Category: Amplifiers
One of the genesis products of Spectral designed by Professor Keith Johnson. Lets begin with Keith Johnson description of the DMA-50.
Design Brief
This is the first amplifier to combine quickness, speed and brutality with meticulous design and performance detailing. Its miniturization is functional as its dense packed component arrangement assures fast in-phase response with precision timing along all circuit paths. Circuits feature quick responding bi-polar, J-fet, and large area enhancement mode amplifying devices, all cleverly arranged to make fast linear gain stages. Each channel has four of these, and each stage "is capable of very high drive current, overvoltage, and rapid charge sweep. Such high energy capability makes the following stage and load respond quickly without charge memory overhang from previous waveform events. Because of this, the DMA-50 responds in 0.0000001 second to overloads, cable reflections and other real system requirements. Moreover, this quickness is backed up by an 18 amp. 1,000 volt per microsecond output capability when needed. Hence with so much dynamic headroom, the DMA-50 will reproduce a DC to one megaHertz output signal virtually stress free.
This power, speed and quick recovery foundation sets the stage for very subtle and transparent reproduction. To do this, many design features from microwave technology and master recording electronics experience are applied. The most important ones eliminate subtle but cold, grainy, and often "skidderish" solid state sonics. Also, the amplifier is made unquestionably stable for all combinations of voltage, current, load, cables and wave time history conditions occurring anywhere in the circuitry. Unfortunately, in practice, all amplifying devices change characteristics with variations of these conditions. Vacuum tubes do this smoothly however, for the DMA-50, the well known abrupt solid state junction behavior is rounded and linearized with very carefully thought out and chosen interstage canponents. Gain stages then respond tube-like with an inherent low distortion, a more symmetrical voltage slew and near glitch free overload recovery. With less distortion coverup needed, feedback requirements then become less stringent thereby preventing internal overdrive problems that create the "kinks" and "funny stuff" all too prevalent with large complex designs.
Again miniturization pays off by allowing an almost inductance free grounding scheme and making frequency compensated dividers along the very small feedback paths. As a sideline, these very critical parts are oxide free exotic. metal construction yielding electrical accuracies only the most sophisticated test equiptment obtainable can measure. Such features improve sonics and assure absolute solid defined performance for any practical combination of loads and cables. Additional interference rejection occurs from a 50 mHz cascade front end gain stage giving isolation between the inner amplifier signals and the outside world of cables, preamplifiers and loads. Indeed, inner signals of many large complex high feedback amplifiers are extraordinarily distorted and harmonic rich. These tend to ripple through from stage to stage wi thin and often resurface at one or more connectors or grounds. Different cables and loads can alter these ripple through interference wave shapes thereby creating different sonics either at the amplifier or other equipment receiving this energy
The inherently linear and isolated construction of the DMA-50 eliminates these distorted currents and the resultant interconnect dependancy. Note that vacuum tube circuits inherently perform this isolation nicely. However, the cascade circuit is much faster and works well into radio and digital sampling harmonic frequencies. Those interferences near the audio range are well within the easy range of the amplifier and are passed through without consequence. Those above, which might cause subtle intermodulation noises, are common mode rejected by the fast input circuit. Hence, filters are eliminated. These and many other considerations result in unprecedented musical accuracy and unchanging stability, and as seen here, the DMA-50 performs flawlessly well beyond every conventional specification.
