly and servicing, and it is thus built from bottom up like a building. In the first stage of implementation, being the sector that generates the most electromagnetic noise, all components that perform the very crucial AC power management and preliminary AC filtering are anchored at the bottom of the chassis, physically away from actual gain stages.

Transformers are then secured on one side of a central support that splits the chassis’s internal volume in a 70% volume, with the other 30% of space on the other side filled by shared through-mount bolts and chokes. The central support is a 3/16-inch thick aluminum plate that provides the triple functions of electromagnetic isolation between the transformers, mounting of the transformers and chokes directly above the AC power management for the shortest connection, and locking the chassis together.

Energy storage capacitors for the rectification and filtering of transformers’ output are mounted directly above the HV transformer, an ingenious layout that serves to minimize component inter-connectivity. On the HV power supply transformer, Gordon offers the following:

“The HV power supply transformer also uses a center tap which gives us ½ the total output voltage which is used for the driver stages and the total voltage for the output tubes. One choke is for the output tube power supply and the other choke is for the driver stage power supply. This further isolates the two supplies and also increases the noise rejection and energy storage of these supplies.

The other transformer supplies AC filament supplies for the output tubes, the bias supply voltage and the filament supply which is rectified to DC for the driver stage tubes. Having these functions contained in this transformer allows the AC power management to ramp up the voltage to this transformer, reducing thermal shock to the filaments, allowing the tubes to heat near operating temperature before HV is turned on. During turn off, the HV disconnects first and then the filaments turn off, further increasing the expected tube life.

Above the filament/bias supply transformer, the central support ends to allow the output transformer to mount directly to the rear panel with the HV input side windings placed directly under the output tubes, and its output windings connected to the speaker/output binding post directly under the transformer. Again minimizing interconnection points between components yet increasing electromagnetic isolation between components.

Regarding electromagnetic noise inside the chassis, the most isolated area is directly under the driver stages at the top front of the chassis, where most of the voltage gain occurs. Finally all components can be accessed by simply removing the 1/2″ thick side panels, making servicing easy.”

Output Tube

The Renaissance is also unusual in tube amplification for its directly-heated triode tubes driven in a push-pull topology, as well as using four Svetlana 572 power tubes to generate a total output of 50 watts per channel. The Renaissance Owner’s Manual outlined the option of using either the Svetlana 811-10’s or 572-10’s on the amplifier; however, in a Dr. David Kirkby’s G8WRB website reside complete factory data sheets on Svetlana tubes, among them a beautiful Svetlana SV572-10 pdf document titled, Svetlana Technical Data SV572-10 High Performance Audio Power Triode, which lists attributes of the SV572-10 that attests to its ideal role in high-end audio:

Massive graphite anode for high power capability, 125 Watt rating
Directly heated thoriated tungsten filament for soft glow and warm sound
Transmitting tube design, hard glass envelope with white ceramic base
Low microphonic construction with ceramic internal spacers and mica supports
Excellent gettering enhanced by titanium bonded with the graphite anode surface
Titanium has an idex of gas absorption 10 times greater than barium
Superb aesthetic appearance

But, of utmost importance to the audiophile is the following final bulletin point:

“The SV572-10 delivers performance and sound superior to 100-watt triodes, such as the antique 211 or 845. The SV572-10 has lower plate resistance, lower filament power and smaller physical size.”

By comparison, the Svetlana SV811-10 Low-Mu Power Triode pdf document lists the following attributes of the tube:

Directly heated thoriated tungsten filament for soft glow and warm sound
Hard glass envelope with white ceramic base
Low microphonic internal construction
Titanium gettering system
Tri-plate anode
Superb aesthetic appearance

Svetlana.com lists each 572-10 in a matched pair for $156 ($312 per pair, $624 for one Renaissance), while the SV811-10 lists for $108 each in a matched pair. Cary and deHavilland are two other audiophile brands that have also created designs based on the 572.

Al and Gordon considered today’s triodes as the most ideal amplification devices for its superior gain linearity over other tubes, and the fact that the Svetlana SV572-10 also features a directly heated thoriated tungsten filament “for slow glow and warm sound” makes it a glistering candidate. As the temperature of the cathode of such tubes reaches 2000̊F, the extreme density of electron cloud created by thermionic emission becomes much higher than those created by indirectly heated triodes, which augments signal transfer potentials from the gain device.

