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BiffsBiz
205
Jul 25, 2014
10% THD at 500 Hz is audible. Is this a serious spec?
JDWarner
349
Jul 25, 2014
BiffsBizFor you and other people who seem to get hung up about stuff like this, particularly with respect to tube gear:
THD is a spec which is dependent on the output of the amp. In a better time, when ratings were more honest, amps were often rated at multiple outputs. You might have a receiver rated at 80W from 20-20kHz with both channels driven into 8 ohms that has a THD of 0.03%, and that same receiver would be also advertised at 150W for a 1kHz tone burst into 8 ohms, with one channel driven, with a THD of 1%. Today, that amp would probably be pushed to about 250W with one channel driven at 1kHz tone burst into 4 Ohms, and be sold as a 250W x7 surround sound amp. That's a complete misleading lie, but nobody's yet brought a false advertising claim because the fine print does specify how testing was done.
What you're seeing with that spec is a characteristic common to tube designs: when they get close to their limits, they distort rather than clip. This is a good thing! It sounds better to the ear (NAD had a circuit to emulate this in their SS designs for years called "soft clipping") and it also protects your drivers, which clipped waveforms are more likely to destroy.
The problem is that people today seem to care more about the number on the spec sheet rather than the quality of the components. This is how Samsung keeps selling phones, and why Best Buy keeps selling grossly over-rated surround sound amps. Worse, tube designs are generally better at driving complex loads but they put out lower power, so their manufacturers are left with a quandary: Rate their amps low, with good THD figures, or rate them a bit higher with worse THD? It turns out most potential customers weight the watt count higher, so this is often the choice made. BH opted for this when detailing the THD spec.
This is further exacerbated by the fact that "modern" designs cheat by using a lot of global feedback in order to artificially reduce the THD spec. Ergo, the comparison is not apples to apples. This does work, but it doesn't generally result in better sound; it just pads the spec sheet. Sounding familiar? The S.E.X. is a ZERO feedback single-ended triode design, which is one of the best sounding architectures in all of audio. Period! This isn't a point up for discussion; go read about SET amps and come back if you're unaware.
This kit is one of the least expensive methods on the planet to experiment with SET architecture. Those who do, rarely go back. The quoted specs, including that THD measurement, are in line with other SET amps including the vaunted 45 tube.
tl;dr - Absolutely nobody should let the THD spec turn you away.
BiffsBiz
205
Aug 21, 2014
JDWarnerThanks for the educated response. My bad.
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