Thiel CS2.4 and Harbeth Compact 7ES3.

Audio Research SP16 and VS55, Belles Soloist 3 and Soloist 5, McIntosh MA6600, and a Revox A722.

Musical Fidelity M1CDT Transport, Marantz CD5003, Squeezebox Touch with CIA VDC-SB external power supply, connected via Ethernet by Gen II Mac Mini running Snow Leopard, Western Digital and Seagate drive. Bryston BDA-1, Musical Fidelity V-DAC II, Revox A77, Kenwood KX-W8010 Cassette Deck.

Stager Silver Solids, Kimber KCTG and Silver Streak, Transparent MM2 Plus and Super, Element Cable Silver Serenade, DH Labs White Lightening, Transparent MM2 Plus (speaker), QED Genesis Silver Spiral, Acoustic Zen Tsunami II, Transparent PowerLink, Shunyata Venom, Pangea AC-9, DH Labs Encore, ELement Cable Red Storm, PS Audio (C7), DH Labs TosLink, AES/EBU, Coax, and BNC. Kimber OPT-1 TosLink.

Symposium Rollerblocks, Shakti Stone, Sound Anchors stands, Audience Adept Response aR6 power conditioner, Cable Pro Noisetrapper, Salamander rack.


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Positive Feedback ISSUE 70
november/december 2013


rogue audio

ST-100 Amplifier

as reviewed by Andre Marc


I have a decent history with Rogue products, having heard just about every model at audio shows and dealers. I have reviewed a variety of Rogue products including the Atlas Magnum and Hydra power amplifiers, and the Ninety-Ninety preamplifier, to name just a few. Rogue has enjoyed a loyal following for a number of years now for some very good reasons. They are part of a relatively small group of companies making tubed electronics in the United States. They also offer products at prices all audiophiles can afford.

I have often heard complaints that some of the old guard of tube component manufacturers based in the States priced many out of the market. Specifically, Audio Research, Manley, Conrad Johnson, VAC, and VTL seem to have moved on to producing products priced at the upper tier. There may be some truth to this, but these companies obviously see where their bread is buttered. Audio Research no longer makes an amplifier less than $5000.

The Rogue entry level Titan series, and their new series of hybrid tube and Class D designs, are well within reach of those hobbyists with modest budgets. They also offer more powerful, upper echelon gear for those who can afford more. The clincher is the entry level products show little, if any, compromise in build quality. Of course, realistically their top gear uses the highest grade parts.

Rogue also has a place in many sensible audiophiles' hearts because they don't product churn. They introduce new models when there is a breakthrough in design, or if they have found a way to substantially improve an existing product. I have heard from many Rogue owners that it is also nice to pick up the phone and speak to a person who may have helped design and build the very component they called about, right in Brodheadsville, PA.

As noted, Rogue introduces new products when there is very good reason to. Their line of hybrid Class D/tube designs made a big splash recently, with the Hyrda and Medusa power amps, and the Sphinx and Pharaoh integrated amplifiers. I know from speaking to Mark O'Brien, owner of Rogue Audio, that he felt the introduction of the KT120 tubes was a significant event, and most prior Rogue amps can currently work with KT120 tubes.

Rogue recently introduced the Stereo 100 (ST-100) power amplifier, the subject of this review. The ST-100 replaces the Stereo 90 in the lineup. The Stereo 100 is designed around four matched KT120 output tubes operating in push-pull configuration. A massive fully regulated power supply, a battleship chassis, both RCA and XLR inputs, and 4 and 8 Ohm speaker taps complete the picture.

Of note, owners can choose between "triode" and "ultra-linear" operation via a toggle switch on the back panel, more on that later. Parts quality is impressive. Rogue uses Mundorf EVO Oil coupling capacitors and custom wound output transformers, items not even found in some far more expensive products. Oh yes, the ST-100 is available for at an introductory price of $2995, and will eventually be priced $3495.

Here is a partial laundry list of features found in the ST-100:

- Heavy-duty gold plated RCA inputs

- Heavy-duty gold plated binding posts

- User selectable 4 and 8 ohm output taps

- User selectable triode or ultralinear output

- (4) KT120, (2) 12AU7, (2) 12AX7 tube complement

- Built in bias meter

- Integral tube cage

- Machined aluminum faceplate

- Mechanically isolated transformers

- Heavy (2 ounce) copper circuit board

- 3 year limited warranty (6 months on tubes)

Set Up & Listening

The ST-100 is a beast. It weighs 60 Lbs, and has a pretty decent sized footprint. Everything about it feels rugged. The Rogue Audio logo engraved on the bottom of the thick aluminum faceplate inspires confidence. The first order of business is removing the top cover, which entails removing a bunch of screws, then biasing the KT120 output tubes. The unscrewing takes longer than the biasing with the supplied tool. The accompanying manual specifies 40 milliamps.

