Very low THD DAC/AMP makes no sense, as transducers are the primary source of distortion.

[wolfield]

Consider the following: high-quality modern electroacoustic transducers (speakers or headphones) can achieve distortion figures in the ballpark of 0.1% (-60 dB), and this applies to really good units.
Now, imagine two DAC/AMP combos that deliver 0.01% (-80 dB) and 0.0001% (-120 dB) distortion to these high-class speakers with 0.1% distortion.

Right away, there is a catch regarding the difference we can expect from both systems. Harmonic distortions from different components in an audio chain do not simply add linearly in a straightforward way (e.g., -80 dB + -60 dB does not directly result in a single combined dB value). In most real-world scenarios, the phase of the distortion components is not perfectly aligned, so we treat them as uncorrelated signals and combine their power (not amplitude). However, let's imagine an absolute worst-case scenario and assume that harmonics are perfectly in phase, so we add distortion amplitudes directly.

For -80 dB playback system:
Convert dB to Amplitude:

• DAC/AMP: -80 dB = 10^(-80/20) = 0.0001
• Speakers: -60 dB = 10^(-60/20) = 0.001

Combine amplitudes directtly for the worst-case scenario:

• Total amplitude = 0.0001 + 0.001 = 0.0011
• dB level = 20 * log10(0.0011) = -59.17 dB

For -120 dB playback system:

• DAC/AMP: -120 dB = 10^(-120/20) = 0.000001
• Total amplitude = 0.000001 + 0.001 = 0.001001.
• dB level = 20 * log10(0.001001) = -59.99 dB.

And here we have it, folks - hardly any improvement of only 0.82 dB.
What's worse - the real-world number will be even lower.

 

[wolfield]

And if we combine distortion powers using the root-sum-square method, which should be much closer to the real world than our absolute worst case scenario then the difference between -80 dB and -120 dB playback systems on -60dB THD speakers will be around 0.03 dB only.
This is absolutely negligible, comparable to measurement inconsistency.

Until technology allows the production of speakers/headphones with distortions lower by an order of magnitude than the current generation of transducers, the pursuit of very-low distortions in the audio chain is akin to literally applying snake oil to your forehead.

 

[NTK]

As many here are engineers, we celebrate execution excellence. The recent SMSL SU-1 DAC achieves a SINAD of 116 dB for a current retail price of USD $85 at Amazon. What is the excuse of doing worse than this if you're asking for more money? If your device comes in with auto DSP, I'll give you a 10 dB discount for processing headroom.

Given the level of performance already baked into DAC chips, what are the reasons for a final product to perform worse than the reference design? Ditto for amplifiers.

 

[Waxx]

Both of you are right, and the only excuse to do less good than those cheap is a deliberate colouration, sometimes with old tech (tubes, class A). But then don't claim a superior sound on tech level when you build that kind of amplifier. Technically they are inferior, but that does not mean people will not like it. Oldtimer cars (or cars build the old way like Morgan cars) are also technical inferior to modern cars, but they are still fun to drive and have a certain feel that modern cars can't give.

First Watt amps (mostly class A) are not getting there, because they were designed with a certain colouration in mind that the designer (Nelson Pass) intended. He doesn't sell them as technical superior, he sells them as a niche amp with a colouration that he likes and he knows most of his customers like. He said himself (on diyaudio) that if you need super clean amps you better look elsewhere, beause he doesn't make them. He finds them boring (he finds... so subjective).

But if you ask 10K or so because "your amp is superior", and then it measures at 80dB sinad or has other deviations from the technical standards of hifi, then you're selling snake oil because better amps can be had for a few hundreds, or maybe even less.

 

[Mnyb]

We also have noise and FR response . The "usual" design methods that yield low thd tend to also yield low noise and very flat FR and in power amps also low output impedance ?
So they sort of go together ?

 

[Mnyb]

And it does not seems to hard to accomplish . "Bad" data in moderns amps tend to be because of deliberate incompetence using "alternative facts" when designing

 

[Head_Unit]

Harmonic distortions from different components in an audio chain do not simply add linearly in a straightforward way

Well while I think you have a good point, the distortions are not even always the same. And the ear is quite sensitive-I remember having to search out an old time analog signal generator to run woofers in free air because the (inexpensive) digital stuff all sounded like the woofer was rubbing or something. I also don't like the conflation/mixing here of raw noise with distortion so color me firmly in the "SINAD is not god" camp.

I suppose that is a separate issue: I agree since way back in the early Japanese transistor days that crazy low distortion numbers are meaningless, particularly if they come at the expense of other aspects of performance. We still measure only a very limited set of numbers with regard to amplifiers. In audio we measure nothing transient, for instance, certainly not into complex loads. Everything is measured steady state, and even "impulse" response etc are just calculated from...steady state measurements!

 

[NTK]

...
I suppose that is a separate issue: I agree since way back in the early Japanese transistor days that crazy low distortion numbers are meaningless, particularly if they come at the expense of other aspects of performance. We still measure only a very limited set of numbers with regard to amplifiers. In audio we measure nothing transient, for instance, certainly not into complex loads. Everything is measured steady state, and even "impulse" response etc are just calculated from...steady state measurements!

Quoting Doug Self (once again) ...

