December 27, 2019 9 min read
Readers of Positive Feedback may already be familiar with Justin Weber's creations. At least two reviews of his products can be found in these pages. Known for elegant and physically small pieces that punch way above their weight class, this amplifier is no different, and this is actually the second review of this particular unit, having appeared in 2016 in a review done by Steve Lefkowicz (HERE).
I feel this is an appropriate place to inject ampsandsound's mission statement:
"Welcome to ampsandsound where it is our mission to create engaging audio components that offer superior sound quality at prices that music lovers can afford. Our focus is on amplifiers and loudspeakers. Our products utilize proven theories, solid engineering, and quality manufacturing here in the United States. Our goal is to make better sound quality accessible.
"Part selection matters deeply to us; we source only the highest quality parts and design our products to offer genuine value, reliability, and the best possible sound quality. At ampsandsound, we strive to procure most of our world-class components from domestic suppliers, including our signature top plates, chassis, transformers, and PCBs.
"Because we seek to build something worth passing down, we personally hand-assemble each one; making every amp and speaker a statement of our commitment to quality at a very reasonable price. Our design aesthetic is functional and sophisticated, right down to the hand-finished solid wood cabinetry.
"We designed our amplifiers for daily performance and longevity; if need be, they could be easily serviced 15 to 20 years from now. We employ three significant components; capacitors, resistors, and diodes. No silicone voltage regulators or integrated circuits to hot-rod our designs. We stand as a classic example of American craftsmanship and value. Our amplifiers are beautiful and simple, with a non-fatiguing sound that has been enjoyed by previous generations and will be equally enjoyed by those to come.
"Music is meant to be a transformative experience, and our handmade audio components allow you to do just that."
So why are we back with this little champ? Well it seems that Justin imparted some serious upgrades to the units post the review from Mr. Lefkowicz, creating an amplifier with a lower noise floor and greater bandwidth.
The specifications of this little giants is as follows:
2 EL84 tubes in push-pull configuration with ½ of a 12AX7 and ½ of a 12BH7 per channel and a GZ4 rectifier tube.
Power output is now up from 15 watts per channel to 17 watts RMS with peaks of 22 watts @ 1kHz.
Input impedance is 500Kohm, 1.6v for full power.
With inputs shorted output noise is 5mV P-P.
Maximum Power @ 1kHz = 22 watts RMS.
246mV P-P = 1 W RMS 10Hz (-0dB) – 27.4 kHz (-1db).
550mV P-P = 5 W RMS 18Hz (-1dB) – 22 kHz (-1db).
796mV P-P = 10 W RMS 26Hz (-0dB) – 15.5 kHz (-1db) (Before Distortion) .
10 Hz – 30kHz (-1dB) @ 1 watt.
18 Hz – 20kHz (-1dB) @ 5 watts.
26 Hz – 17Hz (-1dB) @ 10 watts.
4 and 8ohm speaker taps (8 and 16ohm taps are an option).
Where the Stereo 15 Special Edition differs is in the use of custom wound transformers made exclusively for ampsandsound. The power transformer is nearly twice as heavy as the unit used in the Stereo 15, and allows for greater current delivery/reserves and the use of a tube rectifier. Justin has specified the use of a GZ34, and can accommodate GZ37s; 5U4s allows NOS rectifiers.
The unit arrived in a bright orange Pelican style transport case with a handy pull up handle and a set of wheels. Made it so easy to get in the house and certainly protected the unit. Inside were the amp, all tubes, and the user instructions.
While I was unboxing it all I reached in for the diminutive amp (approximately 16" x 9"), I was stunned at how much it weighed. Clearly the transformers are heavy duty items. Setup is straightforward and easy. The amp is built on a single plate topography. Inputs and speaker taps run on the top along the back of the amp along with the input for the power cord. This amplifier can fit on a standard rack with a lot of room around it to breathe, which is how it was located in my system.
As a caveat to my time with the amplifier, I had two sets of speakers. One with an 87dB sensitivity and the other with a 91dB. These are not the friendliest, nor the first choice of speakers to pair with a lower power tube amp. That being said, I soldiered on curious as to how the amp would represent itself with those speakers.
My VonSchweikert VR4 speakers had the more friendly sensitivity of 91dB at 4 ohms, so I started there. I ran background music for a couple of days while doing my chores etc., giving the ST15 time to run in. I do this same routine with just about everything. Let it settle into the rest of the system for a couple of days is never a bad thing. Even from the beginning, before doing any critical listening, two things I was absolutely sure of was that this little guy has some big chops. I also know that careful selection of speakers with mid 90 and up sensitivity ratings are where this amplifier would be at its absolute best overall. (More about that later)
Driving the VSR4 to reasonable sound levels was not a problem, just required a little more gas through the volume knob on the preamp. This never produced the earth shaking delivery of something with ten times the power, but gave an outstanding accounting for itself in terms of sheer musicality, soundstage, air, depth, and breadth of the image, and a pinpoint fine center focus.
I found that overall the highs and mids that the ST15 SE produced were as good as I have heard from any amp. As I said, musicality is this amp's forte above all else, in my opinion.
There is no doubt that this amplifier would come into its own with a speaker having a sensitivity of 97+. I really wished, as I listened to it, that I owned a set of Avantgarde speakers. (Something I have long desired after hearing them numerous times sounding absolutely stellar driven by as little as three watts.) Having said that, they did a good job with the VR4s.
