October 2023

World Premiere Review!
Rogue Audio Stereo 100 'Dark' Vacuum Tube Amplifier Review
Musical purity and natural ease bring out the very best in your loudspeakers.
Review By Ric Mancuso

Let's Hit The Track
Rogue Audio's designer Mark O'Brien has been on a tear lately with updated and new models that are setting the bar higher for the competition. I recently wrote about the new Rogue Audio Pharaoh II and the Sphinx Model 3 before the Stereo 100 Dark as reviewed here. You might say, they all came first under the checkered flag. Mark is a high-performance car and motorbike enthusiast, along with being driven — no pun intended — by his passion for premium audio high-end sound. I guess you could call him a gearhead. Hey, aren't we all at some level? Funny, how speedy motorbikes are a thing with other audio designers in the industry. To name a few, EveAnna Manley of Manley Audio, Sean Casey of Zu Audio, and Mark O'Brien of Rogue Audio. I have an exercise bike.

What does the term 'Dark' infer about the performance of the Rogue Audio Stereo 100 Dark? You would think it has to do with the amp producing a black noiseless quality that would increase the dynamic range capability of the amplifier. But no and yes! Mark tells me that the term Dark refers to the world of high-performance racing machines. When a car or motorbike is presented to a racing team before modifications, it is delivered in a prime black finish, along with requested tweaked competition parts. So, the 'Dark' connotation is of extremely high performance. We're not talking about a Vespa or a Fiat 500.

I love that we are reviewing a stereo / two-channel amplifier. The sound reproduction technology of stereo still hangs around after its invention many decades ago. It is not going the way of the Dodo bird. In addition, I'm not one for multi-channel audio, immersive audio, or home theater. I believe that a great stereo pair of speakers and amplification will deliver more than a complimentary sonic picture of a good film or soundtrack.

What's New With The Stereo 100 Dark Tube Amplifier?
The Stereo 100 amp has been out for a few years and has been updated with the following parts additions that comprise the composition of the Stereo 100 Dark:

Increased power supply storage
Hex Fred high-speed diodes in power supply
Polypropylene bypass capacitors in power supply
Nude Vishay and PRP resistors in critical locations
Rhodium binding posts (Cardas)
Rhodium RCA jacks (Cardas)
Upgraded signal wiring (Cardas)
Upgraded small signal tubes

Mark O'Brien says it's the sum of all the upgraded parts and tubes that make the big difference in sound quality. I asked him to identify the top three changes that make the Dark exceed the performance of the Stereo 100. He said, "It's more than just the three. The sum of all the little changes and fine-tuning of the parts is what makes the whole." The recipe is not unlike a chef tweaking the spices and ingredients of a delightful culinary dish. Upgrading parts in general will not automatically make a device sound better. It's how the implementation of the part changes the tuning and voicing of a sonic instrument. You can ask Bob Carver that question. Or if you could ask Bjorn Edvardsen of NAD or David Hafler that question?

Voicing was dependent on existing cables and speakers of the time to achieve the desired sounding result in a system. Carbon resistors and electrolytic capacitors were utilized in producing the NAD 3020 series 20 magnificent monster amp killer in the late 1970s. I've heard units with part modifications that sucked the life and magic out of the NAD 3020. I use a zip cord with the 3020 and it still sounds phenomenal!

Fine-tuning is the key to achieving a desired sound signature. Stradivarius is a fine example of a fine-tuned instrument. Many reviewers cite that a component or speaker from a manufacturer would have a "House Sound." I believe it's a little more than that. More likely, the designer aimed to render a sound that represents their tastes. From my experience, Rogue Audio integrated power amps and preamps do have that recognizable sonic characteristic that gives continuity to their product family.

Set-Up
The Rogue Audio Stereo 100 Dark vacuum tube amplifier is a solidly built unit. It will not escape the gravitational pull. The pitfalls of having a sound space in the subterranean location of the house require the reviewer to be in good physical shape to accommodate the task of landing a component down two levels of stairs. The amplifier out of the box is 60 pounds. The transformers are massive and heavy. Once jockeyed into position on the floor sitting on top of marble stones, the Stereo 100 Dark was ready to be dressed and outfitted with cables along with Black Ravioli Black Hole energy-draining pads installed on the bottom of the unit. Spikes have now become obsolete in my set-ups being replaced by the pads. More about those in a future review.

I used the supplied AC power cord. Speaker cabling danced between Analysis Plus and Cord Company sets. The amp then was left on for one hour, and then the power tube bias was performed. Oh, yes, first had to remove the amp cover to get into the guts of the amp. I left the cover off for the entire review process. Too difficult to put the cover back on once the amp is planted. It was cool to see the tubes glow anyway. Part of the magic show. Also, good access to re-bias when needed. Nice big meters made it easy to see the results. There is a handy biasing tool mounted to the chassis that makes the process easy to accomplish. The amp was left on for a long while to burn in and stabilize.

