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Thursday, September 1, 2011

Dynamic Duo Review!
An Enlightened Warmth From
Rogue Audio’s Model 99 Preamp,
Stereo 90 Super Magnum Amp

Base Price: $2,595 (99); $2,595 (90)
Likes: luscious sound, bias adjust, USA build
Dislikes: internal speaker load adjust
More info: Rogue Audio

by John Gatski
From time to time, I like to do these Dynamic Duo reviews, where I pair two audio components that complement each other. The reviews can be from the same manufacturer, or sometimes from different companies. For this review, I picked the USA-designed and manufactured Rogue Audio Model 99 Magnum Tube preamp and Stereo 90 tube amplifier. Both have been on the market for a few years.
As a longtime audio enthusiast and reviewer, I have always held an appreciation for the designers who make tube-based gear. Nearly a hundred years after the first tube-based gear made its way into the electricity age, manufacturers continue to build, and customers continue to enjoy, the virtues of “valve”-based audio.
Rogue Audio’s Mark O'Brien and company have consistently introduced new tube audio products since the late 1990s. I like their approach of merging the essence of the tube sound — with modern internal components and signal flow designs — that complement the latest digital sources, as well as the stalwart analog sources.

The Magnum 99 Preamp
I have owned my Rogue Model 99 since 2001, and had it upgraded to “Magnum” status in 2005, which is now the standard configuration. It is my go-to tube preamp for review and personal audio listening. The 6SN7 tube used in the line stage exhibits a wonderfully smooth quality that, in the right design, also is quite accurate with fairly tight bass performance. Soundstage is wide and deep.
The Rogue Ninety-Nine ($2,595 base price) utilizes four hand-selected 6SN7 tubes, configured in a mu-follower circuit topology that enable that wonderful, smooth tube quality. Yet the high-quality capacitors, resistors and high-grade wiring enable the tube pre to match well with modern digital sources, such as high-end DACS and universal players. The external power supply — connected by a two retro-looking cloth-covered power umbilical cords, includes a toroidal transformer with high-speed HEXFRED diodes, seven separate regulators and a toroidal high voltage transformer.

The Rogue Ninety-Nine ($2,595 retail) utilizes four hand-selected 6SN7 tubes, configured in a mu-follower circuit topology that enables that wonderful, smooth tube quality.

My version contains the excellent-sounding phono preamp option (which adds $600 to the retail price), which utilizes four 12AU7 Russian tubes. The preamp also has a nice-sounding, headphone amplifier that taps into the line output stage, though the 1/4-inch connector is inconveniently located on the back panel.
The substantial Model 99 Magnum chassis sports a nice-looking, logically laid-out front panel with seven controls: an on/off switch, mute switch, multiple gain selector, volume, source selector, mono switch and record loop switch. The front panel is heavy duty billet aluminum and gives the preamp a classy, upscale appearance that belies its modest audiophile price.
The rear panel includes an array of input and output premium jacks for the four line components and the phono preamp. There are two twist-on connectors for the power supply cords. The preamp comes with a remote control, which is for volume only.

The Stereo 90
The Rogue Stereo 90 is a 90 wpc, KT-88/KT-90 based amplifier, designed in Class A/B push-pull topology. The tube complement also includes a 12AX7 phase inverter tube and 6SN7 signal tube per channel. The Stereo 90’s versatility is enhanced by its “mode selectability.” It can be operated in triode or ultra-linear mode via a rear panel switch. The Stereo 90 is a hefty amp, thanks to its heavy duty build, including the massive power supply and output transformers.
The Stereo 90‘s standard version retails for $2,595 and the Super Magnum version retails for $2,995. The Super Magnum version, which I tested, includes the following upgrades: KT-90 output tubes, HEXFRED bias supply diodes, screen-grid resistors upgrade, polypropylene bypass filter capacitors, bypass coupling cap upgrade, PRP audio path resistors, Cardas binding posts, Cardas RCA jacks, upgraded wiring, and upgraded signal tubes.

Four classic 6SN7 tubes
Removing the cover reveals the tidy, high-end assembly of the Stereo 90, and one of my favorite features, the manual adjustment of the tubes’ bias current. This feature allows the end-user to use unmatched tubes, yet still get optimum performance. The feature consists of a current meter, a switch that selects each tube and four mini-potentiometers (one for each tube) for adjusting the current. An included screw driver is used to turn the pots until the correct bias current is displayed via the meter for each tube.
While you are inside setting up the bias, you can also configure the speaker load for 4 or 8 ohm operation, via the internal speaker-tap wires. Dimension-wise, the Stereo 90 measures 18-inches wide, 15.75 inches front-to-back and 7 inches tall. It weighs in at 60 pounds.