Listening to the track "If Ever I Would Leave You" by Jacky Terrasson, featuring Cassandra Wilson on vocals from the Rendezvous album (Blue note), the album is a collaboration between Terrasson on piano and either Lonnie Plaxico or Kenny Davis on bass and Mino Cinelu on percussion. It is a austere track that focuses on highlighting Cassandra's smoky vocals above all else. Jacky and the ensemble underscore her with a very lilting piano track, prominent upright bass, and sharp and sizzling percussion. What I found with the ST15 SE was that Cassandra's vocals were delivered with a sense of depth and breadth, and an intimacy that placed her directly in front of me as though I was sitting in a club, one table away from a slightly raised stage. Her vocals were so alive, and the tremendous control she exercised in her performance was palpable. The rise and fall of her voice was accompanied by the requisite detail of breathiness and sibilants that as I closed my eyes in the dark, I could sense her moving in and out from the microphone to regulate the volume. That is some serious detail, and it was all so creamy smooth in the delivery that it truly took on the nature of a live performance, not a recording. This one track made me sit up and take such notice that I played it three times in a row to make sure I wasn't interjecting something into the experience that was just imagined. After the third time I realized that this little 17 watt champ had some true magic to it.
For a bit more punch in the music I moved to Diana Krall and a track that I had almost forgotten over the past few years. From her Wallflower album (Verve) the song "California Dreamin'" provided more in the way of softer, smoky vocals that Diana is known for laid over a busier arrangement of her foursome and strings arranged by William Roos and David Foster. The ST15 SE did a great job of rendering her vocals true to that nature. I have everything she has every recorded, have seen her in concert, and the delivery was spot on. At times her her voice almost has a whisper quality to it, especially when she trails off. The ST15 SE provided that all the way to the fade out. It also provided a very good delivery of the instruments, including the breadth the and depth of the soundstage that as it swept across the room. The bass was deep and satisfying enough to not be a distraction, and the strings were so vivid and smooth. The percussion was sharp without any bloat.
On quartet type jazz, like The Eddie Hogan's trio with Scotty Hamilton on sax, the delivery was stunning. Lately I have spent a lot of my musical focus traveling back in time to when I was a kid in the fifties (good lord did I just admit to being that old), and to the music of my parents who were jazz fanatics. The album My Foolish Heart (Venus), the title track is just a great example of a very cohesive set of musicians that weave around each other with a sense of being mentally tied together in perfect synchronicity. Eddie's deft piano, with Jay Leonhart's exquisite bass, and Joe Ascione's sublime drums, laid the perfect base for Scotty Hamilton's breathy sax. The room just came alive with the musicians, and I could feel the air pulse from Scotty's sax. The cymbals had just the right amount of sizzle decay, and the bass was never bloated. Crisp but not grainy. Sharp and precise without being analytical and cold. That is a lot to get from 17 watts pushing a 91 dB speaker. It was here that I realized what could be possible in terms of ultimate dynamics with a high sensitivity speaker, and the Avantgarde speakers kept coming to mind.
I decided to play some rather serious rock and roll, and turned to Jethro Tull's "Aqualung" from the album of the same name (Mobile Fidelity Sound Lab OMR MFSL 1-061). What a change in direction. Again the little ST15SE stepped up to the plate and delivered everything I could expect from it. Ian Anderson's flute playing is rather unique as he spins between straightforward classical flute playing while also chuffing out the notes and speaking at the same time. The performance was just as expected with all the breathiness that comes with his playing, Martin Barre's guitar rocked through the song, his touch is notable and his rhythm just blasts through the song, showing off what an accomplished note master he is. The distortion of the guitar was rendered with just the right amount of bite without sounding too fuzzy, which sometimes can happen with certain amp/speaker combos. Not in this setup. Just perfect. The thunder of Clive Bunker's drums was a bit restrained, but not enough to keep me from enjoying the track. The rest of the music was there in full measure and glorious.
Justin made the claim that the amp was absolutely quiet, and I will say that it was just that, and I found that amazingly true to his statement. I had my ear right up to the driver and the amp turned up, and there was absolutely nothing. I have not ever experienced that, but then again I never had a manufacturer make that claim, so I never tried it. Now I am doing it with every amp that I have. Some of my more expensive gear actually will produce a very slight hum when jacked up to full throttle and no signal. I did attribute it at one time to a noisy phono stage that I brought out of the archives for a quick substitution, as one of my faves went back to the manufacturer for an upgrade. Other than that, I had never done the challenge. Now every amp I audition and review will be subject to that Justin Weber test.
I found that design, using low output tubes, sharing of tubes for both channels, to be an interesting design, but it provided hours of seriously enjoyable listening. If I get my hands on some horns I may ask Justin to let me do a follow up, just to see how much dynamics it could produce driven hard through a set of 100dB sensitive speakers. Judging it from what it produced through the VSR4s, I am thinking it may be close to a euphoric little amp.
I did run it through the 87dB monitors and found it much less satisfying, but one cannot expect to mate 17-watts with 87dB monitor and expect earth shattering presentation so I went back to the VSR4s for the duration.
The fit and finish are top notch, even if the cabinet and overall look is a bit retro. I love retro. I got some serious compliments on both the overall look and the size. Not everyone wants ginormous amplifiers and thundering towers of speakers, and I suspect those audiophiles would do well to check out the entire line of ampsandsound products. As for the Stereo ST15 Special Edition, I can wholeheartedly recommend it if you are careful about speaker pairing and using a high efficiency speaker to get the most out of this amplifier, I doubt you would be sorry. You might even think about pairing it with a self powered speaker that powers the lower end, but can still be run on the top end by the ST15 SE. VonSchweikert Active speakers come to mind. Ether way, this is a amplifier that defies its relatively inexpensive price tag, and delivers way above that price with the right speaker pairing. I may well consider this or a set of the monos when I eventually downsize my system and go with a set of Avantgarde Unos! Now that would be a heavenly pairing... .
Stereo ST15 Special Edition Amplifier
April 28, 2021 1 min readRead More