The binding posts on the Stereo 100 Dark are substantial and it was easy to secure the banana jacks as well as the Sigma Reference interconnects with the death grip RCA connectors from Monster Cable. Yes, they are still the ones to beat within my home audio sound system IMHO. Balanced connectors are also offered. There is a switch on the back of the amp to toggle between Triode and Ultra-Linear modes of operation. There are no feedback adjustments available. One blue LED light on the sparsely appointed face plate. Very much the same aesthetics as most other components offered by Rogue Audio. Simplicity and a non-distracting face plate. The power switch is located on the front panel. The medium-density foam packaging materials secured the unit snugly inside the heavy-duty box.

Beginning Listening Session
The first speakers I used to break in the amp were the entry-level Triangle BORA 2 bookshelf speakers. Highly efficient design that only retails for $500 a pair. I always hook up a pair of somewhat expendable speakers in case of an amplifier meltdown. Well, right then and there I was impressed with the sound of the pairing. It was so good in fact; I invited the owner of a prominent audio dealer in town to give it a listen. She was quite amazed at the instruments jumping out of the speakers!

Okay, so it was on to new territory with a significant speaker change. Next up were the Magnepan LRS ribbon speakers with a difficult 4 Ohm load to drive. The Stereo 100 Dark had no issues driving the LRS on the 4 Ohm taps. The bass was well-controlled and deep. It wasn't taut and snappy like a solid-state design like the Pharaoh II. The Pharaoh is a bass monster. However, the Dark was very satisfying and musical. Tube amplifier's Achilles heel has always been with bass response.

The Dark is one of the best tube amps I've heard producing bass. Upright bass instruments sounded tonally authentic on the LRS, even with their limited bass response. I did not feel the need to use a subwoofer with this combo. However, I do use a pair of the REL T Zero Mk III subwoofers successfully with the LRS and other stand-mount speakers to get more of a full-range presentation.

I employed the service of the preamplifier section of the Pharaoh to pair with the Stereo 100 Dark. I was experiencing what appeared to be noise coming from the Pharaoh. I removed the driver tubes and replaced them with another premium set with the same results, and again another set with the same issue. I was verklempt with this problem. I called Nick at Rogue Audio requesting an RP7 flagship preamp be sent out in the interim until I resolved the tube or whatever the problem was with the Pharaoh.

They sent out the RP7 and sent out a pair of long-plate JJ 12AU7s. The RP7 arrived. I installed the JJ 12AU7s in the Pharaoh, and the noise was gone! The moral of the story is, that different brands of tubes can react differently in a circuit. Rogue Audio makes sure the tubes they use will perform to their specifications and sound the best in their units. If you tube roll, be mindful of the possibility there may be some incompatibility issues electrically and sonically with doing so. Subsequently, I used the RP7 for the entire review. Lots of tubes in the RP7.Heavy device. The packaging was robust, you could almost ship a heavy amp in the box.

Continuing With The Magnepan LRS
Now with the system back together I got into the trenches with listening with the LRS. I played all types of music recordings from CD, Streaming, and Vinyl, including Classical, Jazz, Blues, and Rock. A mix of audiophile, and very good music, selections. I think a true test of a system is how well it delivers musicality with most types of recordings. There is an undiscovered treasure to be found in what you might think are below-average recordings. Overly analytical gear tends to only favor souped-up audiophile recordings IMO.

Being a radio announcer a couple of terms came to mind about speech quality. One is good diction and the other to avoid is an accent. Many components have a sonic accent, which calls to attention an identifiable unique accentuated sound. Maybe some artifact such as a bump in the presence region or tilted highs. Or a certain flavor of a tonal texture. These could be attractive qualities to some listeners. What I found with the Rogue Audio Stereo 100 Dark is it has good diction. Vocals are intelligible, natural, and not gritty or grainy. Some would say there is a sweetness in the HF range. Not overly tubey or syrupy sounding. Nothing is exaggerated or subtracted. Another term reviewers use is the term neutral. The neutral definition infers that "the tone was neutral, devoid of sentiment." This is not the case regarding the Dark amp. The Dark is impartial to any specific frequency anomalies and is truthful to tone, pitch, and dynamic expression.

