Competitive class D amp suggestions

For the Atma-sphere class D amp: Is a preamplifier necessary if only connecting a streamer/DAC to it? The streamer/DAC has it’s own volume control (if I want to enable it). Lumin S1.

@veerossi 

Most digital products can drive it directly with ease.

Other than heat and efficiency, what do you think are the pros/cons of moving to this amplifier from an 805 tube amp (Line Magnetic LM-805ia)?

Its my opinion that the specs listed on the Line Magnetic website are suspect. At such high power levels its very hard to make an output transformer that will support that kind of bandwidth and be SET at the same time. At any rate, you'll likely appreciate the extra power, and if you are using a high efficiency speaker you'll appreciate the lower noise floor of the class D as well. My speakers are 98dB and I have to have my head in the midrange horn to hear any noise from the amps at all. That translates easily to better low level detail, assuming that the amp has all its other ducks in a row.

Its not going to be as lush but its not dry. It won't be as lush because its distortion is so much lower. The advantage is there is more musical detail and it does this without brightness. Distortion obscures detail, and its a simple fact that whether they admit it or not, before the onset of clipping nearly every SET made makes about 10% distortion. What this means is that any any power level an SET can make, the class D is going to be well over 2 orders of magnitude lower distortion- and so at any power level will offer more musical information.

Its not dry because the distortion it makes is very much like that of a tube amplifier- with the 2nd and 3rd harmonics being far more prominent than the higher orders, but of course all at a much lower level than you can get from a tube amp. That is why I ended the last paragraph the way I did- this stuff is easy to hear.

One thing I’m still not clear about is why people describe class a and high bias a/b as being warm sounding especially if their overall distortion is on the higher side?

The distortion can be quite low! The tricky bit is knowing what is meant by 'warm'; to some this is a bit of extra mid bass energy. I see it as 2nd harmonic and of course it can be both. I think you'll find though if you delve deeper that those comments do not apply to all. Nelson Pass is aware of how distortion affects tonality so he is careful in his designs to make sure he's got a bit of 2nd going on to help out in that regard.

I still am not sure about some basic things. Now i suspect that the "higher order harmonics" are not second and third order  harmonics but 4th, 5th etc order harmonics (just to clarify, in my earlier posts i referred to "higher order harmonics" as the second and the third order ones!). Do 4th, 5th etc order harmonics also exist? Is the goal then to suppress 4th, 5th etc order harmonics with the second and third order harmonics, or also suppress the first order harmonics ? Why a high distortion in the first order harmonics cannot suppress the  4th, 5th etc order harmonics?

Let's be clear about something: 'masking' is where a louder sound (like a 2nd harmonic) can obscure a quieter sound (like a higher ordered harmonic). "Supress" suggests reducing the harmonic. So the lower orders do no suppress higher orders, but they can mask them if their amplitude is high enough in relation to the higher order(s) to be masked.

The higher orders are the 5th and above.

Are you saying that by obscuring the details greater transparency is reached ? 

No. I am saying that with lower distortion there is greater transparency; distortion obscures detail.

@twoleftears Interesting. That 18th harmonic (9KHz) looks increased. There also appear to be some intermodulations present (inharmonc; not positioned directly on a graticule or directly in the middle of two graticules). 

What can you say, generally speaking about the distortion make up for class A and highly biased Class a/b solid state amplifiers? Are they generally the higher distortion 2nd harmonic type or the lower distortion 3rd harmonic type.. or have I missed the mark completely???

Most of them tend to have unmasked higher ordered harmonics at a low level, and because the ear uses the higher harmonics to sense sound pressure, its keenly sensitive to their presence! Also because the ear assigns a tonality to all forms of distortion, this causes most of said amps to sound harsh and bright even though they might have less higher ordered harmonics than a tube amp! This is how important the masking that the 2nd and 3rd provide can actually be.

