Featuring 60 watts or more per channel of tube power, the amp’s ability to run in either triode or ultra-linear mode offers more versatility than most any other amp I know of. If you want to have fun with that romantic tube sound while keeping the accuracy option, then the ST-120 is for YOU!
Vacuum Tube Audio ST-120 Tube Power Amplifier
- Amazing soundstage
- Voicing can be varied between triode and ultra-linear mode
- Voicing can be varied by tube rolling
- Surprising bass
- Retro look (both a plus and a minus)
- Compatible with some original Dynaco parts
- Quality construction
- Available as a kit or as a finished product
The Vacuum Tube Audio (VTA) company is the brainchild of Mr. Bob Latino (power amplifiers) and Mr. Roy Mottram (preamplifiers). Doing business at the Tubes4HiFi.com website, all products are available Internet-direct. To get to the ST-120 directly, use www.tubes4hifi.com/bob.htm Based in Massachusetts (Mr. Latino) and in Puyallup, Washington (Mr. Mottram), the company sells to thousands of customers who strongly believe in American made products with TUBES.
No. of channels:
Single Pair of RCA (unbalanced) Jacks
R/L 5-way jacks set to (one of) 4, 8, or 16 ohm loads (extra jacks for more impedances available on request)
THD + Noise:
1.5% at clipping
20Hz-20KHz +/- 0.5dB
Recommended break-in time:
120 or 240 Volts
9.5″ W x 13″ H x 6″ D
$929 (kit form with 6550 output tubes) to $1,580 (pre-assembled with 6550 output tubes) Other options are available
1 year for parts / 90-days for tubes
Stereo Power Amplifier, Tube Amp, Integrated Amp, Made In Usa, Tubes4hifi, Power Amplifier Reviews 2016
- jRiver Music server 22 for Mac
- WAV files ripped from CDs
- Some SACD high resolution audio discs
- Oppo BDP-105 connected via DLNA and (sometimes) used as a DAC
- Apple Airport Express as a listening room WiFi source
- iPad mini running jRemote as a system controller
- Schiit Gungnir Multibit DAC
- Emotiva BASX PT-100 preamplifier
- Tekton Pendragon speakers
- BlueJeans Cable interconnects and speaker wires
- Emotiva power conditioner
- Room treatments by ATS acoustics
- Sound (above all)
- Parts Quality
- Ability to alter sound with different tube models or different brands of tubes
- Larger chassis option with IEC power cord
- Elimination of Dynaco slide switches & chassis layout
- Built-in bias-meter option
By the time tubes entered their golden era (mid-1950s to mid-1970s), most of the engineering problems of producing reliable and accurate amplifiers had been solved. Gone were the days of needing an electrical engineering degree to keep your equipment running.
Instead, companies such as Dynakit and Heathkit sold do-it-yourself kits that allowed you to build your own audio gear from a well-thought-out, carefully documented and easy-to-read checklist. Provided you could learn to solder and you could read, you could build your own stereo electronics that actually sounded good. OK, make that really good compared to most commercial gear available at the time. Needless to say, these companies were household names, and their reasonably-priced kits were wildly popular.
So what happened? The one-two punch of Japanese audio and trial lawyers. When companies like Pioneer, Kenwood, Sony, Technics-by-Panasonic, and others began producing and shipping in quantity, there was no longer any savings benefit to building your own gear. In addition to that, tube equipment that used 400 to 600 volts was just considered too dangerous for consumers to have access to.
And so the great names of the DIY era faded into history. Sic Transit Gloria Mundi.
Yet here at the birth of the twenty-first century, the VTA company rises from the ashes resurrecting the ghosts of Dynaco and Heathkit. It’s probably true that most of VTA’s sales are of pre-assembled amplifiers, but if it’s your predilection, you can order a kit and assemble it yourself! The disclaimers offered by the company make it clear that they’re not responsible if you fry yourself while assembling the kit (aka Darwinism in action), but if you follow the instructions, such a result is highly unlikely.
And before moving on, a quick philosophical comment about component cost. Throughout most of my life, my discretionary budget had to be split between a variety of family choices with the (small) remainder used for my audio hobby. For many of those years, a thousand-dollar-plus expenditure on audio gear seemed impossible. Yet in retrospect, the collection of purchases that I made and discarded could have added up (easily) to the cost of a single premium purchase that would have remained satisfying for many, many years.
