January 2021

World Premiere Review!
Dynamic Sounds Associates Amp I
Class-A tour de force!
Review By Greg Weaver

  I've had the pleasure of writing about Dynamic Sounds Associates gear for over 16 years now, with my first take on the original Phono-ONE phonostage appearing back in November of 2004! Since that time, I've reviewed, or used as reference, the superb Phono II phonostage (with the Phono III coming on deck soon!), the exceptional Pre I Linestage (reviewed), and now, I am privileged to bring you the world premiere review of the exceptional Amp I monoblocks.

The engineering mind behind all these fresh and exceptional designs is one Dr. Douglas Hurlburt, whom I first met while living in southern Maryland during the early to mid-nineteen nineties. He was a member of my small, local, audiophile listening group.

The Soul Of A New Machine
Doug did his undergraduate work in mathematics and physics at the Johns Hopkins University, then obtained an M.Sc. in Solid State Physics, and his Ph.D. in Electrical Engineering, both from McGill University. His professional career began at RCA Ltd. doing development work in microwave integrated circuits and surface acoustic wave devices. He next moved to the MIT-Lincoln Laboratory where he continued to work on SAW device technologies and became involved in the analysis, design, and development of ultra-wideband spread spectrum communications systems and airborne radar systems. From 1988 to 1990, he served as a Program Manager at the Defense Advanced Research Projects Agency (DARPA), where he managed programs in hypersonic weapons technology and space-based radar. After leaving DARPA he stayed in the Washington, D.C. area and continued to provide consulting services, radar system analyses, and program management assistance for the Department of Defense (DoD) and other Government agencies until he chose to retire in 2003, whereupon DSA was officially born. 2012 saw him move from Potomac, MD, to a beautiful, gated community in Naples, Florida, whereupon he focused even more of his time and efforts on DSA!

The Amp I has been on Doug's virtual drawing board for some time, but when he finally was able to realize his unique output stage, the project began in earnest.

Matching the front panel aesthetic of both Pre I and Phono II, the Amp I is as gorgeous to look at as it is brilliant in design and execution. Mine arrived in their custom, foam-fitted, wooden crates, and were pretty straight-forward and relatively easy to uncrate and set up by myself. Standing an impressive nineteen inches tall on its specially modified "RiZE" footers from Critical Mass Systems, at seventeen inches wide and fourteen-and-one-half inches deep, and weighing in at eighty-two pounds each, the Amp I makes quite a physically impressive statement.

The fixed upper central section of the panel, a slightly thicker aluminum plate about four inches wide running top to bottom, roughly the upper one-third of the Amp I's height, has a centered Mode button that selects the operating mode, Standby or Run, has a mode select LED that indicates which operating mode is active, and includes four other status LEDs, one each for the amplifier section, the driver section, high voltage, and temperature.

Like both the Pre I and Phono II, there are switches behind a cleverly camouflaged, matching lower hinged central cover plate. This hidden panel on the Amp I also includes an LCD meter that, by use of a pair of multi-position toggle switches, allows you to check Output offset voltage, Output-stage operating voltages, or Output-stage bias current. There is also the Status LED dimmer switch, offering four varying brightness levels. Finally, an instruction card fitted into a recessed space, just for it, describes all options for their use.

Moving to the back reveals two massive handles running vertically along each side that are sturdy enough to allow positioning and can support the amp when lying on its back. Centered at the top is a small cooling fan, with a user-changeable filter, to cool the internal air volume, with selectable single-ended or balanced inputs side by side beneath. Below the inputs are two sets of five-way-binding posts (for easy biwiring), followed by the fan inlet port below them. Finally, near the bottom, to the left is an 18-gauge EIC socket, with a second 14-gauge IEC socket to the right. That's right, two power cords per channel!

The 18-gauge socket on the left has an integral AC power switch and fuse holder that is located between the power receptacle and the switch. This is the main power On-Off AC switch. Turning on this switch will provide power for the amplifier and driver sections of the Amp I, as well as providing 10 VDC for operation of the control functions and the LEDs on the front panel. The 14-gauge socket to the right provides AC power for the output-stage DC voltages.  If this cable is not connected, the Amp I will not provide any output power to the loudspeakers.