The reason so many class A and AB solid state amps have this issue is they lack the required Gain Bandwidth Product to support their feedback at all frequencies. This is why they can play good bass, since at those frequencies the feedback is enough to do the job. But at some higher frequency the amp runs out of GBP and so the feedback decreases: and with it the distortion at those frequencies rises. That is why distortion vs frequency is an important measurement. The distortion simply should not rise at all if brightness and harshness is to be avoided.

There are a few A and AB amps that appear to have enough GBP to get around this problem and I think most of you know of one of them- the Benchmark- but you still have the issue of the distortion spectra itself. Most of the measurement guys that poo-poo subjective listening will tell you that the distortion is inaudible if about 100dB down. I personally doubt that; if it were true there would be no controversy around the ’sound’ of these amps. Since getting the distortion that low (< 0.005%) is pretty hard you can see that the distortion spectra still plays a role.

One thing to keep in mind is that the distortion spectra at 1 Watt doesn’t tell the whole story! A classic example is SETs, which at lower power really do quite well. But when you get over -6dB of full power the higher ordered harmonics become more prominent. This causes the amp to sound ’dynamic’ at first (as power is increased) since the power needed is on the transients. So the ear reacts to the loudness cues on the transients, converting the result to ’dynamic’. I’m convinced that when audiophiles use the word ’dynamics’ to describe what they hear in an amplifier or stereo, that you can safely replace that word with ’distortion’ and not change the meaning of the conversation at all.

In many class A and AB amps what happens is not quite the same- as power is increased the distortion spectra changes but the result is more harshness and brightness, since that’s a problem with them even at lower volumes.

So the situation is not completely hopeless. Ralph, how these distortion parameters reflect the distortion of the harmonics of each degree?   I think that now i know that i am looking for an amp with small first order distortion but large second and third order distortions, roughly. But, as I have also mentioned, i don't really know how large they can or should be, no idea at all.  

In a nutshell, if there's enough lower ordered harmonic distortions, they can mask the higher orders. The higher orders otherwise cause harshness and brightness. Either the 2nd or 3rd can predominate, but if the 3rd dominates then it has to be at a lower level to begin with- about 1/10th what you might see if the 2nd were dominant in the design.

For example almost any SET makes 10% THD at full output- most of which is the 2nd harmonic. If you have an amplifier design that makes the 3rd instead of the 2nd (which can happen if the amp is fully differential and balanced, since even orders are cancelled throughout the design) then the THD will and must be much lower. This isn't that hard to achieve since a design that exhibits a dominant 3rd harmonic will tend to have less distortion overall anyway.

On top of that the distortion cannot rise as frequency is increased, which is a problem with most solid state amps made (and with tube amps employing feedback). Class D offers a solution for this- you can have the distortion vs frequency look like a straight line, and you can run a lot of feedback at the same time. In this way you can achieve distortion levels that are several orders of magnitude lower than you might see in a tube amp ye the actual distortion signature (2nd and 3rd vs the higher ordered harmonics) can look quite similar to a tube amp.

This allows greater transparency (since distortion obscures detail) yet the same kind of smooth mids and highs you associate with a really good tube amplifier- IMO, the best of both worlds.

In case you don't get my drift, I'm drawing a very straight causal line between the distortion measurements and how the amplifier actually sounds; IOW its predictable based on sufficient measurement! The tech to do this really didn't exist 40 years ago but it does now. A lot of audiophiles don't know that yet; like so many industries tradition plays an enormous role in this.

Electric engineers succeed to develop exceptionally sounding equipment, but the existing parameter for measuring their ``distortion'' seem to me to be useless. 

Engineers have other measurement tools: distortion vs frequency (rising distortion is an indication brightness and harshness may be present), distortion spectra at one Watt and also at 06dB of full power and distortion spectra measured at different frequencies.

If you know what you are looking for, these measurements can tell you how the amp will sound. I agree THD isn't a good marker.

