Spectral DMA-50 Amplifier - Made in the USA

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Very simple design and operation, yet built to the highest quality standards we have ever seen.  I'm talking laboratory instrument quality with regards to component selection, layout, and design. 

One of the few amps worthy of interior shots and a plexiglass cover.  Notice the gold plated circuit board and the methodical component placement and wiring paths.  

Simple operation containing only the most critical adjustments. Just power and mono/stereo operation. 

Great condition with no significant scratches or dents.  Tested fully in our lab and woking to specification. MSRP $2,999.00

See the matching Spectral DMC-10 preamp we're selling for an amazing combo. 

Comes inoriginal box with foam interior packing.  Outside of box is a bit worn but sturdy.  

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