So, to quote one of my parents – I was “penny-wise and pound-foolish.” And I’ll drop the conclusion to this review now – I wish I had encountered the ST-120 (or another component of its quality) many years ago. And without further ado – on to the review…
The chassis size and shape of the ST-120 is identical to that of the Dynaco Stereo-70 power amplifier. The advantage of this choice is that original Dynaco accessories (such as the tube cage) can still be purchased and will fit. The curse is that the clunky slide-switches and obsolete parts (the stereo/mono switch, for example) are ALSO preserved.
The original Dynaco chassis parts were made of nickel-plated steel, and few have survived the passing decades without significant surface rust. Although the ST-120 chassis has identical dimensions, it is made of heavier gauge metal (16ga VTA vs. 18ga Dynaco). Additionally, the VTA chassis uses non-magnetic stainless steel chassis plates and screws.
In addition to the upgraded chassis, the ST-120 also sports larger transformers than the original Dynaco amps, allowing for higher power output. These have tighter specifications than the original Dynaco transformers as well as wider bandwidth.
Regarding the original Dynaco ST-70, Mr. Latino says “The original driver board was made of an inexpensive phenolic material with open solder traces on the bottom of the board. This phenolic material was not very heat resistant and the board would many times turn black from heat under the 7199 tube sockets. The open solder traces sometimes lifted from the board. The carbon composition resistors found on the board would, after many years, stray from their original values.”
Regarding the ST-120, Mr. Latino says “The VTA board is made of epoxy/fiberglass and has no open solder traces. It has plated through holes so that parts may be placed on either the top or bottom of the board. It has an on-board power supply with Nichicon low ESR caps and an on-board bias system that allows individual biasing of each output tube. The new board also uses 1% metal film resistors that will not stray from their original value over the years.”
The chokes, power supply capacitors, input and output jacks and internal hookup wires are also upgraded beyond the original Dynaco specs.
Further, the ST-120 amp comes with switches allowing the output tubes to be run in either ultra-linear or triode mode (the latter with slightly less ultimate power output).
An optional stepped-volume attenuator can be added per the customer’s request that will allow control from the amplifier’s front panel. My unit was fitted with this part, although I left it at 100% and opted to control volume from a (remote-controlled) preamplifier.
Yet another option for the ST-120 is to use a solid-state rectifier rather than the usual tube-type. My unit was fitted with the latter. Should you opt for the solid state rectifier, then the VTA Time Delay Relay (TDR) is recommended to allow the tube heaters to warm the tubes before B+ voltage is applied. This extends their service life.
The amp can be wired with a single pair of speaker terminals set for four, eight, or 16ohm loads (your choice), or for $35 extra, any two of the impedance options can have separate jacks.
If you have children or curious pets in the house, and want to keep them away from the (very) hot tubes, original Dynaco tube cages can be had from www.dynakitparts.com. The cages cover the top of the amplifier, keeping hot gear away from curious hands & noses.
As to the design philosophy, Mr. Latino stated that the goal was to create a tube amplifier (in both wired and kit form) that would advance the circuitry and sound while correcting many of the things that the original Dynaco ST-70 amplifier received as cost-cutting measures.
That philosophy is both a strength and a weakness, in my opinion. Keeping to the original Dynaco chassis design allows backward compatibility with the Dynaco ST-70 so that owners of those amplifiers could upgrade their rusting chassis with the new stainless steel one. But it also keeps some of the “cost-cutting measures” including the cheap slide switches, the poor location of the power switch on the back of the chassis, and the captive (ungrounded) two-wire power cord instead of the currently-common IEC socket. Furthermore, the umbilical cord Dynaco sockets (on the FRONT of the chassis, that no longer serve any complete purpose) are retained. These are not only ugly, but are also the only way of checking tube bias.
I’d much rather have seen a more spacious chassis. This alone would have helped with heat dissipation. The abysmal slide switches could have been replaced with something more modern, and even a 12V trigger socket could have been added to allow for automatic on/off functions. The tube bias functions could have been clearly labeled, and the obsolete Dynaco connection socket dispensed with.
Nevertheless, the amp is what it is. And many (most?) like the design just as it is, thank you very much. So take my complaints with the grain of salt they deserve.
And finally, the tube complement – the three factory-supplied tubes on the driver board are 12AU7 Sylvania tubes. These tubes strike a balance between the more sterile and accurate Genelex Gold Lion tube sound and the more romantic sounding Mullard tube sound. One can also choose to use the (theoretically more linear) 12BH7 tubes, but I prefer the sound of the original 12AU7s.