SPECTRAL DMA-50 POWER AMPLIFIER
Specifications
POWER OUTPUT :
@ 8 ohms = 80 WRMS @ 4 Ohms = 120 WRMS
BRIDGED 160 WRMS 220 WRMS
OUTPUT POWER P.K. @ 10% Duty Cycle
STEREO
@ 8 ohms = 140 Watts @ 4 ohms = 200 Watts
BRIDGED 450 Watts 260 Watts
OUPUT CURRENT: Limited to 18A Peak
DISTORTION: Less than .1% fran D.C. to 100 KHz 'IYPica11 y .006% @ 80 WRMS / 8 ohms
BANDWIDTH: D.C. to 1.2 MHz - 3db
RISE TIME: Less than 300 nanoseconds
SETTLING TIME: 500 nanoseconds
SLEW RATE: 1,000 volts/microsecond
INPUT IMPEDANCE: 10 K ohms
GAIN FACTOR: 25 db stereo, 32 db bridged
INPUT SENSITIVITY: 1.2 VRMS for 80 WRMS output into 8 ohms
SIGNAL TO NOISE: 90db unweighted
INPUT / OUTPUT ISOLATION: 80db
CROSSTALK: 70db
DIMENSIONS: 2.5 H x 19 W x 14 D inches
Keith Johnson
Music Used For Evaluation
LP Playback:
Bob James - Hands Down (Columbia FC 38067)
Hiroshima - Self Titled - (Arista MFSL1-525)
John Coltrane - Blue Train - (Blue Note BST 81577)
Wes Montgomery - Bumpin' - (Verve V6-8625)
Rickie Lee Jones - Self Titled - (Warner BSK 3296)
Wynton Marsalis - Live Blues Alley - (Columbia PC2-40675)
Eric Gale - Forecast - (KUDU Records KU 11)(CTI Records)
Kenny Burrell & Grover Washington Jr - (Blue Note BT 85106)
Earl Klugh - Finger Painting - (Blue Note MFSL 1-025)
Larry Carlton - Friends - (Warner 23834-1)
Sadao Watanabe - Autumn Blow - (Inner City IC 6064)
Doobie Brothers - Minute by Minute - (Warner BSK 3193)
Santana - Zebop - (Columbia FC37158)
Pat Metheny Group - American Garage - (ECM 1-1155)
Frederick Fennel - Cleveland Symphonic Winds - (Telarc 5038)
Paul Desmond/Jim Hall - Complete Recordings - Mosaic(MR6-120)
Time Out - Dave Brubeck Quartet (Columbia CS 8192)
Paul Desmond - Self Titled (Artist House AH - 2)
Ahmad Jamal - But Not For Me - Argo LPS 628
Bill Evans - At The Montreux Jazz Festival - Verve V6-8762
Bill Evans - At Montreux II - CTI 6004
Sunken Cathedral - American Gramophone - AG 361
No Bass Hit - Concord Jazz Label - CJ-97
Oscar Peterson - Night Train - Verve V-6 8538
Gerry Mulligan Reunion Chet Baket - Pacific Jazz ST 90061
CD Playback
Ben Webster At The Renaissance (Contemporary Records OJCCD-390-2)
The Royal Ballet Gala Performances (Classic Compact Discs CDSCD 6065)
Jurassic Park Motion Picture Soundtrack (MCAD 10859)
We Get Requests - The Oscar Peterson Trio (Verve 810047-2)
You Won't Forget Me - Shirley Horn (Verve 847482-2)
On Every Street - Dire Straits (Warner Brothers 26680-2)
Trio Jeepy - Branford Marsalis (Columbia CK44199)
Paris Jazz Concert - Louis Armstrong (RTE 1001-2)
Braveheart Motion Picture Soundtrack - London Symphony Orchestra (London LC0171)
Patriot Games Motion Picture Soundtrack (RCA 07863 66051-2)
Highlights From The Plugged Nickel - Miles Davis (Columbia CK 67377)
Private Investigations Best Of Dire Straits (HDCD) - Dire Straits (Warner Bros 49891-2)
Straight Up - Bob James Trio (Warner Bros 945956-2)
Land Of Giants - McCoy Tyner (Telarc 83576)
New York Reunion - McCoy Tyner (Chesky 5173324)
Gladiator Motion Picture Soundtrack(Decca 2894670942)
Copland - Appalachian Spring (Telarc CD 80078)
Frederick Fennell - Holst Suites (Telarc 80038)
Tchaikovsky - 1812 Overture (Telarc 80041)
John Williams - American Journey (Sony 89364)
Bizet - Carmen (Telarc 80048)
Live At Sweet Basil - McCoy Tyner Trio (Evidence ECD 22106-2)
Evaluation:
Most Class A output power amplifiers are huge behemoths weighing anywhere from 50 pounds up to 125 pounds or more, just seems to be the nature of the beast. I know over the years many Class A amps have come through here. Being 67 now I am not crazy about lifting and moving those amps. And most all high end manufacturers build these heavy Class A amps. Draw a ton of power from the wall and dissipate a great deal of heat.
