Class D amps seem poised to take over. Then what?

So, it seems you have heard Bakoon. How would you describe them? Current drive?
Speaking of tintinabulation, I get that fully with AGD.

I was referring to the post above mine rather than the amp. Not many people use 'tintinabulation' these days :)  but its a useful word for things having to do with audio.

However what is missing is the decay,the harmonics, the shimmer,the lilt,the atmosphere,the musical feel,the tintinabulation.

Lovely. This property is not the perview of any particular technology IME.

You can certainly get plenty of body and warmth out of SS amps.It may not be typical for the breed but SS amps like that are not hard to find.Most of the Nelson Pass amps,Audio Flight,Electrocompaniet,Usher,Sugden,Dartzeel and
 many more.And Bakoons which are really special and seem to combine the very best traits of SETs and class A SS.

This is a matter of scale and I've not heard a conventional solid state amp including those on this list (excluding the Bakoon) that is as smooth and detailed as a good class D.

Can I simply inquire as to whether the new age of Class D amps are fostering that feeling of warmth and body that one gets from Tube or Solid State amps?

@briggtrim If the class D amp is designed properly, yes, it will sound smooth with warmth and body like a tube amp, something a conventional solid state amp (IME) cannot do.

Any suggestions of Class D that have decent image depth and musical engagement?

IMO the problem with Bruno's modules is that he makes them available for anyone to cook up the input circuit. Many designers have with really variable results! Almost any class D module is going to need some sort of gain and impedance matching at its input since the typical comparitor input (and all class D circuits have a comparitor) is often only about 2KOhms; far too low for most preamps and needing some level at the same time.

So that's one variable. You hope that whomever designed the input circuit knows what they are doing.

The other issue IME/IMO is the power supply. Unless you have an enormous manufacturing budget and can spring for a custom designed switching power supply, if you have a switching power supply its likely to have current limiting issues which can shoot down the amplifier design. For this reason I recommend looking for class D amps that have a lower tech power supply using a conventional power transformer and rectifiers.

So a Hypex can sound great if these issues are properly attended. That is why you hear such variable reports about Bruno's modules (UCD, Hypex and Purifi).

You've probably been hearing about the AGD Audion- all the reports I've heard about this amp indicate that its excellent (not heard it myself).

The other problem I am hearing is how mechanical it sounds.I hooked up my Gale 401s which are famous for their rhythm, groove and timing and now they sound like the music is being played by robots! I would have never thought any amp could do that but somehow it is.To me that indicates some fundamentals are really srewed up.

They probably are! But I think you also know that convention solid state amps can have problems as well as tube amps. Class D is no different in that regard- they can sound quite different depending on the design. We have a class D amp here in the shop that sounds for lack of a better expression, dead. But I have a pair of class D amps at home that sound very musical and lively. So If I were you, I'd continue auditioning amps (if you are otherwise interested in this technology) until you find something that ticks all the boxes.

Still not convinced sorry.I recently got to hear the latest Purifi class D [P452 I believe] in a very good system-Magicos/Accuphase and they still sound phasey.There is certainly less haze than earlier but they still struggle to create convincing image depth and height.So just not 3D enough.And sorry but the whole point of stereo recording and reproduction is imaging.I know a lot of people can’t seem to hear that sort of imaging and for them class D might be fine but it in absolute terms it is still flawed.

@jtgofish I'm not doubting your experience but to my understanding the Purifi module is not sold as an assembled amp- you have to buy them and assemble them into an amplifier. So a lot depends on how competent the individual was that did that.


I've not heard the Purifi, but I have heard class D amps that have as much soundstage width, depth and height that I've only heard in the best tube amplifiers (which easily best most of the solid state I've heard).


IMO if you really want to know about this you might try a different amp- one amp does not represent all of them.

My point was: people like the sound the way they like it. Class type, distortion signature, or whatever really doesn’t make a difference if someone likes the sound they have.

Yes. However its not as much a 'taste' thing as so many people think. This is because all human's ears obey the same rules and in the case of distortion this is critical to getting the amp to 'sound right'.

 What flavor or class is soothing to the taste buds or ears?

Its not the class of operation- its the distortion signature. If you've got that right the class of operation is irrelevant.

Just look at their independently measured 2ohm wattage figures (if you can find them) then compare to their 4ohm wattage figure, and see if the 2ohm even tries to come close to doubling the 4 ohm wattage figure, and post it up **** **** and if you don’t you full ** ****

“Youth ages, immaturity is outgrown, ignorance can be educated, and drunkenness sobered, but stupid lasts forever.” -Aristophances

If he believes this that’s fine - nice for him if it makes him happy.  I believe these perceptions to be (almost) completely subjective though.  

Not necessarily! It will sound like a tube amp if it has the same distortion signature and if you look at AGD's webpage for the product you'll see he published that. Not unlike an SET distortion signature... This is the sort of thing that's easily measured and heard.

Ahhh..Please reserve the term " Beta production" for software/mainstream tech ..NOT for the art of domestic audio....please

:)  Pretty funny

I liked the sound but I'm a ham radio operator and it generated RFI 

I had a class D amp in a subwoofer that interfered with FM reception! I got rid of it for the same reason. They're not supposed to do that and a properly built class D won't.

@timlub 

You never know, maybe Ralph @atmasphere  will design a switching tube amplifier. Ha

We've already done that- been working on it for the last 4 years. We're in Beta production right now.

If you think class d is better than class a or class a b you better get your ears checked LOL they've gotten a lot better but they're still not as good.