I used the ST-100 with a Bryston BDA-1 DAC, a Channel Islands Audio PCL-1 MKII passive controller, with both Darwin Cables and Stager Silver Solids interconnects. I used both my Thiel CS2.4 floorstanders, and a pair of KEF LS50 monitors, with Transparent speaker cables. Both speakers were connected to the 4 Ohm tap. I used both the extraordinary Furutech PowerFlux and the excellent Acoustic Zen Tsunami II power cords.

The very first track I listened to with the ST-100 in the system was "Aquarius," the opening song from the movie soundtrack to Hair. It is a track I know well, and is a complex stew of syncopated rhythms, horn charts, a propulsive bass line, and Melba Moore's other worldly lead vocal. Within the first three minutes I was the guy in the Maxell commercial… hair blown back, totally immersed in the music and its power. The complex drum pattern, funky rhythm guitar, and backing vocals literally had me trying to process and come to terms with all the new layers of energy I heard in the recording.

The ST-100 was just broken in at a time when I was catching up with loads of CD and download purchases, and it was a fruitful time indeed. The ST-100 provided great rewards for smartly recorded albums like Stories Don't End, by Dawes, Jake Bugg's self title debut, Get Happy! by Pink Martini, The Diving Board by Elton John, Sting's The Last Ship, Jonathan Wilson's Fanfare, and Meet Me At The Edge Of The World by Over The Rhine. It also did not add any sugar coating to Pro Tools slop or rather flat sounding recordings like Paul McCartney's NEW. The McCartney album, by the way, is great musically, and the same goes for Patti Griffin's American Kid, great tunes, but brittle production. This showed me the ST-100 was a clean window into the music, and in no way emulates "classic" tube designs that lean towards the overly warm, syrupy side.

The ST-100 did, however, provide all of the classic benefits of tube amps. Namely, holographic imaging, sublime tonality, and a sense of liquidity and natural flow. It is also as quiet as any solid state amp that has come through this listening room, and bass control and articulation was superb. This was evident when I played the brand new Deluxe Edition of Van Morrison's uber classic, Moondance. I was completely taken aback at the clarity of the bass lines, the little touches in the mix that were previously homogenized in previous versions, and the sheer presence of the lead vocals and horn lines. This is a remaster/reissue done right, a rarity these days. The ST-100 showcased this masterpiece in all its glory, with real body and life like imaging.

During the review period the sad news came in that Lou Reed passed away, and in his honor I pulled the remastered CD of the David Bowie produced Transformer. This beyond iconic recording was a bittersweet listen, with the Rogue ST-100 extracting all the rock and roll grit buried in the mix. There was a distinct way the ST-100 allowed for a personal connection to all the albums I chose to listen to. It was especially true with Transformer, with its lurid tales and romantic overtones. Tracks like "Perfect Day" and "Satellite of Love" came alive through the ST-100. At this point I came to decide one of the ST-100 strengths was the sense of humanity it gave the music.

On the flip side, I was floored at the grace and delicacy the ST-100 exhibited when I streamed Miles Davis's sublime Seven Steps To Heaven, a seminal work from 1963. The opening track simply sounded stunning, with Victor Feldman's piano panned right, and Ron Carter's bass panned left, so very lifelike, anchored by Frank Butler's drums. Davis's trumpet floated gorgeously in space, with the correct amount of brassiness and presence one hears from a live trumpet, albeit without the sheer force of sound a trumpet makes. In my opinion, this can almost never be captured on a recording. Bassist Ron Carter recently described this album as coming at a time during one of Davis's most creative periods. Hearing it its entirety through the ST-100 was a real privilege.

Comparing the Audio Research VS55, retro-fitted with the same Tung Sol KT120 tubes that are supplied with the ST-100, was telling. At half the published power output, and with a design originally optimized for 6550 tubes, the ARC produced a smaller soundstage, and a more midrange heavy picture. The VS55 was clearly tubeier sounding, but a great sounding amp in any case. It simply could not match the ST-100 for bass articulation, stereo separation, and overall muscularity.

But to be fair, again, the ST-100 circuit was designed around the KT120, unlike the VS55, not to mention the discrepancy in power output.