Also, on the driver board, the two outermost tubes are merely phase splitters, with the actual amplification done by the center tube only. So to tube roll, the center tube alone can be changed to get 90%-plus of the differences in sound.
Right out of the box (I bought a wired amplifier – not a kit), the amplifier sounds very, very good; excellent dynamics and tight bass with no glare at all. This amplifier can be fitted with 6550, KT88, KT90, or KT120 output tubes (some use different bias). I’ve heard this amplifier with both the 6550 and the KT120 tubes. Of the two, the KT120s have more bass, but the 6550s have a better treble. The review listening was performed with the (factory-supplied) Tung Sol 6550 output tube set.
I found the triode mode more romantic-sounding than the ultra-linear mode. In fact, with a Genelex Gold Lion tube set, and the amp in ultra-linear, I’d bet that most wouldn’t be able to tell any difference between this amp and a good solid-state one. But the ability to change the voicing of the amp with the flip of a switch is a definite advantage.
Nothing much to this – plug in the tubes (they’re keyed only go in one way, so you can’t mess it up), set the output tube bias (a multimeter & small screwdriver will be required), hook up the speakers & inputs, turn it on – and instant music!
It should also be mentioned that tube amplifiers generally produce MUCH more heat than solid-state amplifiers. Therefore, ventilation is important. This amp should not be set directly on carpet, for example, because that will block the airflow through the chassis. So place the amplifier on a hard surface with plenty of vertical clearance above.
Additional equipment used for this review included:
First, some general comments. The amplifier is dead quiet. Even with my ears against the woofers and tweeters, I could hear no hiss, hum, or noise. My speakers are very sensitive Tekton Pendragons, so if noise of any kind was there, I’d be able to hear it. A quiet amplifier is indicative of good design – so the first impression was a reassuring one. With break-in, I expect the sound to improve. But even when new, the amplifier is impressive-sounding.
The treble on Feed the Fire by the Geri Allen Trio should be clean, crisp and extended. Cymbals, in particular, should be lifelike without any sibilance or splash. And as always, I contend that cymbals are one of the most difficult instruments for an audio system to get right. Price is never an indicator of success on the cymbal test. But the ST-120 is as good as I’ve heard.
The bells and other treble sounds in Icecream by Lou Bega should sound live. Background sounds should provide a sense of location. If the intro to this song doesn’t sound like a live sidewalk recording, something’s wrong! And yes, the ST-120 puts you there.
The opening brushed cymbal on Come Away With Me by Norah Jones should have sufficient brass and shimmer without excessive tizz. You’d think that this would be simple, but there are a lot of amplifiers that struggle to get this right. The ST120 does.
The treble effects in Mala in Cuba by Mala should jump out from the mix. Too smooth? Your amp isn’t doing the treble justice. Treble dynamics are preserved properly by the ST-120. Of course, this cut is included because I like electronic music. Not to your taste? No worries!
The unique tonality of Dolly Parton’s voice on Coat of Many Colors should be immediately recognizable and unique. Her somewhat nasal tone can easily become shrill with some amplifiers, but the ST-120 avoids that anomaly.
The voices of the Eagles’ Seven Bridges Road should be distinct, not just a blur. This is also a live recording, and the ambience of the crowd should show through. A sense of space should abound here, with the feeling of a wide-open outdoor stage – not an enclosed room. The midrange bloom of the ST-120 can be exceptional (maybe its best attribute) depending on the recording.
The voices of Free Hand by Gentle Giant should not only be present, but should also blend without blurring. Each voice has its own tonality, and the amp should keep them recognizably separate, as does the ST-120.
K.D. Lang’s voice on Sexuality should have just a hint of breathiness to emphasize the erotic lyrics. Hearing this song on the ST-120 was enough to stir up my single remaining hormone!
The string bass on Twisted by Joni Mitchell should be fat and (above all) should lack blur. Since bass blur is a traditional characteristic of tube amplifiers, it is a refreshing surprise that the ST-120 keeps the bass line crisp and tonally accurate.
The thundering bass of Dixie Chicken by Little Feat should be visceral and deep. The Grateful Dead is another band with plenty of bass thunder. The ST-120 brings it all!
Merill Bainbridge’s Mouth should have surprising and clear bass lines. This cut is a favorite of mine, and I’ve never heard it sound better than through the ST-120.
If Love Was a Train by Michelle Shocked should display bass dynamics as the electric bass guitar becomes louder and softer throughout the song. Again, the ST-120 keeps the bass crisp and tuneful despite the significant volume changes.