The large external heat sinks mounted on the side panels provide cooling for the output-stage positive and negative voltage regulators. The Amp I push-pull output-stage uses eight lateral power MOSFETs based on the legendary Hitachi high-power MOSFETs, now sourced from Exicon in the U.K. These devices are arranged in parallel combinations of four N-channel devices and four P-channel devices, each having a 0.1 Ohm source resistor to help linearize operation and compensate for slight differences in the gate-source voltages at the operational bias current levels.

Each of the eight TO-3 packages contains two "dies" that were adjacent pairs on the original fabrication wafer. The "double die" configuration doubles the total power handling capability of the individual packages and provides 1kW of power handling capability for each side of the output stage. These devices are mounted in a vertical fan- and chimney-cooled channel, one on each side of the Amp I's beautifully finished chassis. And, though the cooling fans may be audible when up close to the amplifiers, I never was aware of their sonic signature when playing music, even at the lowest of volumes.

The operating bias current is set to provide 125 Watts of Class A operation into an 8 Ohm load. However, the Amp I will extend smoothly into Class B operation under heavy load current conditions or when driving low impedance loads. With a frequency response given as 3Hz to 225kHz, while conservatively rated to output 125 Watts into 8 Ohms (in Class A), they can deliver over 300 Watts (in Class B) into a 4-Ohm load like my Von Schweikert Audio VR-55s or new ULTRA 9s.

The Amp I uses a unity gain driver-stage to isolate the amplifier stage from the high input capacitance presented by the multiple high power MOSFETs of the output stage. By utilizing four power MOSFETs in a dual Class A drive configuration, one pair for each of the output-stage inputs, it is fully capable of driving a very high capacitive load over a wide frequency range, and is largely responsible for the remarkably wide bandwidth of the Amp I.

Employing two custom-made shielded toroidal transformers and three power supplies, the transformers each have dual primary windings to permit 120VAC or 240VAC operation, and the individual power supplies are isolated from each other. The low-power transformer operates the amplifier and driver-stage and the high-power transformer is for the output-stage. Following the initial DC rectification and filtering, the amplifier, driver, and output-stages each have their own voltage regulators providing the highly stable positive and negative voltages required. The voltage regulators for the MOSFET power output stage are each followed by a 40,000 uF capacitor to provide reserve charge in support of heavy transient demands. To ensure a low impedance path for the high DC currents of a Class A amplifier, the Amp I power supply employs a 1/8" thick tin-plated solid copper metal ground plane that provides the "system" ground for the entire amplifier.

There is so much more to its remarkable and involved design, more than I can comfortably relate in this space, that I'd direct those who are interested in such details to go to the DSA Web Site, linked in the closing of this article. But now, let's get to the crux of this biscuit... how do they sound?

Making Music
During this review, I used the full DSA Monty, which includes my current reference DSA Phono II phonostage ($13,500), and the DSA Pre I linestage ($18,000), and, I may say, with exceptional results. The rest of my reference system includes the Kronos Sparta turntable powered by the Sparta Super Capacitor Power Supply, mounted with the Kronos Helena 10.5" carbon fiber tone arm, which in turn is fitted with the Etsuro Gold Moving Coil cartridge. As mentioned, my phonostage is the stellar Dynamic Sounds Associates Phono II.

Digital is rendered by either my own Windows 10 based PC, using J. River 27 (64-bit), Audirvana 3.5.40, or Roon 1.6, all optimized with Fidelizer v8.7, or my extensively modified McCormack UDP-1, both handing off to my Mola Mola Tabaqui DAC. The DSA Pre 1 linestage handed off to the Amp I monos, driving my ULTRA 9 loudspeakers. Everything rests on the Grand Prix Audio Monaco rack and amp stands, and Critical Mass Systems CenterStage² Footers. Power conditioning is managed by the superb Audience adepteRespons aR12, and a pair of Quantum Symphony Pro's, with the total system investment just eclipsing the $600,000 mark.