Power Supply

The design of the output transformer was customized by Jack Eliano of Electra-Print, being given the very specific design parameters of a parallel push/pull circuit topology, a 20-to-40kHz bandwidth, a 100-watt-plus power handling capacity with at least 1.2kV voltage capability.

The end result was a class-A design with 50 watts of output from one of the largest system of power supply components available, and yet will not overload any part of the circuit or gain devices. With the utilization of capacitors specified at 1KV and the actual supply voltage of 830 volts harnessed within an operational safety margin, 50 watts of output was thus obtained from the power supply rail voltage. Gordon has more on the capacitors used:

“The caps that were chosen are some of the best I’ve measured when it comes to quality factor, dielectric absorption, cost and size. One of the reasons we believe this amp performs so well is the storage and quality of the power supply. If we chose to have, for example, a 1.2KV supply (about the max limit of the Svetlana 572s) the capacitors alone would have consumed at least 2 times the volume with similar capacitance, quality factor, and low dielectric absorption. I would still want similar capacitance even with the increased voltage although Joules of energy would be increased, the impedance of the supply is still of concern regarding quality of sound. The power supply transformer and chokes would also have increased in volume and weight by at least 30%. The amps currently are near the size limit that I can still maneuver by myself for construction and set up.”

Bias & Output

The Renaissance has only one power switch and it is located on the front panel. The start up sequence is a 2-minute process that first increases voltage gradually to the tube filaments and bias supplies in the first 15 seconds, then turns on the high voltage to the warmed tubes afterwards. While the voltage bias of input and driver tubes are self-adjusted, the quad of SV572-10’s are manually biased to the 40 milliamps setting via the four potentiometers on the front panel beneath the meter.

At the optimal bias level, the Owner’s Manual specifies a pure class-A output of 40 watts over extended bandwidth, which will increase to 50 watts class-A albeit with higher distortions. The Owner’s Manual warns of shortened tube life in over-bias and reduced dynamics in under-bias.

Bias level check became a fun routine for me each time the Renaissance was turned on, and adjustment was via a supplied small screwdriver. Red Rock Audio provided this plastic screwdriver as a precautionary measure against having its customer using his own metal screwdriver and scratching the front panel during use. The experience of using the Renaissance has made operations of other amplifiers less fun. That said, performing the bias adjustment in the extremely straightforward and user-friendly layout of the Renaissance is about as far as I am willing to go in manual operations of anything audio.

Because of the excessive current channeling constantly through the SV572-10’s, Red Rock Audio recommends lowering the bias by a counter-clockwise one-quarter turn before changing tubes, and raising the bias back to optimal after the new tube is inserted securely.

Auditioning The triple-R

Al Stiefel included a sizeable pair of the Mapleshade amp stand for isolating the Red Rock Renaissance from the carpet in my fully-carpeted listening room. Each amplifier stood on four brass cones, and the Mapleshade stand further augmented the daunting height of the amplifier.

The Renaissance accepted RCA input only, so the 1.5-meter, 42-strand Audio Note Sogon™ litz silver interconnects ran the signals between each monoblock amplifier and the Wadia Reference Series 9 Decoding Computer, or the Pass Lab X0.2 preamplifier with the Audio Note DAC5 Special. Speaker cables were the Audio Note SPx 27-strand litz in banana termination. Power cables were the Furutech Power Reference III.

The 50-watt output of the Renaissance was not the most powerful among tube amplifiers, but its unprecedented level of sophistication in the power supply implementation set it apart from others, and the way the 95dB/8Ω Tannoy Churchill Wideband behaved when driven by the monoblocks revealed a level of performance I had not experienced from the speakers.

I have listened to a few medium-power SET monoblocks lately, and the Renaissance was the only non-SET able to meld with the Tannoy’s 15-inch Dual-Concentric™ driver in creating a spatial superstructure in the listening room of uncanny solidity, spectral coherency and dynamic scales. The effect was such, that the acoustic guitars in the Master Music XRCD24 Masterpiece, although possessing comparatively modest spectral properties than the likes of piano, reveled in the most extended spatial and spectral presentation I’ve heard. Even for a spectrally limited instrument as the acoustic guitar, the Renaissance-driven Tannoy seemingly anchored a much larger venue of wondrous spaciousness. The result was the most reverberating acoustic guitar sound, full of ultrafine variance in amplitude of the guitars.