The dynamics of Milton Hallman’s piano performance of Capriccio in B Minor, Opus 2, No. 4 by Ernst von Dohnanyi should reveal the acoustics of the LSU Music theater. I have an advantage with this recording, since I’ve often listened to many live recitals in that very hall. With the ST-120, you get a feel for the size of the original recording space.
Imagining You by Leah Andreone should spread various sounds about the soundstage. This is yet another of my favorites. Leah’s breathy voice should be in the room with you – not spread over a 10-foot area. The ST-120 (despite its ability to throw an amazingly wide image on demand) keeps Leah’s voice focused and centered.
Erich Kunzel and the Rochester Pops orchestra plays The Syncopated Clock by Leroy Anderson just wonderfully. The auditorium size should be evident from the soundstage. The orchestra should sound very large, and I’d guess that the microphones used for the recording were close inside the curve of the players and on the stage. It certainly sounds that way, and the ST-120 brings the sound of an orchestra in an arc to the front of your room.
Diamonds on the Soles of Her Shoes by Paul Simon should also provide a sense of movement on stage during the performance. All of Mr. Simon’s releases seem exceptionally well-recorded, and I often use them to evaluate equipment. The ST-120 captures perfectly the chorus and the (separate and centered) voice of Mr. Simon.
The percussive sounds throughout Strauss’s Explosions Polka should be startling. The opening cannon shot, if you’re not careful, can damage your speakers (it IS, after all, a Telarc recording). As the echo of the explosions dies away, the decay should also be noticeable. With the ST-120, both the sharp percussive sound and the decay are clear.
Sleepwalk by Leo Kottke is a piece with a LARGE dynamic range. Many systems compress this or make it sound like a recording – not a real guitar in the room. The ST-120 again distinguishes itself by making this sound like Leo is in the room with you, but only if your other components are up to the task. One preamp I used, which shall remain nameless (not the Emotiva) made this sound like a recording, not like a real guitar in the room. But given a high-enough fidelity source, the verisimilitude of the performance shines through.
Linda Ronstadt’s Perfidia starts out softly, with just a strummed guitar and Linda’s voice. But when the orchestra comes in, the dynamic slam should grab your attention. Few amplifiers (tube or solid-state) get this right, but the ST-120 does. I’ve yet to determine why. With some amps the sound just gets louder, while with others, the transition to full orchestra is simply astounding. I’ve heard only one other amp that did this transition better than the ST-120. And, since I know that someone’s bound to ask “what was the other amp?” I’ll tell you up front that it was (surprisingly) a Luxman 1070 stereo receiver! Why that unit had the dynamics it did, I’ll never know – But I’m really sorry that I sold it!
Bye Bye Blackbird by Luther Kent should transport you to a New Orleans Bourbon Street jazz club. If it doesn’t, something’s wrong (but that something ISN’T the ST-120). Brash, sassy, and with some very loud sax and vocal work, this cut will give any amplifier a workout.
Since I have no electronic test equipment other than a multi-meter, I could not measure or verify the specifications. I will comment, however, that the distortion specification quoted by the manufacturer (1.5%) is the distortion at the clipping point (full power) and the amp runs at a much lower number throughout its functional range.
With the high-quality parts in the ST-120, I’d expect very good reliability. The VTA company has now been in business for 10-years and honors its warranties. Google the company for a feel of the current customers’ comments.
THE VTA ST-120 POWER AMPLIFIER is a Bargain in its Wired Form and an Unbelievable Bargain in its Kit Form. If You’re Looking for an American-made Tube Amplifier of Great Quality and Sound, You Will Not do Better.
What can I say? There are few other American-made tube amplifiers at the price of the VTA ST-120. The closest I can think of are the Audio by Van Alstine Ultravalve ($1,500 @ only 35wpc) and the Rogue Cronus Magnum (a fully-tubed integrated amp at twice the price of this unit). Of course, when you add the cost of a good preamplifier to the cost of the VTA ST-120, the Rogue may become more competitive.
You can get Chinese-made amplifiers for the price of this ST-120. But those tube power amps contain parts that don’t even approach the quality of those in the ST-120. In terms of ultimate value, I believe that the ST-120 is absolutely amazing.
What a nice amplifier! I plan to keep this one. Its 60-watts plus per channel (and that’s with the modest 6550 tubes!) is more than sufficient for my speakers, and the tube soundstage is to die for. Any equivalent amplifier from Audio Research, McIntosh or Conrad-Johnson would cost far, far more. Do yourself a favor – If you think you might be in the market for a tube power amp, put this one on your short list. You won’t regret it.