Review: Spectral DMA-50 Amplifier

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.




@ 8 ohms = 80 WRMS @ 4 Ohms = 120 WRMS


OUTPUT POWER P.K. @ 10% Duty Cycle


@ 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


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



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)


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 System

Similar products
Threshold, Pass Labs, Krell, Levinson, etc
I have two Spectral DMA-50s that once drove two fine Nestorovic speakers for years and fried quite a few expensive Panasonic ribbon tweeters along the way. As a novice, I thought that this was what hi-fidelity was supposed to sound like, but I always felt like something was missing. Maybe it was me. I did not have the golden ears necessary to appreciate a pair of fine esoteric and very expensive Class A amplifiers. Then one day, for a goof, I switched out the two amps, running in bridged mode, with a cheap $199 Alesis professional amp purchased on eBay. I was amazed at what I had been missing: high end sparkle, spaciousness, and punch in the bass. Recently, I switched over to two NAD 2400 amps, which sound even better. When it comes to Spectral, I am saying the emperor has no clothes.

I was fortunate enough to speak with Mr. Nestorovic on the phone before his untimely passing. The man was an audio genious who designed some of the best audio equipment in our time. He advised me not to use Spectral amps with his speakers because they amplify signals outside of the audible range and can clip violently and destroy speaker drivers. After my fourth tweeter replacement, I have learned my lesson and have placed the Spectrals on moth balls. I do not recommend Spectral amplifiers.
Your points ae well taken. Spectral is not for everybody in the realm of high end audio. To achieve the best from these products Spectral components should always be used with other Spectral products. In for instance a Spectral amp and preamp with the associated MIT interconnect cables made for Spectral components. I have no doubt on your experience with the Spectral amplifiers, it has happen before and most likely will happen again. But with the given of using Spectral as recommended by the manufacturer and speakers that match well with Spectral, there is in my opinion little to carp on. I still remain very impressed with Spectral. Is it the holy grail of high end ? In a word NO. The best I have ever heard has been FM Acoustics, but at their price points only a few will ever own. However Spectral products remain as one of high end truly enduring products, that have kept the promise of high end, when of course used in conjunction with other Spectral products.
I find both responses accurate: Claydawg's description of the sound with *most* Spectral products up until 2-3 years ago or so; and Ferrari's technical description on how to avoid ruining speakers.

More to Claydawg's points, the sound of their older products was very hi-fi and/or dark for me too - and I have been using their products for over 15 years - until I upgraded to the latest generation. Today's Spectrals have nothing to do with the old ones, and I find them extra-ordinarily realistic. There has been a staggering change in their sound, say, between the DMC-20 and the latest DMC-30, or the SDR-2000 and the latest SDR-4000; ditto for the amps.

For all intents and purposes, the DMA-50 is just too old to represent their current thinking or state of the art.

There are some nice discussions on the Spectral forum on
I have owned spectral amps DMA 50, 80, and 90; pres 6, 10, and 12. I was not as impressed with the pres as the amps. Personally I do not like MIT cables. I liked PAD Collossus much more. but I liked Gabriel, Jade and I liked my own (gold plated silver) most; way back when. King Cobra power snake was great behind them. I didn't like the 80 as much as the 90 or 50 (last for tone). In the 50, I upgraded the posts, RCAs input and output wire.That was a long time ago, and I know I could do better today. That amp runs a small housesystem with huge towers to this day. I'm currently looking for a DMA 200. Beautiful gear. And I'm really glad to hear there was nothing in the manual about matching gear and cables. I also wouldn't mind a Krell KSA 50. ; )