Anyone Recently Change to Class D power?

@milpai - Yes, my Purifi monoblocks each have a large linear power supply. You can see a couple of photos on my virtual system page. https://systems.audiogon.com/systems/8726

Each amp has a 1500VA transformer with about 200,000uF of capacitance. I’m currently using a Neurochrome input buffer, but I have a set of VTV tube input buffers with discrete Weiss op amps that I am going to try out as soon as I find a few hours to install them. I have to rewire some connectors, and I have another project I’m trying to wrap up first.

I wouldn’t say that these amps are necessarily better than the JC5. I could be content with either. The JC5 is a very nice amp, particularly for its price point. But the Purifi monoblocks have some non-audio benefits which tip the scale. The somewhat smaller monoblocks are a lot easier to tuck in near the speakers and don’t require large speaker cables going between the speakers. I have a set of french doors centered on the front wall that I want to be able to get to. Also, the Purifis run very cool and waste a lot less power when left on 24/7.

My speakers are fairly efficient at >92db/w and I don’t listen super loud, so both amps have more than enough power. I don’t really need to extra power that the JC5 offers. I have separate powered servo subs that handle below about 70 Hz, so I am really only comparing mid-bass and up.

The Purifi amps have a bit more slam in the bass and a wider sound stage (maybe because of the monoblock construction), and are a little more detailed in the mids/highs with a slightly more forward presentation (my preference).

The JC5s are a bit smoother in the mids/highs which helps hide some recording imperfections, and is a touch warmer sounding.

The differences in these amps is pretty subtle. I had to go back and forth and note specific things in the recordings in order to tell them apart. But my hearing isn’t as discriminating as it used to be. However, I found it pretty easy to tell the differences between these two amps and other DIY amps I’ve built. The Purifi amps are my first DIY amps that have made me seriously think about selling my JC5. I haven’t listed it yet, but have pretty much decided that’s what I’m going to do.

https://sklep.toroidy.pl/en_US/index
Is it silent?  Any hum?

Zero hum - neither mechanical nor audio. Mechanical hum usually comes from DC offset on the AC mains, or a transformer that is under spec'ed for the current demands.  

@jaytor ,Thanks for posting the details. Yes, I did check out the amp on your system page. You have a fantastic room. Amazing that the Purifi competes with the JC5. I would think the JC5 is a detail monster, knowing what the A21 can do. For me the JC5 would be the logical upgrade. But I am reading a lot of positive reviews on the Purifi modules. Only 1 joker keeps complaining that they don't double the power when going down for 8->4->2 ohms. I don't know if that is even needed, The JC5 does not do that.
Do you think that the Purifi can comfortable drive a speaker that dips to 2 ohms? Hence let me ask another stupid question - why use linear power supply instead of the switching power supply?I have seen your other creations. I don't know how you do it - but to me those components looks professional grade. Especially that Purifi amp. Keep it up!

@milpai - thanks for the kind words. 

Most class D amps are built with a switch mode power supply because they are a lot cheaper, lighter and smaller, so the overall amp can be a lot less expensive for a given power output. Modern class D amps have lots of negative feedback, so the power supply rejection ratio is quite high and with the simple distortion measurements that are typically used, they measure just fine. But that doesn't mean they are going to sound as good. 

Over the years (45 yrs as an audio enthusiast) I have found that a good power supply with plenty of current reserves has more impact on the sound quality than perhaps anything else in an audio circuit. 

A large linear power supply can provide much more current reserves and not introduce lots of high frequency noise that has to be filtered out or removed using feedback. I have not A/B compared a SMPS supply against a large linear supply with the Purifi module, but almost all high-end amps, including class D amps, use a linear supply.

On top of all that, I wanted to add my personal touch to the amps, and I'm a lot more comfortable building a linear supply than trying my hand at an SMPS. I didn't want to just drop a pre-assembled module in the box. 

And I'm quite happy with the way it sounds. I'm not sure how much of that was from the linear supply, but I don't think it can hurt (except the wallet). 

Regarding driving a 2 ohm load, class D amps have exceptionally low output impedance, and can easily handle a low impedance load. The only limitation is the maximum current. The lower the load impedance, the lower the efficiency the amp will operate, so at some point the amp will protect itself and prevent thermal overload (generally controlled by maximum current). The Purifi module is rated at 25A peaks which is more than enough to hit 800w or more into 2ohms (which is where the amp will voltage clip). It can't sustain this for long due to thermal limitations, but you don't need that unless you have very inefficient speakers. 

So it really depends on how much power is required by your speakers. My speakers are nominally 92db/w efficiency and I have to crank the heck out of them to come anywhere near clipping. I have a peak reading LED power meter on my amps with 32 segments measuring 1db increments. With all 32 segments lit, the amp is close to clipping (50v pk-pk). Most of the time I'm listening, I am barely blipping the second LED (approximately 0.3w).