Instead of checking your ears, it might be more fruitful to check a different class D amp and see if you still say that. Class D, like tube amps or traditional A or A/B amps, are all over the map in terms of sound. Some manufacturers have sorted out what works and care about it, and others have not or don't care- same as its always been...

These companies that claim double wattage when impedence is halved don't give the actual 8ohm measurement, which is usually a lot higher wattage than their spec sheet has listed.

Our class D amps do 100 watts into 8 ohms and 200 into four. There is probably a slight difference due to the output impedance that causes the 200 watt reading to be inaccurate but its too low to resolve. But in reality the amp doesn't clip at 100 watts- it does so at 125 into 8 ohms but into 4 ohms it clips at 250 watts. So while your comment is true in some cases its not true in all cases.

You keep mentioning Wilson’s as being hard to drive, where does this come from?

For someone who "says" they’ve owned Wilsons, you are not very au fait or even interested in how they measure or behave, in particular the loading they present for amps to see.

While its true that the Wilsons have a low impedance in the bass (the Sophia and Sashas being the ones of their more recent lineup with which I'm most familiar) they really are reasonably efficient. When our MA-1 was hooked up to the Sashas (a friend of mine in town had them) the meters on the amp barely moved but there was plenty of volume. You have to take the drivability into account as well as the impedance. Our class D amps regard the Wilsons as a benign load.

Next you’ll say an OTL of Ralphs can drive those Wilsons to their best properly, because they too will stay stable into them and not oscillate.🤷‍♂️

The sales manager of Wilson had our amps for many years. FWIW our OTLs are inherently stable and will not oscillate with any load or input signal condition. 

they are fets, and fets can’t do doubling of 8 to 4 to 2ohms (current) like complimentary bi-polars (bjt) can do like in the the Gryphon Antillion, bigger Krell, D’Agostino Boulder, etc etc etc

This one gave me a good chuckle- its so ridiculously false as to be funny! This statement ignores a simple fact about GaNFETs which is their ON resistance is one of the lowest values of any semiconductor.

One reason I bought AGD is because I was convinced that they stood apart from all other Class D.
That all the others used variations of existing technology (chips).

It certainly helps when designing a switching amplifier to have also participated in related patents to switching transistors as Alberto has! But if you want to know why his amplifier sounds right, take a look at the distortion signature he shows on his website. If you look at the values you'll see that its not particularly low, but what is important (and IME arguably more important that *how much* distortion you have) is that the signature is what you want to see to prevent the amp sounding harsh. Here's the link
https://agdproduction.com/audion/
scroll down and click on either of the THD images. You'll see that the 2nd and 3rd harmonics predominate. These harmonics are nearly inaudible to the human ear and because they are so prominent, they mask the higher orders (which otherwise are audible usually as harshness and brightness). This distortion signature looks very similar to that of our OTLs (although we show more 3rd and less 2nd due to our differential design). This type of distortion signature will cause **any** amplifier to sound smooth and organic. The lower the distortion the more detailed the amp will be without also being bright.


I've said many times that the differences we hear in amplifiers has more to do with what distortion we can hear and what distortion that we can't. This is more important than output impedance because the ear has a tipping point where tonality generated by distortion gets more attention than actual frequency response.


Class D amps can have a signature like this because the errors (non-linearities) in the encoding scheme and the dead time requirements (if handled correctly) tend to result in lower ordered harmonic production. (There is more to it than that of course...) In a nutshell this will cause them to sound like a state of the art tube amplifier that acts as a virtually perfect voltage source.


If you are pragmatic as a designer you know that you can't make an amp with no distortion :)  The savvy designer will thus see to it that the distortion that is present is innocuous and this is a good example of how that is done.

...yes, but is Class D stable into 2 ohms?

Yes, depending what most meanings of the word 'stable' are. Yes, a class D will not go into oscillation when presented with a 2 ohm load (instability can result in oscillation- so that's one meaning of the word...). Yes, a class D amp can easily double power into 2 ohms or even 1 ohm, since its actual output impedance is probably only a few milliohms (our Beta production amps have an output impedance of about 10 milliohms).


With an output impedance like that, of course an amp can double power. But we also have to be clear about what limitations exist. The limitations are the ability of the heatsinks to get rid of the additional heat, the current available in the power supply and the ability of the output devices to handle that much current. So most class D amps might be able to double power into 2 ohms, but maybe not at full power.


One limitation with GaNFETs is the heatsink- because their appearance has a lot in common with a postage stamp, there's not a lot of methods available to couple them efficiently to a heatsink. And that heatsink has to be very effective at moving heat away from the device. This is (IME) the biggest limitation of GaNFETs; on the case of our design, the heatsink simply isn't fast enough to move all the heat away from the devices if operating at 2 ohms to full power (which would be 800 watts). The output devices are rated for the current, no worries there and its no problem putting in a power transformer that has enough current.


But are they stable? Certainly! For that matter so are any of our tube OTL amplifiers (in that they too will not oscillate when presented with an adverse load) although they certainly won't double power. So what this question really points to is the ability of the amplifier to behave as a voltage source (able to put out the same voltage regardless of load) and so long as you don't ask it to make full power into the load, almost any class D will do that like a walk in the park.


But at the same time its important to know that  **ANY** amplifier driving a low impedance like that will not really be able to strut its stuff. All amplifiers make higher distortion when driving lower impedances; from a high end audio point of view where its all about getting closer to the music, this is the Thing You Don't Do if you want your stereo to sound like real music- the additional distortion will manifest as harshness and brightness with a loss of detail.