[QUOTE="Helom, post: 32394540, member: 71602"]I suppose if I was specifically seeking a lightweight class D amp then I would probably give the Atmasphere model a try. I suspect most class D manufacturers are more concerned with cost savings and size rather than sound quality.[/QUOTE]
A good number of them are trying to get them to perform and sound as good as is possible.
[QUOTE="Richard Austen, post: 32397198, member: 53502"]I think the mistake you're making here is that as mainly an engineer you are looking at this from an engineer's perspective in that SET will go away because it doesn't measure as well as class D (or in your opinion, SET doesn't sound as good).
...Someone like me will come around to class D simply because I don't really care that much about the technology - I care about what I hear. Gear is not the point - Music reproduction is the point. I just see history illustrating whether it is audio, politics, automobiles, etc that the best doesn't always win. Lastly, I think really good-sounding Class D will also need to come from one of the big boys like Yamaha/Denon/Marantz/Sony to generate a larger foothold.[/QUOTE]
I am saying that tube power is on borrowed time because you can get all the best of the tube sound without the downside, combined without the weaknesses (brightness and harshness) of traditional solid state. So I see your opening comment above as a red herring- its not my assumption nor what I said or think. Class D is already here big time and all the big players are on board. So its foothold is enormous.
[QUOTE="Helom, post: 32397328, member: 71602"]I have yet to encounter a class D amp that doesn’t sound “thin,” regardless of specified power, or whether it’s a hybrid or employs a linear PS. It’s weird.[/QUOTE]
The simple answer here is you've not heard them all. Class D amps vary in sound quite a lot, more than tube amps do. Many of them really did have troubles getting the bass right, because they really didn't understand that the power supply really does have to be robust. The idea that they can skimp on that because the idle current is so low got them in trouble.
[QUOTE="Ampexed, post: 32397584, member: 143818"]The problem is that SET sounds the way it does because of its technical imperfections. No class D amplifier designer is going to deliberately make an amplifier which intentionally distorts the signal to the extent that an SET does (the company I work for makes a whole line of class D amps from mid-high end to very high end). Class D can and does sound just fine, but it cannot sound 'just like an SET' because the two types of amps are playing by radically different playbooks. That difference in sound is going to appeal to people with different priorities.[/QUOTE]
SETs sound the way they do because of their distortion. We didn't make our amps to have the distortion of SETs and they don't. But- like SETs, the distortion our class Ds make is mostly the 2nd and 3rd harmonics, with enough amplitude (also like SETs) to mask the higher ordered harmonics. Where its different is that overall the distortion is way lower than any SET, so it sounds more transparent. But it does so without harshness or brightness of any sort- and very good bass. Also like an SET it has a very good first Watt. How it differs in another way from SETs is the higher ordered harmonics don't show up at slightly higher power levels to cause the amp to sound 'dynamic'; IOW it does not have distortion masquerading as 'dynamics' as all SETs do at higher power levels (anything about about -6dB of full power).
Once you know the 'dynamics' of SETs is really just distortion it kind of wrecks it. So our class D is a lot more satisfying in that regard.
[QUOTE="Helom, post: 32400289, member: 71602"]Unfortunately most class D doesn’t work that way. The topology seems to distill the sound to a thin/lean presentation regardless of what’s upstream. This is especially true at high playback levels where many class D amps just “fall apart” despite their claimed power output.
It’s most apparent with the IcePower and older Hypex modules. Seems it’s still true with at least some of the GaN Fet designs also. Seems it has something to do with how they perform when asked to drive a real dynamic load as opposed to a simulated load.
[/QUOTE]
This statement is false. The real issue is one I pointed out just above: Class D power supplies must be really robust; if not, they will have troubles with bass and might sound dry. This is one area where many class D amp producers skimp out. Its not a problem with the technology as it is the intention of the producer- are they trying to make a buck or are they trying to make a nice amp? The two are vastly different!
[QUOTE="Ampexed, post: 32400846, member: 143818"]Low bass is actually the Achilles heel of class D. They cannot take sustained periods of supplying close to DC levels of current, which is why they are typically rolled off before they have to pass the infasonic region of bass. If they used large heatsinks that would be less of an issue, but then the size, weight and cost advantage of class D would largely go away.[/QUOTE]
This statement is also false. If the amp is designed properly they can sustain current no worries. For example, our amp is rated 200 Watts into 4 Ohms. You can drive it with a sine wave at any bass frequency into that impedance and the amp will sit there and do it all day long- as long as you want with no worries whatsoever. Heatsink design is critical but its not a size thing as best I can make out. Our heatsink is also the mounting method of our module and so isn't any larger than the module itself. Yet the amp has no problem making current up to the limit of the supply itself. So it makes bass as good as any amp I've heard.
This isn't rocket science. What isn't understood well in high end audio is that its driven by intention rather than price. This means good sounding products can be inexpensive, but it also means that you can do what is needed to make a circuit work the way its supposed to. Again, in a class D, the most common sin I've seen amp producers do is they skimp on the power supply. That results in everything you said. But that's not a weakness of the tech, its a failing of the person that's trying to save a buck. It results in failure.
As for rising THD versus frequency, I haven’t experienced a refinement of treble with linear THD across the spectrum. Properly designed SS has been overall terrific in the upper registries over the last 2 decades. Pass labs, benchmark, and purifi all have terrific top end and all of them have rising THD versus frequency.
@cloudsessions1 Just so you know, this statement is false. Most self-oscillating class D amps, such as the Purifi, do not have rising distortion with frequency. Where ever you got that your source is wrong.
Regarding this comment:
Humans are inherently bad at hearing harmonic distortion don’t take my word for it there’s many blind tests you can do online to see how much distortion it takes before you notice.
This test is probably not done with attention paid to distortion rising with frequency- and in that context your statement is correct. Most of the online stuff I've seen does not have that built-in to the software. So its not the same thing. When distortion rises with frequency, it puts emphasis on higher ordered harmonics. This is at the root of why solid state has had a reputation for being harsh and bright, and also why feedback has gotten a bad rap in high end audio (because it can mess with a tube amp in a similar fashion).
I've already described how Gain Bandwidth Product causes the rise in distortion with frequency. What I've not mentioned in this thread so far is how feedback is usually applied in amplifiers so that the feedback signal itself gets distorted before it can do its job mixing with the incoming audio signal. As a result higher ordered harmonics and intermodulations are created because the feedback node is not linear. Norman Crowhurst (a well known audio guru of the late 1950s and 1960s) wrote about this over 60 years ago, but almost nobody really did anything about it.
You can apply feedback without distorting it. That is done the way opamps do it, by mixing the feedback with the audio signal using a resistor network at the input of the amplifier, rather than inside the amplifier. Resistors are far more linear than any tube or transistor! We've employed that technique in our smaller OTLs for decades now.