After installation and run in, their steadfast accuracy of tonality was the first attribute to garner my attention and admiration. Tonal colors were not only unquestionably life-like, they were regenerated with the refined subtleties and textures for which Class A amplification is so rightfully renowned. And, not just through the midrange, but broadband. Listening to my favorite classical recordings, from sweeping orchestral works and symphonies to chamber music, violin, or piano sonatas, I was treated to music infused with an unmistakably lifelike character, rendered with an astonishing measure of vibrancy.

Its remarkably honest voice is simply captivating, rich in musical resolve and harmonic texture, affording an exceptionally well-balanced mixture of both tonal truthfulness and emotional expressiveness. Instrumental voices were provided with all the body and bloom needed to complete that "live" illusion, recording permitting. Some might be tempted to call its overall harmonic envelope "tube-like," but that really isn't fair to the Amp I, as so many tubed entrants are euphonic or overemphasized in this regard. I just call it authentic!

Anyone who knows me, or is familiar with my writing over the decades, will know how much emphasis I place on the importance of accurate bass performance, especially down into the lowest levels and thresholds of audibility, as this region of the audio spectrum not only affects the foundation of the musical gestalt the machine can recreate, it has a sweeping and encompassing effect on the spatial recreation of the musical presentation as well.

The Amp I never faltered with even the lowest of frequencies, exhibiting both remarkable detail and speed, demonstrating an exceptional ability to render remarkably accurate and refined pitch definition. In many ways, its bass performance reminded me of my time with the WAVAC MD-805 Mk II monoblocks ($65,000/pair), which reconstructed some of the most engaging bass I'd heard to that point.

With rock masterpieces, like the cut "Hotel California," from the Eagles remarkable 1994 reunion tour, Hell Freezes Over [Geffen GEFD-24725], while the kick drum is located solidly deep into the stage and left of center, is created with enough impact to move your pant leg cuffs. Queuing up choice cuts like "Under the Boardwalk," from Ricki Lee Jones' 1983 Girl at her Volcano 10-inch EP [Warner 1-23805], or with the Poco Adagio from the sublimely powerful Symphony No. 3 by Camille Saint-Saëns [RCA LSC-2341], the bass is not only deeply yet accurately extended, with no bloat or overhang, it is presented with a palpable sense of weight and pressure that is uncannily like that experienced live. Granted, considerable credit for this illustrious accomplishment must be attributed to the abilities of my remarkable VSA ULTRA 9 loudspeakers, but I have heard amplifiers, some considerably more costly than the Amp I, that suffer an obvious roll off as they descend into the nether regions, giving up both pitch definition and slam.

And as such, spatial cues were recreated almost as well as I have ever experienced, with realistically sized instruments regenerated with a sense of bloom or body that was unmistakably correct, recording dependent, of course... as not all recordings can deliver to the same degree on these attributes. Listening to recordings like the Cisco Records release of Steely Dan's Aja [Cisco Music CLP-1006], the London Solti / CSO's Beethoven's Ninth [Mobile Fidelity Sound Lab MFSL 2-516], or even some QSound spectaculars like Sting's The Soul Cages [A&M Records 75021 6405 2] or Roger Waters magnum opus, Amused to Death [Netherlands CBS/Sony (2) 468761 0], and I quickly realized that the Amp I could wrangle staging and imaging queues just about as well as can be accomplished.

While some electronics will recreate instruments, especially piano or larger stings (double-bass or cello), with notable variations in size and/or with indiscriminate location as the pitch changes, the Amp I was unflappable in this regard. Regardless of the instrument being recreated, and independent of the frequency it was playing, instruments remained rock solid, unswerving in both size and location.

Treble is extended, airy, and nicely resolute, without ever getting grainy or etched in all my time with them. This extended and replete high-frequency performance bestows a sense of ease and relaxed enchantment to well-recorded materials and is a seductive and captivating characteristic.