The set up
I used the Stereo 90 and Model 99 preamplifier with a multitude of components and peripherals, including Alpha-Core solid-silver interconnects and speaker cables, Oppo BDP-83SE universal audio player, Esoteric DV-50 universal player, Benchmark Dac1 Pre D/A, Rotel RP-955 turntable, and TASCAM DVRA-1000 PCM-DSD recorder/player. Speakers included Legacy Focus 20/20s, Westlake LC8.1s and Legacy Studio HDs. AKG K701s were used for headphone listening via the 99’s headphone amp. Both the Model 99 preamp and the Stereo 90 were plugged into the AC using Essential Sound Products Essence cables and power strip.

The audition
In audiophile terms, $6,200 is a modest amount of money for made-in-USA audio gear, yet, there is nothing modest about the Rogue Audio tandem’s sound quality. The sonic signature of the two components relay a sense of tube warmth, smoothing digital’s sometimes rough edges in the midrange and treble, but showcasing the essential accuracy that solid state preamps and amps can deliver. The bass performance of the Stereo 90 in the ultra-linear mode is amazing; you could drive a subwoofer with this amp and not be disappointed.
On the Groove Note SACD Anthony Wilson TrioOur Gang, the warm-toned, hollow body jazz guitar, Hammond organ and drums recorded direct-to DSD was comfortingly analog in its presentation through the Rogues. That nice drum cymbal sheen and rich, organic Hammond organ overtones were there in force. Some tube systems sound overly bloomy on this recording — not the 99/90 combo; they projected the recording’s high-res warmth — without descending into the dark side.

The Super Magnum version, which I tested, includes the following upgrades: KT-90 output tubes, HEXFRED bias supply diodes, screen-grid resistors upgrade, polypropylene bypass filter capacitors, bypass coupling cap upgrade, PRP audio path resistors, Cardas binding posts, Cardas RCA jacks, upgraded wiring, and upgraded signal tubes.

In listening to Genre BertonciniBody and Soul (an Ambient Recordings SACD) masterful nylon string guitar recording of notable pop and jazz standards, the delivered sonics were even more impressive. The dynamic energy of the classical guitar was clearly evident with an expansive soundstage and nice transient energy to the string plucks. These tracks also revealed the Rogues’ excellent signal-to-noise performance and tube selection.
Speaking of tube selection, Rogue Audio’s Mark O’Brien told me that his technicians pay close attention in selecting tubes for the Model 99 preamp because 6SN7 tubes can get noisy as they gain hours of use. I have also noted this characteristic with the 6SN7. Even premium NOS USA tubes often get noisy. But the Chinese-based, hand-selected signal tubes picked by Rogue Audio stayed quiet and microphonic free for my testing. I have one set that dates back to 2005 — and not a hint of extra hiss or thermal noise.
On pop music, the 99/90 tandem was impressive on music that has good dynamic range. The Talking HeadsLittle Creatures 24/96 PCM Dual-Disc sounded great on this system, with a nice, open analog recording feel — with multiple layers of guitars, vocals and a little pedal steel guitar sprinkled in. The Elton JohnCaptain Fantastic and the Brown Dirt Cowboy SACD was a sonic showcase for the duo. Lots of detail from the analog tape-to-DSD transfer was clearly heard through the Rogues.
On really dense, modern power pop/rap/dance kinds of music (the kind mixed for the Ipod generation), the slight “warming” of the already hyped midbass and compressed dynamics of the music does not lend itself to the best sound with the Rogues; even some of the most expensive audio gear has trouble with such sonic “mud.” I usually avoid that kind of new music, though some of the earlier analog recorded and mixed rap music, (Public Enemy Fear of A Black Planet, for example), did sound pretty good via the Rogue siblings.

Handy bias adjust in the Stereo 90
I played a few LP records from my trusty Rotel RP-955/AT150ML cartridge setup to test the phono stage. The 99’s phono circuit is one of the best integrated designs that I have ever heard in a tube pre. In more than ten years of use, I would rank the phono stage’s lack of noise and dynamic quotient up there with much-costlier separates. Multiple plays of the latest remastered LP of Wes MontgomeryFull House and some old direct-to-discs LPs from Crystal Clear and other labels revealed the music, sweet music of well-mastered vinyl.
Ergonomically speaking, the Rogue tandem worked perfectly. All the controls and buttons were solid — without any noise. The tubes were hiss free and free of microphonics. Recommendations? Maybe putting the headphone jack on the front for the 99, and a speaker load switch on the 90‘s back panel, instead of having to change the wire jumpers from the inside.

The verdict
If you are shopping for an new amp/preamp, and want accuracy and that soothing quality of tubes, I recommend the Rogue Audio Model 99 preamp and the Stereo 90 amplifier as a matched set. Based on their performance and price, the pair receives our Everything Audio Stellar Sound Award — as a duo or as separates. You get great sound, relatively low cost, and plenty of functionality. Even as separates, you cannot go wrong when matching these components into a tube or solid state system.
And as a bonus, you get to support a USA audio company; Rogue Audio components are hand assembled in Brodheadsville, Pennsylvania.

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