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AudiocRavings, by Wayne Myers:
3 - Amplifier Apocalypse

Low Amp Distortion Is Easy

Your trusty AVR has just died. You are scouring the Web for its replacement. You find a worthy candidate. It has all of the features you were hoping for plus a few you did not expect. It is reliable, all indications from other users are that it has a low failure rate. You like the brand. It looks sharp. It is designed to all the latest interface specs. Reviewers love it. Users love it. The price is far lower than you thought it would be. It looks perfect.

Then you see the distortion spec for Total Harmonic Distortion (THD) - for this discussion we will limit ourselves to harmonic distortion only - at maximum output level. It is 1%. Wow, you think, One percent distortion, can I live with that? Is that acceptable? Is that the best they can do?

Three very different questions, and the answers are, Yes, Yes, and No. Being a thoughtful person, and thinking about it for a moment, you remember that the distortion level below the maximum output power level spec can be significantly lower than that spec, and in this case almost certainly is so, and that distortion in the tiny-fraction-of-a-percent range for normal listening levels is plenty low enough for real human beings, even for a picky human like yourself.

Clipping occurs when the signal excursion is limited
by the amplifier’s power supply rails.

Could they do better? Of course, it is easy to design an amp with distortion a lot lower than that. Imagine this conversation between two amp designers working for a prominent manufacturer of audio gear...

“Hey, Horace, you look terrible, what’s the problem?”

“Hey, Pete, I have not slept in three days, I am trying to figure out how to design this amp to have distortion below one percent, Pete, and I just can not figure it out. It just can not be done.”

I promise you, that conversation has not taken place on this planet in a long time. Low distortion amp design is not all that hard. In fact, it is probably harder to build a high-distorting amplifier than a clean-sounding one. As I sneakily implied, suggesting that you already know it to be true, the typical distortion for an amp can be a lot lower than that worst-case number, which is most likely measured right at the clipping level, so a 1% worst-case spec might well translate to a typical distortion measurement of 0.1% to 0.25%, possibly even lower.

To be fair, there are many challenges in audio equipment design, and I complement the skills and accomplishments of the fine engineers who help supply us with the audio gear we enjoy. Still, I am confident that most of them would agree that getting acceptable typical distortion numbers is not the hardest part of the job. Extremely low distortion numbers might be a little harder to achieve, without resorting to measures that can actually make an amp sound worse, but accomplishing a typical distortion measurement of 0.1% range in a Class A/B amplifier would be a walk in the park.

Expensive Specifications

Then if it is relatively easy to design a linear amp with adequately low distortion numbers, why design an amp with distortion a lot lower than that? Simple. They can sell it to us for MORE MONEY!

Is a super-low distortion spec BAD? The answer, most likely, lies among the following possibilities:
  • It depends.
  • Probably not.
  • It is probably unneeded and has caused you to waste some money.
  • Who cares, if you are happy?
  • Yes, if it was achieved at the expense of another audible quality that IS easily heard. I doubt this happens often, but it probably does once in awhile.
  • Yes, if the focus upon it leads you ignore other aspects of the amp’s design that matter more.
  • Yes, if someone has managed to convince you that music played through an amp with a 0.001% distortion spec will sound better to you than music played through an amp with a 0.01% distortion spec, because, all other factors being equal, it is very unlikely that you could ever detect any difference between the two. VERY unlikely.

Latest versions of Room EQ Wizard allow the user
to add controlled distortion, harmonic by harmonic,
with settings for amplitude and phase.
Experiment. See what you can hear.
Then remember that it is MUCH harder to hear
with music.

We could go on for many pages discussing the interwoven intricacies of specmanship, audibility, and marketing in audio. The point here is that, beyond a certain point, lower distortion is just not important. You might like the idea of it, you might even think you can hear a difference (another discussion altogether), but in the reality of time, space, matter, and energy that we inhabit, it simply is not.

Good Enough

Realizing how distortion works, it becomes clear that a 1% worst-case spec translate to typical distortion numbers of around 0.1%, if not better. And that, while there might be other factors that make the amp more expensive, and other factors that might make the amp sound better, improving on that distortion spec is probably not among them. Notice I said probably. I could be wrong. I have been before.

Distortion in a Marshall Stack - GOOD.
Distortion in an audio-video receiver - BAD.

To summarize the current state of the art concerning amplifier design and harmonic distortion:
  • Most amps these days, in typical, normal use, are operating with THD levels well below their worst-case specified distortion level, and well below 1%, perhaps even below 0.1%.
  • Most good-sounding amplifiers have pretty good THD specs. It is common to see worst-case specs much lower than my 1% example, more in the range of 0.5% or 0.25% or even lower, and typical-use numbers well below 0.1%.
  • This is achieved without heroic measures on the part of the manufacturer.
  • If you go looking, you can find worst-case THD specs in the insanely-low range. IN THAT RANGE, the relationship between the lowness of the THD spec and the highness of the price will tend to become reciprocal. Lower distortion bears higher price.
  • If the idea of that lower THD spec really appeals to you, and you really want to get rid of the cash, go right ahead. Just know that the insanely low THD spec is not going to benefit you in real listening terms.
  • Chasing insanely good specs in general is a good way to put space between yourself and your cash, and to eliminate space between your cash and some amp maker.
  • Starting a column with a title like Amplifier Apocalypse, just to get the reader's attention, is a lot like claiming that insanely low amp distortion spec is your key to great sound. Only in the case of this article, it did not end up costing you anything. When buying an amplifier, it might.

Welcome to AudiocRavings, my blog of audio-related thoughts, musings, ideas, discoveries, suggestions, rants, and ramblings. With luck, a portion will be somewhat useful to someone somewhere somehow.

Wayne Myers

18 Posts
AudiocRavings, by Wayne Myers:

[*]Chasing insanely good specs in general is a good way to put space between yourself and your cash, and to eliminate space between your cash and some amp maker.

Wayne Myers[/I]

Epic common sense... so rare in the cork-sniffing hi-fi fanatics. That, (and REW) are why I joined HTS.
Thank you!
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