I am very sad that Ralph’s Class D is designed only for Nth America and Canada (and perhaps a few others) electricity supply, otherwise I’d be placing my order.

@noske We recently documented that our noise emissions meet EU directives; we always had intention of selling overseas.

https://forum.audiogon.com/discussions/rip-tom-o-brian-of-the-cherry-amp-co

@niodari Sorry, Tom passed away last December.

this is what I always wanted to hear!  It only remains to experience it unless it is taken as faith

@niodari Its easy enough to hear. You don't have to take it on faith.

Hi Ralph: Do you any plans for a Class D preamp in the future?

Technically that is possible but we've no plans currently.

How one can know that it has "enough power"? Strange things happen. I have tried large Thiel speakers with a 200 watts class AB amp and i felt that, may be, the power was not enough since it sounded a bit "forced" at moderately high volumes (if this a correct way to judge if the power that an amp can give is enough for a speaker). But i don't observe similar things with a tube SET 5.5 watts amp connected to the same speakers.

Clearly the amp has enough power, unless its actually damaged in some way.  The 'forced' sound may simply be distortion though. Keep in mind that not all class D amps sound the same- I imagine some can indeed sound 'forced' and other amps simply don't.

This is a very strong and challenging statement, especially from a tube amplified producer (i appreciate it very much). I did believe in this a few years ago. Nevertheless, so far, as mentioned earlier in this thread, i did not find a class D amp that sounds as good as  my 5 watts tube SET class A amp. Perhaps, Orchard and Atmosphere  already produce such class D amplifiers... 

@orchardaudio and @atmasphere, do you expect to have a further breakthrough is the design of your class D amps in near future? 

I realized that i don't have an answer on the following (perhaps stupid, forgive me) question. Would it make a sense to combine somehow GaN transistors  with Purifi modules in a single amplifier? 

To the last question, no. The reason why gets really technical fast!

To the former question, I suspect any manufacturer in high end audio is looking for ways to improve their product, but I don't expect a 'breakthrough'; IMO/IME the breakthrough has already occurred- you can now finally buy a solid state amp that sounds better than the best tubes can offer (with the same liquidity, no harshness but with greater detail including depth), with the possible exception of the sound at overload (but for that just make sure you have enough power).

Atmasphere class d amps can also be interesting. I did not find them on the site and have no idea on preferences made in their design. Neither i know if there are already completed models. Can Ralph provide  more detail? 

I can. Its been the most successful product entry we've ever had. We started shipping last June. We didn't put up the product page until about 2 months ago. Early on the project (about 5 years ago) we had a prototype that demonstrated that the idea was worth pursuit- and that a class D amp need not have any audibly objectionable characteristics.

The simple fact is most output sections in traditional amps have distortion product based directly on their linearity. And since the output devices are not all that linear, feedback has to be applied to make them look better on paper. That's been a problem in solid state amplifier design since the inception of solid state. Class D does not deal with that problem, since the output section does not rely on linearity at all- it switches. So the distortion generated has entirely different sources!

One problem in traditional designs is getting enough gain and bandwidth to support the amount of feedback used. Traditionally this has meant that the feedback at 100Hz is quite a bit different from what it might be at 3KHz or 7KHz and as a result brightness and harshness has been present (put another way, if there isn't sufficient gain and bandwidth in the circuit, the feedback will decrease with increased frequency).

We've all heard this over the last 60 years of solid state amps; brightness and harshness is for many one of the worst failings of any audio system!

Class D offers a way around that, by allowing for profound amounts of feedback that is very difficult to do even with modern devices in AB circuits! With such high amounts of feedback its possible to build an amp that is both low in distortion while relaxed and detailed better than the best tube amps. To some this last statement might seem a bit weird but the experience of amps with low distortion not sounding all that good is common. At this point (and take this from someone who has been at this over 50 years) I'm very convinced that tube power amps are on borrowed time.

I play a set of our class D amps at home if that tells you anything.