It was an epiphany to realize that it would take such caliber of an amplifier combined with a large-diameter driver to deliver the most lifelike, surreal rendition of a handheld acoustic instrument. Perhaps it was the Renaissance’s ultra-flat spectral behavior that allowed the subtle dynamics and tonalities of instruments to emerge; but it was their recreation of the Lasting Impression Music’s K2HD disc Cantate Domino that showcased another facet of the Tannoy’s true prowess.

The presence of the soprano in Track 11, “Julsång” (Christmas song), spectacularly resonant in the most uncolored realization of her vocalization, was enveloped but not eclipsed by the dynamic colossus of the beautifully choreographed and soaring background chorus. The pipe organ that ushered in the music tranquilly from the beginning grew mesmerizingly in scale and volume as the Tannoy had never done so before; but it was the manner in which the full spectrum of the colossal instrument was meticulously laid down that created a penetrating effect.

I was enfolded in layers and layers of unceasing sonic radiation of clarity within crisp, colossal landscapes simmered with punctual dynamics, and full-scale volumes that were heightened by layers of spatiality. With the Renaissance brewing and the Tannoy radiating, the fiber in my body was energized and the hair on my head acquired static charge. Not a pretty picture.

To probe deeper into the RRR’s sonic disposition, I replaced the Tannoy with the MaxxHorn Immersion. Currently retailing at $20k, the current version of the Immersion has gone through three revisions, and the pair I have is of the 2nd revision, with improvement to cabinet bracing and bass augmentation in speed and output.

Numerous amplifications in both solid-state and tube varieties were rotated around the MaxxHorn preceding this audition and failed to impress me one way or another. If it was not a forwardness notably unmusical through the MaxxHorn when a solid-state amplifier was in place, then it was a severely truncated and sometimes, even a skewed spectral makeup from a tube amplifier equally imposing of its own character. It would certainly seem that aside from a heavily regulated, or even a redundant power supply scheme being crucial to create a tube amplifier of competence in passing on the original signal unscathed, application of components of compatible, complimentary characteristics would be of particular importance in attaining the most comprehensive reproduction of sound.

Thus, it was with the RRR that the Immersion, in a long time, was at once rid of the sterile interjection of blunt shadings, or the syrupy radiance compounded upon with artificially bloated spectral conveyance, and presented a most gratifying testimonial toward the caliber of the digital front-end, an experience difficult to come by.

Although Bob Spence of MaxxHorn told me that the revision implemented on the Immersion at my house was on the cabinet’s rigidity and bass refinement, I found the Immersion’s overall presentation further refined. In addition to the more realistic bottom-end, there was improved clarity in instrument rendition, so much so that clear textural distinction amidst a non-aggressive, natural-sounding timbral definition were consistently realized.

The Immersion’s PHL driver was no comparison to the Feastrex monster Alnico that Dagogoan Phillip Holmes reviewed recently, but the Immersion was at its most superlative as driven by the RRR, and the dynamics that the RRR accorded to the MaxxHorn as awe-inspiring.

In a replay of the Bruckner Symphony No. 7 with the late Herbert von Karajan conducting the Berlin Philharmonic, the MaxxHorn, for the first time in the most spectacular manner, fully conveyed the control and discipline that Karajan was so notorious of, one also marvelously and impeccably executed by the orchestra. Lesser amplifiers had always pushed up the scale of the ensemble but left behind the sparkle of the instruments without a trace, not so with the RRR: The sophisticated tonalities of instrument groups, together with the attendant harmonic richness and crispness of textures were all unveiled.

While it is mightily agreeable that the RRR are equipped with the most exhaustive efforts in power supply and regulations to provide the top level in amplification, it is utterly nonsensical to not use the audibly superlative in power cable design to feed such marvel of an engineering feat, so that the amplifier is at least not hampered in performance by inferior power cords.

Therefore, the ultimate performance of the RRR was realized by employing two of the Isoclean Super Focus power cords. Costing twice as much as the Furutech, the Isoclean drove the amplifiers to produce more pronounced bottom-end solidity and subjective loudness. However much was left of the remnants of a softer lower to upper midrange was categorically restructured by the Isoclean-powered RRR into a sparklingly crisp transparency, and I became acutely aware of the fine line between the ultimate in tube and solid-state implementations.