One of the areas where the Amp I really shines is in its ability to render the space between and the sense of both the space occupied by, and the interrelationships of, instrumental positions and locations. Instruments and vocalists are portrayed with an uncannily realistic sense of size and locale. And while I freely admit that this is a hot-button for me personally, I nonetheless found this engaging and enchanting ability to be one of the Amp Is most impressive strengths over my time with these beautiful monoblocks.

While microdynamic shading is handled well, macrodynamic scaling is excellent, with little to no noticeable compression or limitation with large transitions, even at relatively loud playback levels. Crescendos in orchestral music, and fat bass guitar slaps or kick drum thumps are transmitted viscerally, with exceptional transient fidelity, un-slurred pitch definition, and physical impact in a way that nearly rivals the best I've heard.

Wrap It Up
To say that my time with this over-achieving Class A thoroughbred was merely enjoyable would be to deny its remarkable degree of rampant truthfulness and musical expressiveness.

This latest machine from the mind and workbench of Dr. Doug Hurlburt is not just another pretty face in the crowd. Dynamic Sounds Associates has hit another Grand-Slam Home Run with the release of this spectacular looking and performing amplifier. It is in a tough price class, with strong contention from the likes of the Classé Delta ($22,000 per pair), the Constellation Inspiration 1.0 ($28,000 per pair) and the Parasound Halo JC 1+ (17,000 per pair), both of which I reviewed for Positive Feedback, the MBL Corona C15 ($20,000 per pair), the Pass Labs XA160.8 ($27,300 per pair) that I reviewed for The Absolute Sound, or even the Zesto Audio Eros 300 monoblocks ($21,900 per pair).

There is no question that the DSA Amp I, when fed from its sibling Pre I and Phono II, provides a strong and symbiotic interrelationship. But have no doubts, it stands on its own four CMS footers without concern, or dependency on other DSA products. I also was able to feed it from my reference Audionet PRE G2 ($23,350), or even my ol' stand-by, the ModWright Instruments LS 100 ($3750), rolled out with an f32 Mullard GZ34 and a matched pair of 6SN7GT CBS / Hytron dual triodes. It has the sonic chops to allow those devices to show their true colors, to revel at the pleasure of the PRE G2, or reveal the subtle limitations of the LS 100.

For my money, what the DSA Amp I brings to the table in terms of its indisputable musical authenticity, with its richly colored, complexly harmonic tonality, its aplomb in the lowest octaves, its finesse and acuity at recreating the space of and spatial relationships among instruments – and retaining their individual dimensional veracity across the audio spectrum and at all volume levels, and its delicately detailed and extended high-frequency response, it would easily be my personal choice in its class. Most enthusiastically recommended!

Manufacturer Reply
DSA wants to thank Greg Weaver and Enjoy the Music.com for such a complimentary review of our DSA Amp I. In these extraordinarily unusual times, it's hard for smaller manufacturers such as DSA to not feel as if we exist inside a vacuum. Greg's carefully considered and beautifully written words feel like a welcome injection of oxygen into our existence. And most importantly, the music we are listening to is that much sweeter to hear. If readers have any questions that come up in response to the review, we'll be delighted to correspond. You can e-mail us at info@dynamicsounds-assoc.com. And let us say: "Enjoy the Music!"

-- Douglas Hurlburt
Founder & Principal Designer
Dynamic Sounds Associates

Specifications
Type: Solid-state Class A monoblock amplifier
Output: 125 Watts into 8 Ohms
Design: All JFET / MOSFET, push-pull 
Feedback: No loop feedback
Unbalanced Input: – 25dB
Balanced Input: 25dB or 31dB (User selectable
Dimensions: 17" x 11" x 18" (WxDxH)
Weight: 82 pounds
Price: $25,000 per pair

Company Information
Dynamic Sounds Associates
1754 Persimmon Ct.
Naples, FL 34109

Voice: 386-873-2388
E-mail: info@dynamicsounds-assoc.com
Website: DynamicSounds-Assoc.com