Enter the LS50

After good amount of time with the ST-100 driving the Thiel CS2.4s, I received a pair of KEF LS50 speakers in for review. These mighty mini monitors have created quite a buzz. Designed to commemorate KEF's 50th anniversary, they feature a coaxial driver, and an enclosure made of advanced materials, and a price tag of $1500. I had heard some skeptical audiophiles claim the LS50s could not be driven satisfactorily with tubes due to their medium sensitivity and impedance plot. I decided to investigate. Apparently these folks had not heard the LS50s with the ST-100. The combination was simply astonishing. I found it rather surprising the size of the soundstage the ST-100/KEF combo created. Sitting near field, at 8 feet away from the speakers, I was engulfed in sound, with instruments extending so far from the plane of the speakers, it was a trip.

Speaking of tripping, Donovan's Sunshine Superman was simply transportative with the ST-100 and KEF combo. The title track and several other psychedelic classics like "Bert's Blues," "Ferris Wheel," and especially the cosmic "Season Of The Witch" had no business sounding as good they did, being 46 year old recordings. The ST-100 exhibited total control over the LS50s coaxial driver, which does require a bit of juice to get it moving.

UltraLinear & Triode

I did spend some time experimenting with the UltraLinear and Triode modes, which as noted are selectable on the fly via a back panel toggle switch. Overall I preferred UltraLinear about 75% of the time. They were ultimately very close, and which the listener prefers will be speaker, and possibly music dependent. Rogue says Triode offers the lowest level of distortion, but at the expense of ultimate output power. Ultralinear operation offers low distortion levels that approach those of triode operation, and for loudspeakers that demand high levels of power, Ultralinear should provide transparent sound and plenty of juice.

According to the manual, "The triode/ultralinear switch allows the user to operate the Stereo 100 in either of the two modes. In general, the sonic differences are subtle, but for a given loudspeaker one mode is likely to sound better than the other. There is a complex relationship between the output transformer and the crossover network, so try both and see which one works best in your system. This switch can be operated while the amplifier is playing but you will hear a small relay noise through the loudspeaker."

Special mention should be made of Darwin Cables, which Mark O'Brien recommended to me a while back. I used the Darwin Ascension extensively during the review. It is an all silver interconnect made in the USA, and available directly from the Darwin Cable website (www.darwincables). It is a terrific sounding IC that was a great match for the ST-100.


My time with the ST-100 was one of the most musically enjoyable in recent memory. At an introductory price of $2995, it earns my highest recommendation in regards to sonics and value. It is virtually maintenance free, aside from periodical tube biasing. As with all the other Rogue products I have had in house, it was 100% reliable.

The Rogue ST-100 is almost too good to be true. 100 watts of tube power, superb sound, built like a tank, and it does not cost a fortune? Count me in. So what does the ST-100 give up? Maybe, just maybe those last few percentage points of refinement that the very best tube amps in the world offer. This is up to sophisticated listeners to decide for themselves. Personally, I would live with the ST-100 happily ever after, without hesitation. Andre Marc

ST-100 Amplifier
Retail: $2995

Rogue Audio

A an interview with Mark O'Brien of Rogue Audio:

1) Andre Marc: What did you think when you first encountered the KT120 tube and where does it stand among other well known output tubes?

Mark O'Brien: When the KT120s became available I listened to them at home in my reference system and was really "wowed" by their sound. I don't generally hear as much of a difference in output tubes as I do the small signal tubes in an amp, but the bass and richness of these tubes was immediately apparent. Before we started using the KT120 in production we sold a few hundred quads to friendly customers looking for their feedback. The response was overwhelmingly positive and they seemed to be extraordinarily robust. We used them in limited products for awhile and now use them almost exclusively.

2) Andre Marc: Can you tell PFO readers about your current product lineup? It seems there are some exciting things going on.

Mark O'Brient: The new Sphinx and Pharaoh hybrid integrated amps are really exciting from a price to performance standpoint. The fact that they run very cool, and require no tube maintenance, is also very attractive to some of our customers.

That said, we are primarily a tube company and our latest product (which you have just reviewed) is just the beginning of some really exciting new products we will launch within the next year. We are presently working on some new preamp designs that will have features not previously seen on our gear. More extensive remote functions as well as display technology will be a big part of our next generation equipment

Review Reference System

Preamp: Channel Islands Audio PLC-1 MKII, Audio Research SP16L

Power Amp: Bob Carver VTA20s, Audio Research VS 55,

DAC: Bryston BDA-1, John Kenny Ciunas USB DAC

Transport: Musical Fidelity M1 CDT

Streamer: HP Laptop running Windows 7 & Jriver 19, Squeezebox Touch

Cables: Darwin Cables, Stager Sound, Transparent, Furutech Flux Series, DH Labs (Digital),

Accessories: Audience adeptResponse, Symposium Acoustics Rollerblock Jrs

Speakers: Thiel CS2.4, KEF LS50