A punctual, agile and simultaneously sonorous orchestral presentation endowed the brasses with an ever-ascending aura accompanied by meticulously tracked bite. The extra energy provided by the Isoclean created more profound intensity, as if the brass section now possessed an urgency that was more heard than felt before. It was a wonder how much musical energy a 6-inch PHL driver could deliver; but when one factors in the preponderance of such amplification as the Renaissance, further advocated by the Isoclean power cables, then anything less would be preposterous.

Conclusion

The SET amplifier genre has always been known for its tonal glow in portrayal of instruments and not for the most uncolored rendition of sound. Yet, the Red Rock Renaissance monoblock amplifiers were the least colored-sounding vacuum tube amplifier I’ve experienced, SET or not.

Never had an amplifier that I have auditioned proven itself to be so indispensable by rendering itself utterly transparent in sound. With top electronics and loudspeakers, the Red Rock Renaissance became the ultimate conduit and interface with the loudspeaker.

For the Red Rock Reaissance was most indispensable and proved its own worth by presenting the most comprehensive suite of sonic prowess, while not producing any perceptible distortions. Without it, the audiophile with the goal of attaining sonic transparency via the vacuum tube amplification route would only have the one option that I am aware of: the $95k Audio note Ongaku. As the bridge between the source and the loudspeaker, the Red Rock Renaissance is the only choice next to the Audio Note.

Good, competently designed amplifiers have always shown me different aspects of my system, equipping me with new insights in my audio expedition. The Red Rock Audio Renaissance monoblocks, however, was one of those extremely rare equipment, such as the 47 Lab PiTracer CD transport and the Audio Note DAC5 Special, that impressed upon me the notion that the rest of my system was vastly inferior for accompanying them.

Output of tube amplifiers are determined by type of output tubes utilized, and with noted exceptions, only designs of exceeding physical proportions with significant tube counts can produce outputs equivalent to even their more modest-sized solid-state counterparts. With a quadruplet of the Svetlana 572-10, each of the Red Rock monoblocks was able to produce a 50-watt continuous output; but it was the powerful implementation in its power supply and regulation system that the Red Rock Renaissance sounded so definitive for its genre.

My personal preference in not disclosing whether I had purchased a reviewed product has been one of fairness to the companies. I don’t begin negotiations until the review draft is presented to the companies for fact-checking, which negates my ability anyway to state whether I have purchased it or not.

With that said, I found out that Lloyd Walker of Walker Audio purchased a pair of the Red Rock Renaissance during my auditioning. Let me close by enclosing Mr. Walker’s words on his feeling toward the amplifiers, as well as my gratitude to Mr. Walker for providing the following words:

Manufacturer’s Comments

“Dear Constantine,

Three years ago, Al Stiefel called me and told me about his amps. He asked if I would like to show with him at the RMAF. I said I might, but I would have to hear the amps first so he drove down with a set. The tube monoblocks I had at the time were well tweaked out. After listening to the Red Rock Renaissance amps, I liked what I heard and agreed to show with him and bought a set. I also treated the amps with our Extreme Super Silver Treatment. The amps were very good before and even better as they broke in with the E-SST. They are still in my reference system.

As you might imagine, we are very particular about the components we use to demonstrate our Proscenium turntable. The Red Rock Renaissance amps are a truly worthy product that we are proud to have in our reference system. And, you can’t find a better person to work with than Al. He is a fine individual who is dedicated to producing a great product. It is a pleasure to know Al and to have the Red Rock Renaissance amps in our system.

Regards,

Lloyd Walker”

Manufacturer’s Comment:

Constantine,

It is my pleasure to write the manufacturer’s comments as a follow-up to your wonderful review. We thank you for spending the time with our product and for the thoroughness of your review.

During the initial design process, we strived to design something special, not just another black box. We think we achieved our goal, but we realize that it is secondary to its function of amplifying the music signal to the speakers.

I was struck by one phrase you used which captures the essence of what the Renaissance is all about – “the Red Rock Renaissance became the ultimate conduit and interface with the loudspeaker.”

You used a couple of other phrases that I think capture the essence of a great audio product:

”I was enfolded in layers and layers of unceasing sonic radiation”

”… harmonic richness and crispness of textures were all unveiled”

Again, Constantine, we appreciate your efforts in describing our product to your readers.

New Marketing Approach

Red Rock Audio has decided to make the Renaissance easier to purchase and more affordable to audio enthusiasts.

We have decided to offer direct factory sales and have lowered the price accordingly.

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