Spectral historia

In 1982 Spectral engineers pioneered the industry's first wideband, high-speed audio power amplifier. The Spectral DMA-100 Class A Instrumentation Amplifier marked the origins of Spectral's unique fast-settling fet amplification topology and, in concert with the innovative DMC-10 Preamplifier, formed the first high-speed, high-resolution audio component system. Almost eighteen years later, Spectral's precision approach to component system design continues to evolve and receive wide acclaim as the ultimate in signal accuracy and realism. High-speed amplifier technology was first made practical by the DMA-100 Class A amplifier and all subsequent Spectral amplifiers draw their basic engineering inspiration from this original benchmark design. To commemorate the introduction of the first high-speed instrumentation audio amplifier, Keith Johnson and the Spectral design team are pleased to introduce the new DMA-100S Compact Reference Amplifier. The DMA-100S pays homage to the original Spectral amplifier while setting contemporary standards in musical performance and high value for the millennium.

Inspection of the new DMA-100S reveals many similarities with the original Spectral amplifier, including similar power and topologies. Although alike in many regards, the compact, cool-running design of the DMA-100S attests to the many engineering advances made since the 1980s at Spectral. The DMA-100S is actually a contemporary marriage of our state-of-the-art DMA-150 and compact reference DMA-90 technologies. Conceived by Dr. Keith Johnson as a compact reference for recording work, the DMA-100S features a magnificent combination of design elegance and convenient size mirroring the classic packaging of our SDR-2000 and SDR-3000 reference components.

As with earlier Spectral compact amplifiers, little in the restrained appearance of DMA-100S forewarns of the unusual performance potentials which exist within. For under the hood of the compact DMA-100S lurks the heart of the DMA-150 Reference Amplifier with its proprietary "Focused Array" output section design. In this premium topology, each matched output device is mated to its own power supply, including individual filter capacitors, rectifiers and transformer secondary windings. This breakthrough topology aligns high-current fet output devices for rapid, pistonic signal launch, with full rated power delivered with absolute load stability at 1 MHz. The resultant output section response capability is unprecedented in an audio amplifier of this power. Speaker control with the DMA-100S is startling, with transient and dynamic resolution of fine recordings equalled only in our most premium amplifier designs.

The high-value DMA-100S makes premium discrete circuit topologies, which were only available previously in Spectral's high-current reference designs, available for a fraction of the cost. The DMA-100S offers state-of-the-art performance, new design refinement and extraordinary value in the Spectral tradition. The DMA-100S represents the innovative thinking and quality commitment of the original Spectral DMA-100 and more. We think you will agree, some good ideas really deserve an encore.

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The DMA-100S 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-100S'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-100S speed and wide stable bandwidth are signature traits of a Spectral amplifier. So also is the 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-100S 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. All signal and power supply circuitry is designed into integrated assemblies to promote ease of revision and combat product obsolescence.

The DMA-100S is Spectral's latest response to the distortion issues which gave rise to a generation of high-bias, Class A solid state amplifiers some years 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-100S 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-100S is quite efficient. It generates little heat. The DMA-100S's rise and settle times are on the order of a few hundred nanoseconds - that is, a few ten millionths of a second. This is well below the threshold of audibility.

Anatomy of an amplifier

Driver Section. The driver section of the DMA-100S 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 optimum amplifying device for each point in the driver circuitry.

Output section. The DMA-100S'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-100S's power supply is stiffly regulated with a very high peak current capability to enhance the amplifier's overload characteristics. The 300 VA power transformers are built to an exclusive, very compact design which, with their precision winding and custom mu-metal shield boxes, 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-100S amplifying section itself.

Grounding. Grounding is one of the most important - if least appreciated - aspects of audio design, especially for a very fast, ultra-wide bandwidth amplifier like The DMA-100S. 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 the other audio components as well.

The DMA-100S employs advanced star grounding techniques to eliminate electromagnetic and electrostatic interactions within the music system.

The multiple dimensions of quality

The DMA-100S 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-100S'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-100S 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-100S is the amplifier of choice for speakers which present a complex load, such as fine electrostatics, 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-100S 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 The DMA-100S permits individual voices and musical lines to emerge from a quiet, natural ambience with exceptional clarity.
Technology is the means, but at Spectral out success is in making the technology disappear. Sit back and enjoy the music.