The Magnepan LRS is a highly resolving speaker capable of fleshing out the strengths and weaknesses of amplifiers. It is one of my reference tools to assess the qualities of amplifiers. The Stereo 100 Dark was able to effortlessly power the LRS with ample dynamics and control. The soundstage was wide and deep with excellent transparency. There seemed to be no phase shifting and the stereo image was precisely defined between the speakers and extended beyond the LRS as the recordings would allow.

The robust power supply was no doubt responsible for anchoring the sound field authentically. Even with toggling between Ultra-Linear and Triode modes of operation. There was no exaggeration, added pizzazz, or sleight of hand with the Stereo 100 Dark. The music would command the performance with this pairing.

Listening To The Stereo 100 Dark With Falcon LS3/5A Monitors
The Falcon LS3/5A monitor speakers are a favorite near-field loudspeaker of mine. They tend to favor a good tube amp with magical qualities. Usually, those that employ EL 34 tube compliments. I had a pair of Manley EL 34 vacuum tube monoblocks that did the magic trick last year. How would the Stereo 100 Dark utilizing KT 120s perform with the Falcons? I connected the speakers to the 8 Ohm terminals. The LS3/5A speakers present a 15 Ohm loud to the amplifiers. I bounced between Triode and Ultra-linear settings. Let's have a quick refresher on the modes of operation:

Ultra-linear mode of operation, also known as, distributed load operation, is a term when applied to single-ended or push-pull vacuum tube audio amplifiers, that describes the output stage configuration whereby the screen grids (grid 2) of tetrodes, pentodes, or beam power tubes are fed from a tapping within the output stage.

In Triode mode, the speakers' impedance is directly coupled to the triode plate. This means that the triode gain goes up as the loudspeaker's impedance goes up. You get a little more output voltage gain to compensate for the loss of efficiency in the speakers.

Also, note that the power stage in triode mode has reduced power output compared to the ultra-linear mode.

Listening to the LS3/5A's is an immersive experience that can produce a sound field with a diorama landscape to behold. Now, of course, this all happens with the right tincture of lizard ears, the eye of Knute, and puppy dog tails. Yes, there is an abracadabra moment when it all is happening.

The Stereo 100 Dark did the potion justice. Tonal textures were rendered impressively. I preferred the triode mode, which gave me more spatial information. The triode mode is what I used for most of the listening session, which was lengthy. I like to live with a component over time to really understand the nuances and subtleties that govern its sonic character. I find if you get up in the morning and find yourself wanting to listen to music, then the component(s) have passed the test of being your musical companion. My house only has a limited inventory of beds and accommodations.

The British Falcons are superb at reproducing the human voice. The Stereo 100 Dark presented vocals beyond my expectations. I mean, real and goose-bumpy territory. Also, acoustic instruments were naturally unveiled and sounded truthful. The LS3/5A monitor loudspeakers were close to nine feet apart with vocals anchored dead center! And listening near-field along with the REL T Zero subs. Again, using the triode mode and discovering it to be more engaging and satisfying. I popped in the Sound Artist LS3/5A versions in the mix with pleasing results too.

More Speakers From The Audio Pantry
The Zu Omen Mk IIs, one of my favorite speakers, worked extremely well with the Rogue Audio Stereo 100 Dark. A high-efficiency speaker that made the most of the Darks capabilities and delivered life-like images with a top-to-bottom fluidity of sonic textures. There was no stridency or edginess with the playback. Purity would be the best term to describe what this amp is all about.

The ELAC Debut 5 loudspeakers were also in play. This was Andrew Jones's first designed speaker for ELAC. It brought down the press to its knees in 2015. I was there at the RMAF show when the Debut 5 was exhibited and demonstrated by Andrew. It continues to be one of my favorite designs. The Stereo 100 Dark did not miss the roll call with the Debut 5. The sound stage was gigantic and full-bodied. Beyond belief, like with the Triangle BORA 2. I mean, you could live with this pairing for a long time and not think about changing speakers! Luxurious premium high-end audio can be pricey, and at the same time packed with extreme value or a combination of both. I'm a cheapskate at heart and thus appreciate inexpensive audio gems that show their badges of incredibly great value.

Epilogue

Specifications
Type: Vacuum tube stereo amplifier
Output Power: 100 Watts per channel, two channels
Input Impedance: 200 kOhms
Frequency Response: 5Hz to 50kHz (+/-1dB)
THD: <0.1% typical, <1.0% at rated power
Input Sensitivity: 1.0V RMS
Dimensions: 18" x 17" x 7" (WxDxH)
Weight: 60 lbs.
Warranty: Three years, with six months on the vacuum tubes
Price: $4995

Company Information
Rogue Audio, Inc.
P.O. Box 1076
Brodheadsville, PA 18322

Voice: 570-992-9901
E-mail: info@rogueaudio.com  
Website: RogueAudio.com