The DMA-90 High Resolution Amplifier

The DMA-90 is an unmistakably Spectral product in the iconoclasm of its approach and the elegance of its solution. Spectral amplifiers combine the oft-praised "musicality" and naturalness of the best tube designs with solid state's low level detail, powerful output capabilities and long term stability. The DMA-90's extraordinary accuracy in the measurable dimensions is matched by sonics of incomparable clarity, transparency and musical coherence.
Every new Spectral product marks a chapter in Spectral's ongoing quest to identify and eliminate subtle musical distortions and noise. The DMA-90's speed and wide stable bandwidth are signature traits of a Spectral amplifier. So also is circuitry incorporating design features and high technology components which reflect the most advanced practices of the electronic instrumentation, microwave communications and master recording fields.
Total electronic modularity is another Spectral hallmark. With its miniaturized components and convenient plug-in circuit modules, the DMA-90 is made for quick and efficient servicing. More importantly for the satisfactions of long-term ownership, these modular circuits also permit it to be upgraded as its underlying design evolves. The DMA-90's predecessor, the DMA-80, is fully upgradable to DMA-90 specifications and performance at moderate cost and with minimal disruption of the owner's listening enjoyment.

The DMA-90 is Spectral's latest response to the distortion issues which gave rise to a generation of high-bias, Class A solid state amplifiers some year ago.
Class A works, but at considerable cost. It is very inefficient, generating large amounts of heat. Class A amplifiers require massive heat sinks and massive power supplies, therefore a larger chassis to support the whole operation. In circuit design, everything is related to everything else. Bigger parts and larger circuit configurations mean longer signal paths, which tend to radiate and interfere with one another.
The design of the DMA-90 is an exercise in taut, spare, sophisticated simplicity. The amplifier utilizes a floating bias current which follows the music signal. Because a relatively low bias is normally needed to keep the output devices within their linear range, the DMA-90 is quite efficient. It generates little heat. The DMA-90's rise and settle times are on the order of a few hundred nanoseconds - this is a few ten millionths of a second. This is well below the threshold of audibility.

Driver section. The driver section of the DMA-90 is a fully discrete, low impedance op-amp with flat signal response from DC (no frequency) to 50 megahertz. Stability over such a wide frequency range is unprecedented in an audio component. It is achieved by means of very tight, complementary and balanced circuit topology utilizing premium components. At Spectral, we believe that there is only one truly correct and optimum amplifying device for each point in the driver circuitry.

Output section. The DMA-90's output stage is a high speed follower to the driver stage. Its remarkable two megahertz power bandwidth is achieved by utilizing hand sorted output devices carefully matched for turn-on characteristics and gain. The transmission lines are as short and tight as possible, carefully impedance-tuned to the very high speed power devices. The result is a perfectly aligned output launch, free of the smallest time domain error or smearing.

Power supply. the DMA-90's power supply is stiffly regulated with a very high peak current capability to enhance the amplifier's overload characteristics. The 300 VA toroidal transformers are built to an exclusive, very compact design which, with their precision winding and custom mu-metal shield boxes, minimizes magnetic flux fields and maximizes regulating effectiveness.
The filtering section of the power supply employs new generation, low ESR, very high speed filter capacitors with several times the peak capability needs of the DMA-90 amplifying section itself.

Grounding. Grounding is one of the most important - if lest appreciated - aspects of audio design, especially for a very fast, ultra-wide bandwidth amplifier like the DMA-90. Imperfect grounding can create serious noise and distortions which affect more than the power amplifier alone. Problems can be propagated back through cables to degrade the performance of other audio components as well.
The DMA-90 employs star grounding techniques to eliminate electromagnetic and electrostatic interactions within the music system.

The DMA-90 is built to all applicable military and NASA specifications for parts quality, PC board fabrication, assembly and soldering. Selected stainless steel hardware, high purity copper conductors and high current gold plated connectors are used throughout. One percent metal film resistors are standard except where handmade, bulk metal film Vishay resistors are used in sensitive circuit positions. The lightweight, high quality aluminum chassis, with its Class A Polane paint finish and handmade, hand ground heli-arc welded seams contributes to the DMA-90's sonic performance by eliminating hysteresis, eddy current effects and the arcing which sometimes results from anodizing. The front panel is milled from solid imported Swiss stock and glows softly with Spectral's unique natural camera finish.
Every DMA-90 is burned in for 400 hours with power cycling every six minutes, a stabilization procedure unparalleled in the audio industry. Every unit is regularly checked for quality adherence and specified performance during burn-in, and subjected to a careful personal listening test before being approved for shipment. The result: unchanging sonics over the very long life of the instrument.
The DMA-90 is the amplifier of choice for speakers which present a complex load, such as fine electrostatic, hybrid and ribbon speakers. How an amplifier starts and stops - how quickly it stabilizes itself from inevitable overload - is especially important with speakers such as these, which react strongly, capacitively and inductively, with the amplifier driving them.
Professionals look for overcapacity in their equipment, both in terms of ruggedness and performance. In rigorous pro-sound applications and for monitoring recording sessions, Spectral's compact amplifiers are found throughout the world.
The power amplifier is the penultimate component in the audio chain. A good amplifier must power and control the loudspeakers and preserve the inner detail of the music without artifact. It must amplify the music signal as cleanly and accurately as possible, and also deal with energy reflected back to it from the loudspeakers while not radiating interference back towards the signal source driving it.
The DMA-90 is as "transparent to the source" as we think a power amplifier can be. By banishing modulation noises and providing the most linear, distortion-free signal gain possible, the DMA-90 permits individual voices and musical lines to emerge from a quiet, natural ambience with exceptional clarity.
Technology is the means, but at Spectral our success is in making the technology disappear. Sit back and enjoy the music.

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