Hi Burke,
Here is a more technical explaination for you on your first watt question.
I have been asked a few times what Bryston means by 'super-low distortion from the first Watt'. Simply stated, this means Bryston amplifiers, (and the new 28B SST is the prime example), do not have annoying high-order harmonics that get worse with descending power levels. Class-AB amplifiers have often been found to have high-frequency artifacts that become a larger percentage of the overall distortion picture at lower power levels. Bryston's proprietary circuitry, however, eliminates this possible problem, and results in amplifiers that sound smooth and sweet from the very lowest power levels all the way to thunderous outputs that threaten to 'raise the roof'.
Over the years, tube circuitry has often enjoyed a reputation for sounding deliciously smooth, especially at low levels. This is because tube circuits typically show their lowest distortion at the lowest output levels. Bryston's new amplifiers have acquired a reputation all over the world for being 'tube-beaters' in that respect, albeit with much higher potential power levels and lower overall distortion in any power range.
First, Bryston's proprietary Quad-Complementary output circuit responds faster and more accurately to high audio frequencies than any other type of output circuit. As a result, even at higher output levels, THD at 20KHz is well under 0.005%, and vanishes into the unmeasurable, below the low noise levels, at 1 Watt.
Second, Bryston's super low-noise input circuitry removes the final veil from low outut levels and faithfully reproduces the dynamic range of the original performance. The 28B SST, for instance, measures typically more than -115dB from 20-20KHZ, Unweighted.
Third, Bryston's power-supply design prevents interchannel crosstalk, and preserves the exceedingly subtle directional-cues, image placement and 3-dimensionality of the original performance better than any other amplifiers we have heard, akin to a 'sonic hologram'.
Sincerely,
Chris Russell
CEO, Bryston Ltd.
James, thank you for getting the more detailed technical explanation and thanks to Chris Russell for providing it. Those points taken together help explain why music played through Bryston amps sounds so remarkably "real", and listening at just about any volume for extended periods is not fatiguing.
Burke
So, do you agree or disagree with this?
Although this is not intended to be an exhaustive examination of all available semiconductors or tubes, the resulting frequency spectra lead us to some conclusions that experienced audio designers have often remarked upon in the past.
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Transistors operating on low-voltage supplies tend to have higher spectral distortion components than tubes.
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If we go to high-voltage transistors, operating on supplies comparable to those of the tubes, the distortion products are less objectionable. Unfortunately, the noise floor of such devices is much higher. The IRF822 was very triode-like in distortion yet suffered from a noise floor some 30 dB higher than that of the triode.
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No other active device possesses both the low distortion products and the low noise floor of the medium-mu triode—albeit at the expense of voltage gain.
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The distortion products of transformers are much lower than those of active devices, yet quite different in character. Note that the odd-order harmonic products tend to be higher in level than the even-order products—exactly the reverse of the tubes and transistors.
It should be obvious that these simple circuit designs can be improved upon, by using differential topologies with constant-current loads and negative loop feedback.
It should also be obvious that the same techniques can be applied to transistors or to tubes; and if this were done, the triode would continue to enjoy some advantages over the semiconductors—and the pentode, for that matter.
—E.B. with John Atwood
Hi James;
No, I don't agree with all of it. My earlier post was pretty specific on the various agreements and disagreements I have with Mr. Atwood, but to recap: Tubes and transistors are both capable of very good performance if implemented properly. However, tube amplifiers have tended to display much higher THD (and noise), than solid-state amplifiers, partly due to the lower gain of tubes. That requires extra comlexity in a tubed amplifier for similar power, gain, and other parameters. Soilid-state amplifiers when correctly designed and constructed display vanishingly low distortion, noise, and especially do not contain higher-order harmonics in their distortion spectra.
I do not consider the presence of an output transformer in a tubed amplifier to be a performance disadvantage. Transformers can be remarkably clean and linear in their performance, and especially when included in the feedback loop, can work within a tubed amplifier to deliver excellent measured performance in all respects. It does add to the overall cost and complexity, of course, again giving solid-state amps a substantial advantage in those respects.
Having said the above, I can agree with Mr. Atwood's statement,
'It should be obvious that these simple circuit designs can be improved upon, by using differential topologies with
constant-current loads and negative loop feedback.' Unfortunately for tube-amplifier aficionados, the above is not generally part of tubed amplifier design, and thus most have very substantial problems with noise, IM and THD in comparison with solid-state designs.
The advantages and disadvantages of tubes vs. transistors do not disqualify either approach, but truly unimpeachable performance is a very, very difficult thing to obtain in either case. It requires an extremely thorough understanding of all the operating parameters of the chosen approach. Bryston's long investigation into the art and science of audio amplification has shown us that solid-state circuitry can deliver the best performance in a much less costly and less complex package, and does not suffer the problem of constantly- deteriorating performance with age.
cwr
