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The Truth about Modern Class D

All my amps right now are Class D. ICEpower in the living room, and NAD D 3020 in the bedroom.

I’ve had several audiophiles come to my home and not one has ever said "Oh, that sounds like Class D."

Having said this, if I could afford them AND had the room, I’d be tempted to switch for a pair of Ayre monoblocks or Conrad Johnson Premiere 12s and very little else.

I’m not religious about Class D. They sound great for me, low power, easy to hide, but if a lot of cash and the need to upgrade ever hits me, I could be persuaded.

The point: Good modern Class D amps just sound like really good amplifiers, with the usual speaker/source matching issues.

You don’t have to go that route, but it’s time we shrugged off the myths and descriptions of Class D that come right out of the 1980’s.
erik_squires
guidocorona
4,298 posts
 

Hello @d2girls, your question does not have an absolute answer.... A lot has to do with bersonal preferences, because Merrill, Rowland, and Bel Canto all make some wonderful devices.


Starting with Merrill... The Veritas monos were fabulous in their hayday.... Today they would still be worth a serios look... Although all things point to the new Merrill Oganessom series of Element 114, 116, and 118 being superior... Yep the Element 118 prototype that I had the fortune of having in my system for one week, while not well broken in and still evolving rapidly, was musically impressive to say the least!



Rowland has 5 class D amps.... two I know well and I adore... THe M925 monos that I own, and the Continuum S2 integrated.... The following I know by their excellent reputation only.... the Daemon integrated just below $39K, the M535 bridgeable just below $6K, and the little entry level M125 at some $2.5K.


Bel Canto has a number of amps.... THe Black series is their top of the line, while the Ref600 is more entry level.


All the above are great products, I doubt that you’d go wrong with any of them.... And I have not heard of any reliability complaints about their class D output circuits.... But which brand or model might be Best is pretty impossible to say.... It depends on your budget for one thing, but most of all on your sound concept.... Assume that none of them are strident, all of them are pretty linear, all of them let you hear subtle harmonics, all of them yield deep and tuneful bass without sloppiness.... And yet, inevitably you will develop a personal preference for a brand, or for a particular model, or.... You might dislike the whole lot instead *Grins!*


Why? ... "BECAUSE!"


G.

atmasphere's avatar
atmasphere
11,781 posts
 
By definition, zero deadtime means that the devices must be both on and off at the same time, a physical impossibility given any reasonable technology.
:) that is why we have a patent filed. Difficult takes a while- impossible is just a bit longer.

A Class D amp with Zero dead time is likely an amp with a short lifespan.
So far they run stone cold even when on for days on end.
erik_squires OP
16,039 posts
 
The problem is not dead time, or notch distortion. The problem is audibility and connecting that to any particular technical choice. 

What I mean is, all amplifiers, even all musical instruments, have "flaws." To some they may not be flaws, to some they may be "attributes." We can argue about them forever but the importance of any flaw has to do with it's audibility. 

We can talk about ways to mitigate "dead time" forever, but that does not make the issue audible. 

One thing that Revel and Bose both do incredibly well is to pay attention to technology not for it's own sake but for audibility and desirability. We could learn from these approaches. 

Best,

E
georgehifi's avatar
georgehifi
10,312 posts
 
The quote from Mr. Hammer is false. Here’s why:

As @merrilaudio states, the problem is dead time.
And the rest seems like an ad.


It’s not false as Ralph would have you believe.

It is "also" a problem, but isn’t the "major problem", and the cause is of what many dislike what they hear in the upper/mids and highs which is a product of the switching noise and it’s associated filter.

It is believed that the dead time will also be vastly improved with a 3mHz switching speeds.

This analogy from Nelson Pass will help:
"Imagine that the two transistors are runners in a relay race and that the signal is the baton they carry. In a real relay race, the runner receiving the baton begins running before the hand-off, which is made with the runners at speed. The runners who hand over the baton at a dead stop will operate at a severe disadvantage".

(if that runner can stop on a dime from full speed, then take off like a nitro drag car, you have higher switching speed)

And an interview with the great man (Nelson Pass) just a couple of months ago;

JS:There has been an explosion in high-end Class D amps in recent years. Some companies now market some fairly sophisticated – and expensive  – Class D models. Pass currently manufactures Class A and AB lines only. What are your thoughts on Class D?

NP: Personally I think it’s a miracle that they work at all, but then I think that about my phone, too. I have great respect for people who can make Class D amplifiers sound pretty good, and for delivering low cost, high power, and efficiency. They have earned their place in the industry.

That said, I am not tempted to go in that direction.




Cheers George
atmasphere's avatar
atmasphere
11,781 posts
 
The problem is not dead time, or notch distortion. The problem is audibility and connecting that to any particular technical choice.
Dead Time has nothing to do with notch distortion, but the chance exists that I mistook the gist of your comment.
It’s not false as Ralph would have you believe.

It is "also" a problem, but isn’t the "major problem", and the cause is of what many dislike what they hear in the upper/mids and highs which is a product of the switching noise and it’s associated filter.

It is believed that the dead time will also be vastly improved with a 3mHz switching speeds.
George, you've not thought this thru. You are correct that by increasing switching times you can decrease distortion. However, its not the filter that is an issue, in fact as the switching time goes up, there is a point where the inductance of the load is enough to eliminate the requirement for a filter!
(Usually the filter fails to remove all the high frequency component. This component is known as the 'residual' and if the filter is designed properly, will be a sine wave of low amplitude. As such it will not interfere with other equipment and is far too high to be heard!)
Now as you go higher with switching frequency, distortion goes down, but with any particular switching device- oh- I'm repeating myself; here's my comment that you apparently didn't read from above:
The problem is that dead time causes distortion. So with any given output device, there is always a certain minimum distortion and associated maximum switching speed.
Nelson's analogy is correct however, so imagine not having to wait for a transistor to shut off before the other one turns on! Now we can switch at much higher frequencies and with much less expensive parts. Alternatively, an amp with a lower switching frequency but no need for dead time can have distortion as low as an amp that needs the dead time and is switching considerably faster.


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