I'd had my Spectral DMA-90 amp for about 3 years (also a DMC-12 preamp) when I first saw the DMA-100S amp at the Spectral dealer for the Chicago area (entire midwestern U.S.A.?--there were about 14 in the country). I then asked the dealer "Does this mean I really should upgrade to the new DMA-100S?" He thought for a bit less than a second (probably analyzing my emotional state of the moment), and answered (to his credit; he is a good person and still in business but hasn't been a Spectral dealer for years): "No, what you have now is fine."
I wandered around the store for a while in a confused, conflicted state: I was a big believer in "the latest and greatest", and I always expected to and was fine with upgrading my Spectral gear if financially feasible--but just not so soon! Eventually, I spoke with one of the dealer's part-time employees, a college student, about this.
He answered me: "I just work here--not an owner--and have no strong financial interest in whether you purchase a new amp. I hear both amps in the course of my workweek. I have to tell you, the DMA-90 sounds better to me." He then said something to the effect that, with the DMA-100S, it seemed as if there was something going on "behind the scenes" (as if it were doing more? working "harder"? working "differently"?) as it created the amplified music signal. It almost seemed that he was implying that the DMA-90's amplification of music signals was more "organic".
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According to the Spectral Audio website, the specs on the two amps are nearly identical. The following seemed to be the major differences (unless these are typographical errors):
DMA-100S:
Noise:
Signal to Noise:
90dB unweighted, 107dB ASA A
Crosstalk:
80dB @ full power 8 ohms
DMA-90:
Noise:
Signal to Noise:
97dB unweighted, 107dB ASA A
Crosstalk:
98dB @ full power 8 ohms
Might these differences have accounted for (some of) any perceived difference(s) in sound between the two?
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A final question: As other(s) have written, there is not much info about the DMA-80 amp. People like the DMA-50 and DMA-90 amps--the DMA-100S, it seems not as much. But, according to Spectral Audio, all three of these have a slew rate of 1000 volts/microsecond. (How unusual it seems for an amp to have the same slew rate as the company's preamps!) Some of Spectral's latest amps, such as the Spectral DMA-300SV Reference Standard and the DMA-400 Monaural Reference Standard, claim a slew rate of "only" 650 volts/microsecond. (The DMA-300SV's bulletin [0319] claims it is their "best performance to date.")
Could the high slew rate of the DMA-50 and the DMA-90 be responsible for their much-liked sound? Hopefully, forum members much more knowledgeable than I will share their thoughts on this--and, also, regarding how high a slew rate is "enough" to reach the Spectral level of audio performance!