"Sinewaves are steady-state signals that represent too easy a test for amplifiers, compared with the complexities of music."​

This is presumably meant to imply that sinewaves are in some way particularly easy for an amplifier to deal with, the implication being that anyone using a THD analyser must be hopelessly naive. Since sines and cosines have an unending series of non-zero differentials, "steady" hardly comes into it. I know of no evidence that sinewaves of randomly varying amplitude (for example) would provide a more searching test of amplifier competence.​

I believe this outlook is the result of anthropomorphic thinking about amplifiers; treating them as though they think about what they amplify. Twenty sinewaves of different frequencies may be conceptually complex to us, and the output of a symphony orchestra much more so, but to an amplifier both composite signals resolve to a single instantaneous voltage that must be increased in amplitude and presented at low impedance. The rate of change of this voltage has a maximum set by the frequency response and amplitude capability of the channel and is not generally greater for more complex signals; you do not get hgher slew rate with bigger orchestras. You must remember that an amplifier has no perspective on the signal arriving at its input, but literally takes it as it comes.​

​

 

[valerianf]

I would add that there is another source of distortion: the inability of some amps to drive the real world speaker load.
I just replaced a Yamaha RX-A700 with a Onkyo TX RZ30.
It is night and day for driving two large tower speakers and a center.

 

[delta76]

Consider the following: high-quality modern electroacoustic transducers (speakers or headphones) can achieve distortion figures in the ballpark of 0.1% (-60 dB), and this applies to really good units.
Now, imagine two DAC/AMP combos that deliver 0.01% (-80 dB) and 0.0001% (-120 dB) distortion to these high-class speakers with 0.1% distortion.

Right away, there is a catch regarding the difference we can expect from both systems. Harmonic distortions from different components in an audio chain do not simply add linearly in a straightforward way (e.g., -80 dB + -60 dB does not directly result in a single combined dB value). In most real-world scenarios, the phase of the distortion components is not perfectly aligned, so we treat them as uncorrelated signals and combine their power (not amplitude). However, let's imagine an absolute worst-case scenario and assume that harmonics are perfectly in phase, so we add distortion amplitudes directly.

For -80 dB playback system:
Convert dB to Amplitude:

• DAC/AMP: -80 dB = 10^(-80/20) = 0.0001
• Speakers: -60 dB = 10^(-60/20) = 0.001

Combine amplitudes directtly for the worst-case scenario:

• Total amplitude = 0.0001 + 0.001 = 0.0011
• dB level = 20 * log10(0.0011) = -59.17 dB

For -120 dB playback system:

• DAC/AMP: -120 dB = 10^(-120/20) = 0.000001
• Total amplitude = 0.000001 + 0.001 = 0.001001.
• dB level = 20 * log10(0.001001) = -59.99 dB.

And here we have it, folks - hardly any improvement of only 0.82 dB.
What's worse - the real-world number will be even lower.

you are missing the point.
your SINAD will be dominantly affected by the weakest link in your system, i.e. the component with lowest SINAD. If one more component of your system has a transparent SINAD, you have one less thing to worry about.
And then you have EQ/Room correction, lower SINAD means harder to EQ

 

[CuteStudio]

My experience is that speakers and amplifiers work together, and many 'good' amplifiers simply don't cut it.

For example, some old KEFs I have B139/B110/Tweeter - so a 'not easy' but 'not difficult' to drive speaker, of medium efficiency - were driven from an early Cyrus One. This was then switched out for some Hitachit/Maplin MOSFET amplifiers with beefy PSUs and the sound was instantly more solid, even at power levels well within the range of the 'amazing' Cyrus/Mission amp. The Nad 3020 was the same - all very good, but not 'that' good.

With these speakers I have good sound also with a 150Wpc Class A Usher R1.5 (a Threshold increment IIRC) and my Single Ended Pentode amp.
Some of the best speakers I've heard are the Grundig Box 550 - beautifully transparent sound.

So I do view speakers as the most important for sound, but amplifiers, although many claim they all sound the same, I have mathematical reasons and experience - that they make a big difference .

It's also my experience that beyond a certain point, throwing more money at speakers and amplifiers results in a far worse sound - some of the most horrible sounds I've heard some from eye wateringly expensive systems.

Turntables, cartridges and to an extent arms seem to be all over the place.
DACs - I have my Apple USB-C headphone DAC, sitting on an upgraded USB isolater that gives it a new, flat, smooth PSU, and have yet to hear anything else at any price that sounds better to me.

Cables - I'm a big fan of Car Audio cables and a soldering iron. Car speakers are 4ohm and the car guys are into lots of power, so the speaker cables can be bought off the roll in fantastic quality - without getting scammed.

Cable scams, the Loudness War and the refusal of the music industry to release high quality unclipped digital formats (they knobbled the SACD) are IMO the cause of the death of mainstream hifi. I.e. it was killed by greed, which is a shame.

But today Bluetooth boombox speakers are bringing it back - ironically. Today in department stores and supermarkets (not british supermarkets, but continental ones) bluetooth speakers will be found - and people are buying them. Ruark make some nice ones, Naim is trying hard, JBL, Marshall's Woburn III was quite passable, and a bargain I found in France - the MUSE M980-BT which sounds remarkably good (with midrange Magico can only dream of) - is weaning people away from stupid earbuds and back to rooms full of sound again. Buy two of these bluetooth items and you get stereo splitting too. Bluetooth used to suck for music - but the lastest version seems Ok.

So I guess the most popular hifi will soon be, or is, combined speaker, amplifier and DAC.
For older stuff, DIY tweaks and parametric EQ can squeeze a lot more performance from them.

So I agree - my DAC spend is £9 for the DAC, £10 for the USB isolator + £5 for an upgrade PSU module -> £24.
Oh and a posh cable from eBay, 3.5mm to RCA, gold plated (or at least, gold coloured LOL) for about £4.
It sounds divine.