So to see a Class A amp of this size and power is a revelation indeed. Over the years, and I remember when the DMA-50 came out in 1986 at a very lofty price. I did audition back in the day at a high end emporium and was totally impressed. However one has to remember that audition was in a controlled environment, along with a Spectral preamp. Very impressive audition, but I was still of a mindset that to reduce the size of a Class A amp could have long term reliability issues.
In the interim twenty four years, always had in the back of my mind to try for myself a DMA-50 or DMA-80. Recently this DMA-50 came my way, so figured it was about time to live with one for awhile. Plus the fact my neighbor had just scored a Spectral DMC-6 Preamp and a DMA 80 power amp. And spending some time listening to that system, brought back memories of my first audition experience with Spectral.
Now we have all heard stories about how one must use a Spectral preamp as well as MIT interconnects or serious sonic interaction could be possible. After reading the owners manual I could not find anywhere in that manual, where it was dictated that a Spectral preamp and MIT cables were mandated. So I decided to test the stories related to preamp interaction.
Not having on hand the requiste Spectral Preamp, the Threshold FET Nine was pressed into service, along with Discovery Cables from Joe DePhillips, along with Alon Black Orpheus speaker cables as well as a DH Labs power cord to round out the final amplifier connections.
Powered on the set up and waited some two hours or so for the warm up and let the electronics settle in. I can dispel the myth surrounding the use on non Spectral preamp and MIT cables with the DMA-50 no spurious interaction occured or has occurred with the use of the Threshold FET Nine. No pops or glitches of anykind have been present. So it appears to me that the use of non Spectral preamp and MIT Cables with the DMA-50 is a non issue.
Okay so what do we have here sonically. Have to freely admit upon first evaluation I was not impressed at all. Sure it sounded very good. But have had many very good amplifiers over the years and this was not on par with my neigbors Spectral system of same vintage. But nonetheless pressed on with the evaluation. Day seven of the evaluation is when everything dramatically changed. I had become accustomed to the sonics by now and was ready to change out the system. However this is the day when everything changed sonically. Finally the revelation I had been seeking with this setup. The depth, soundstage and transparecny came to life big time and damn near holographic experience. The richness of the music, the definition and above all the outright speed of the DMA-50 was a jolting sonic experience. My first experience with an ultra high bandwidth Class A amplifier was a somewhat startling experience, especially as jaded as I am now. Any experience in high end now I approach with a jaundiced view point. Perhaps way to long in this hobby.
While for me the jury is still out on this as a keeper. I am serously impressed. Do I spend the $475.00 to update and service the DMA 50? Just how much better will it sound is pure conjecture until it is serviced. I wish I could carp on something about the DMA 50, but thus far in its evaluation I find nothing to diminish its stature as one of high end audios legacy products of the past century.
Shortly I will pull a Klyne preamp from storage and see how that interfaces. As far as I am concerned no one produces a better preamp than Stan Klyne, not even Spectral in my opinion can out perform a Klyne. But more on that at a later time.
All I can say, that this, my first experience with a Spectral product has been very positive for this somewhat jaded audiophile of 53 years in this hobby/business. Perhaps I am waiting for the other shoe to drop.
Associated gear Click to view my Virtual SystemSimilar products Threshold, Pass Labs, Krell, Levinson, etc
