High end Class D amps?

@atmasphere -nice explanation. Thanks.

@twoleftears - I actually think that 1KVA toriodal is undersized for a hi-end stereo Purifi amp. I've generally found that using a larger power supply improves the dynamics and authority in the mid-bass and results in a more pleasing sound. I don't know how much this translates to class D designs, but I would expect the same applies. 

The Purifi modules' over-current protection doesn't kick in until 25A, so it seems like there's value in using a beefier supply. The DIY Purifi amps I'm building will use a 1.5KVA transformer for each monoblock, although a small portion of this is allocated to the lower voltage supplies.

I am no EE, but Ralph's explanation is clear to me.
How another member cannot accept this is beyond me.
Bob

one more vote for PS Audio Stellar S300. I was a bit critical with that amp in the earlier thread ("Time to buy a class D amp?"). This was my first class D amp, and I switched from pure tube setting. More importantly, I used it with PS Audio Gain Cell pre/DAC, and none of the units, as it turned out, had enough burn-in time. Both units (Gain cell especially)  needed almost 400 hours to perform at their best. Now I think that the combination is quite good, not only S300 is a good amp, but Gain Cell is a decent preamplifier, especially relative to their prices. As part of my secondary audio system, I am quite pleased also with the pre. It has a characteristic that do no posses top level pres, it sounds good on old (relatively poor jazz) recordings, that I really like for my secondary system. Its DAC is not as good, it remained a bit harsh and rough,  I use an external DAC with it. 

Having auditioned a number of class D amplifiers since the earlier thread, my general opinion on class D has been changed. For me, it is clear that this is the future of the amplification, and there is not much one can objectively complain about them, in general. I like also tube amplifiers, just like I like some old car designs, but I think this is more a matter of teste, there is not much of objectivity there. 

You have much better price, less energy consumption, less weight, less hit, and better sound. Would you be willing to spend 10 times more to get something that is "apparently" a bit better only in some aspects and worse in the rest? 

As I keep saying.....everything makes a difference. There is no Class D sound. For instance.....every amp that uses the Purifi modules will sound different from each other. It is not just whether the power supply is linear or switching.....for a great switcher will beat a not so great linear. Every single thing has to be tweaked to the max. The input stages, the regulators, the wire, the connectors, the jacks, the fuses, all has a sound.

By the way, if you are using a toroidal transformer and you use metal plates or bolts to secure it to the chassis....you are closing down the sound. You want your toroidal transformer off the chassis on a piece of wood an mounted using tie wraps and glue or a wooden plate on top and teflon screws......way better sound.

Here is something really important: All Class D amps use a filter on the output to filter the around 500K switching frequency. Without this series coil and shunt capacitor your speaker would fry. It is common knowledge that you would never want your mids and highs in a speaker to go through a ferrite core coil. (Most speaker crossovers use coils, caps and resistors.......for coils the choice is either ferrite core or air core). No high end loudspeaker uses a ferrite core coil in the mids or highs......bass....yes.....everywhere else it degrades the sound noticeably.....

So, why is it that all class D amps use a ferrite core coil on the output of their amps? Why would you want to mess up the sound with a ferrite core coil? You won’t if you value sonics. However, class D was made to be small and efficient and an air coil coil would be too large, and too expensive and possibly radiate more rf.......so, they are never used.......except for NOW. On the mods I do to the Purifi module I change the stock ferrite core coil to a custom made 12 gauge OFC copper coil. This sounds way more open and real then the stock coil......this is a breakthrough. You see, every class d amp that any of you has ever listened to has a ferrite core coil on the output. By the way, only the best air core coil will beat the stock coil. You have to listen and test and listen and test. I also use better sounding caps to ground on the output of the coil and orient these caps so that their outside foil is towards ground, for best sound. I also bypass the output stage power supply with my modified Wima caps for faster and cleaner sound. These caps are also oriented for best sound.

No class D module is "pure" or has not sound. All are compromised. No class A amp is "pure" or has not sound. You start with the best circuit....and tweak it to the max. This is how you get great sound. Using regular integrated circuit op amps on the front end will not get you the best sound. I even modify the discrete circuits and regulators I use. This game in infinite. What is best today is tomorrows boat anchor. What I try to do is create products that are so good for the money......you can use them for years without finding a boat to mount it on.

I just now thought of this.  If you are building a Purifi class D amp and you want the mods I do to the output boards then I can do them for you.  I will have to figure out the price.  Call me if interested.

@ricevs - Thanks for the offer, but I think there is lots of low hanging fruit to focus on before attempting to modify the Purifi module. At some point, I might consider it.