The DMC-12 High Resolution Preamplifier

    The The DMC-12 High Resolution Preamplifier defines the critical importance of preamplifier performance in high quality music systems. The essential role of the audio preamplifier cannot be overestimated in its profound impact upon the performance of the electronics and transducers which follow it. Such strong influence over sonic quality is probably exceeded only by the signal source itself, making the preamplifier's role a critical link in the audio electronics chain. The audio preamplifier defines the potential performance of the system's power amplifier and loudspeakers. Compromises in the essential preamplifier link are magnified downstream and strongly determine the ultimate fidelity of the total music system.

    Awareness of the critical role of the audio preamplifier drove the formation of Spectral Audio in the 1970s and resulted in performance breakthroughs in preamplifier design. Starting with the innovative MS-ONE Instrumentation Preamplifier in 1976, Spectral has pioneered a new generation of high-resolution preamps which define the state-of-the-art in high performance music systems to this day. Design innovations such as full DC coupling, high-speed Megahertz operation and dual monaural instrumentation construction were introduced to audio in Spectral preamplifiers, and continue to define the finest products available. It is from this uncompromising tradition of preamplifier excellence and innovation that the remarkable Spectral DMC-12 High Resolution Preamplifier is inspired.

The DMC-12 High Resolution Preamplifier represents a distillation of Spectral's broad experience developing the most sonically accurate preamplifiers for the enthusiast. Spectral preamplifiers combine the oft-praised "musicality" and naturalness of the finest vacuum tube designs with solid state's frequency extension and long term reliability. More than just a synthesis of tube and solid state virtues has been achieved in the DMC-12, rather a new level of total sonic realism which transcends the strengths of both design traditions.
Spectral designers have always made a clear distinction regarding the essential role of audio electronics and preamplifiers in particular. In respecting the sovereignty of the original recording, the preamp must always be a faithful music reproducer and not a musical instrument in its own right. Audio components which artfully beautify or euphonically "improve" the sound of the recording are more musical instrument than truthful reproducer. In time, these initially attractive qualities pale in comparison with components which accurately reproduce the source and allow the true voice of the recording to be fully presented without coloration. Revealing the musical source in all its complex dimensions without subtle distortions is the design goal of the DMC-12, moreover, it is the ongoing engineering quest at Spectral.

The DMC-12 incorporates the fruits of two decades of Spectral research into time domain and phase behavior in audio circuit topologies. The DMC-12's high speed and ultra wide stable bandwidth are signature traits of a Spectral high-resolution preamplifier. These techniques combine to allow significant reduction in time based distortions which dominate the sonic character of virtually all other high performance preamplifiers.
Fundamental accuracy in audio circuitry requires more than just flat frequency response and low overall distortion in the audible range but must take into account the "big picture" of signal linearity over a broad frequency spectrum. This is because the human ear is especially sensitive to phase distortions. These out of band distortions reflect back into the audible range to blur the individual sounds of musical instruments and their distinctive acoustical space.
To solve the problem of time based distortion in audio circuitry Spectral has turned to solutions developed by the instrumentation and microwave fields and adopted their "low-pass filter" model. Achieving the most linear signal amplification modeled on the ideal of a low pass filter requires flat circuit response from DC to a magnitude above the critical bandwidth. In the case of all Spectral circuitry the signal response range extends from DC to at least one million cycles (1 MHz) at full rated power. Above this frequency a precisely tailored high-frequency roll-off (the low pass element) is then tuned to eliminate even the smallest phase reflections keeping audio frequencies pristine and transient-perfect. By designing the DMC-12 circuitry to the precise criteria of a perfect low-pass system, time-based distortion and intermodulation noise is virtually eliminated in the audio band. No other approach to audio electronics design will result in greater freedom from the vast array of distortions or allow more fundamentally accurate reproduction of music.
As with other Spectral components, the DMC-12 presents a face of simple elegance and clean purpose to the world, to discover the most important qualities one must look inside. The DMC-12 has much in common with cost-co-object laboratory instrumentation where a premium is placed on performance and component quality. Conventional consumer audio parts and design practices are insufficient to support the requirements of Spectral's ultra precision, high-resolution discrete circuitry. For this reason, custom signal devices and proprietary components are sourced from premium suppliers worldwide for Spectral preamplifiers. Component assembly and soldering quality and materials are similarly uncompromising.
Music is complex and transient in nature requiring tremendous circuit precision to track the subtleties of dynamic waveforms. The ability of the circuit to rise quickly to amplify fast moving transients and to settle virtually instantaneously is a capability uniquely developed in Spectral preamplifiers. The DMC-12 line level gain stage employs a cascode Fet front end for maximum linearity and complimentary power Mos-Fets (of a custom-made, proprietary design) as output followers. Localized feedback is used to keep overall feedback very low while providing nearly spontaneous correction of output signal errors. The line level stage exhibits a very high and symmetrical slew rate and lighting fast rise time (65 nanoseconds) combined with remarkably low overall energy storage.
The output section of the DMC-12 is a miniature class A power amplifier, including inboard heat sinks. This unusually high-current output (up to one-half ampere per channel) is a result of Spectral's research into the difficult demands made by complex, high quality interconnect cables and sophisticated, low impedance power amplifiers. The DMC-12's high current output capability allows it to dominate and control the cable and amplifier load, making it self-isolating from the effects of system energy storage and reflections.
The DMC-12 is supported by the powerful DMS-12 Supply which produces output voltages typically associated with tube preamplifiers. As a result, the DMC-12 is characterized by a sense of total openness, lack of strain and crystal clear dynamic resolution at both low and high listening levels.
In Spectral preamplifiers the gods do "live" in the details. So in addition to fundamentally superior signal response, every detail of the DMC-12 circuitry has been lovingly tuned, optimized and refined for the highest musical resolution and long-term stability. The straight-line signal topology reflects a philosophy of high performance and purist design. No higher quality componentry and construction are available in a preamplifier today. The elegant functionality of the modular DMC-12 system proclaims high value and freedom from obsolescence which is all too rare among audio components. As the essential centerpiece of the finest available music systems, we believe you will accept nothing less.

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