High end Class D amps?

Hello arcticdeath,

     You're obviously inexperienced and have never listened to a good quality class D amp.  What makes you believe your opinion on this subject has any constructive value?

Tim

The idea that Class D amps are overly load sensitive was true with early implementations. We are way beyond that now. Take a look at this page about the PuriFi modules. With a 2-ohm load, the THD+N stays below 0.01% up to full rated power.

And to those who say, "The only good ones are made by XXXX." Really?  You've heard EVERY Class D amplifier out there, and under a wide variety of circumstances?

I'm liking my Bel Canto monoblocks. They have all the power and all the detail and none of the coloration and distortion. Works for me.

I have used them now with two different tube (valve) preamps. I've used them with my Acoustat speakers and it really brought them to life. I use them now with Goldenear Triton Ones, which can handle but do not need that much power (partly because they have class D amps built in for the low end) and that sounds great, too. Keep in mind that I upgraded from Adcom, if that helps.

Class D has clearly turned the corner in my opinion.

This is a smoke screen, they are still "basically" the same, with the same glaring problem, upper mid/highs phase shift, because of  the "switching frequency noise filter" on the speaker outputs.

The only REAL gains so far have been with GaN output devices, and the only one to utilize the 3 x higher switching frequency that they can operate at, is Technics with the SE-R1.
And because of it their "switching noise output filter" is 3 x higher also, therefore there is 3 x less switching noise present at the speaker output at 20khz,  and then also 3 x less "phase shift" going back down into the audible upper mid to high frequencies.

Until other Class-D manufactures have done this, they have clearly NOT turned any corners, but just taken small sideways manoeuvres to make buyers think they are being innovative.  

Cheers George

Class-D wattage instead of doubling for each halving of impedance load actually gets goes backwards when they see 2ohms and worse if there is any - phase angle involved, because they can’t deliver the current like a good bi-polar linear Class-a or a/b amp can.

This statement is false. The limitation of a class D amp is similar to what is is with any amp- how big are the heatsinks, how much current can the output devices handle, and how much current is available from the power supply.


The output impedance of any modern class D amp is only a few milliohms (the Purifi module' output impedance is lower than a foot of 18ga wire). So it can double power from 1 ohm to 0.5 ohms as long as the current doesn't exceed the limits of the output section. The real issue is the filter; lowering the load impedance lowers the effective 'Q' of the filter, IOW it flattens out the filter response. So as the load impedance is reduced, the 'residual' (which is the sine wave remnant of the switching frequency) will increase in amplitude. For any speaker this isn't a problem as the residual is very small on any competent class D amp.

One thing I find reprehensible is the way the big names have added all kinds of tweaks to Putzeys’ design (op-amps, power supplies) that are completely unnecessary, or even cause spec deterioration, so they can charge more. 

The reason everyone has different input circuits is because the module itself doesn't have one. Its input impedance is about 2,000 ohms- most preamps and sources would fall flat of their face driving a load like that. When you're designing a module, there is only so much gain you can get out of it, and you have to use an input circuit called a 'comparitor' which tends to have that low input impedance. So some sort of buffer is typically needed. You are correct that this can color the sound if not implemented correctly. Bruno of course has a recommended circuit, but its not cast in stone that it be used.