Why aren't "power DACs" more prevalent?

[Purité Audio]

New Class-d design from Bruno,
https://www.monoandstereo.com/2019/02/new-lyngdorf-class-d-amplifier.html#more
Keith

 

[DonH56]

OP was asking about PWM throughout not Class D. The input to Class D amplifier is analog, isn't it? In fully digital converters, it is
PCM -> PWM -> low pass filter -> analog output. The only such DAC+amp combo in existence that I am aware of is Sony's S-Master. Apparently, TI and Philips have/had such devices in the past?

I was addressing the question about feedback in class D amplifiers asked by Theo in the post above mine.

 

[Blumlein 88]

New Class-d design from Bruno,
https://www.monoandstereo.com/2019/02/new-lyngdorf-class-d-amplifier.html#more
Keith

I wonder if that is basically like the current Mola Mola amps?

 

[Stonetown]

One problem which concerns me about D-amps, is that the damping factor is quite low at highest frequencies, but for bass frequencies no problem. When connected to speakers with varying loading impedance vs frequency (as with most speakers), the lower damping factor makes the frequency response not so flat any longer. Anyone seen a class D-amp with damping factor in the level of 100 (or output impedance of about 0,1 Ohms or less) at treble frequencies?
Cheers, /Per

 

[Blumlein 88]

One problem which concerns me about D-amps, is that the damping factor is quite low at highest frequencies, but for bass frequencies no problem. When connected to speakers with varying loading impedance vs frequency (as with most speakers), the lower damping factor makes the frequency response not so flat any longer. Anyone seen a class D-amp with damping factor in the level of 100 (or output impedance of about 0,1 Ohms or less) at treble frequencies?
Cheers, /Per

While they have rising output impedance I believe several are nevertheless rather low even at 20 khz. The Lyngdorf in the above link is less than half a milliohm at 20 khz and lower as frequency drops. Many of the Hypex designs from datasheets are a few milliohms at 20 khz. I think all of the Hypex are less an 100 milliohms at 20 khz.

You can download Hypex datasheets here with the output impedance listed at 1 khz and 20 khz.
https://www.hypex.nl/oem-audio-amplifiers/

Here JA tested an Hypex based Bel Canto and said the output impedance was a low .1 ohm 20hz-20khz.
https://www.stereophile.com/content/bel-canto-eone-ref600m-power-amplifier-measurements


The class D with rather high 20 khz output impedance are some of the ICEpower modules. I'm not sure if the latest versions fix that issue or not.

 

[HammerSandwich]

Example: NC400 datasheet claims <1 mΩ to 16kHz and no more than 2.5 mΩ to 20kHz.

 

[DonH56]

One problem which concerns me about D-amps, is that the damping factor is quite low at highest frequencies, but for bass frequencies no problem. When connected to speakers with varying loading impedance vs frequency (as with most speakers), the lower damping factor makes the frequency response not so flat any longer. Anyone seen a class D-amp with damping factor in the level of 100 (or output impedance of about 0,1 Ohms or less) at treble frequencies?
Cheers, /Per

The output impedance of any amplifier rises with frequency and is not all that great for class A/AB amps as well. They depend upon feedback to maintain those very low output impedances (or very high damping factors if you prefer) and loop gain decreases with frequency. The bigger problem for class D amplifiers is usually the phase shift from the output filter rather than any impact of higher HF output impedance IME/IMO.

 

[Stonetown]

The class D with rather high 20 khz output impedance are some of the ICEpower modules. I'm not sure if the latest versions fix that issue or not.

Yes it was in fact the ICEpower modules I was referring to. Thank you for the good news about those other brands. Also you HammerSandwich. Very nice figures! Thanks!
Cheers!
/Per

 

[Stonetown]

The bigger problem for class D amplifiers is usually the phase shift from the output filter rather than any impact of higher HF output impedance IME/IMO.

Yes I agree fully, about the output filters, but it appears have been solved now by the latest better amplifier makes. Very interesting and good news and if we get our hands on these modules, I think its hard to get any better. Maybe I will replace my Technics SE-M100 amplifier some day . Spec of it attached, and it appears that those latest Class D amps having as good specifications. Great!
Cheers!

 

[DonH56]

Yes I agree fully, about the output filters, but it appears have been solved now by the latest better amplifier makes. Very interesting and good news and if we get our hands on these modules, I think its hard to get any better. Maybe I will replace my Technics SE-M100 amplifier some day
Cheers!

Yes, see post #15 in this thread for a brief discussion. Basically a combination of higher switching frequencies made possible by newer technologies and better feedback/feedforward schemes (though I did not discuss alternative feedback circuits; figured I was already glazing too many eyes in that post).

 

[Theo]

I'll take a stab at it but more learned engineers may correct my discussion.

Thanks Don for this comprehensive explanation.

 

[NTomokawa]

OP was asking about PWM throughout not Class D. The input to Class D amplifier is analog, isn't it? In fully digital converters, it is
PCM -> PWM -> low pass filter -> analog output. The only such DAC+amp combo in existence that I am aware of is Sony's S-Master. Apparently, TI and Philips have/had such devices in the past?

Yea, that's what I meant by "full digital". I know that Class D has pretty much nothing to do with "power DACs".

 

[JohnBooty]

I believe Vanatoo's well-regarded powered speakers use amplification of this variety, with D2Audio ICs.

"Are there any other benefits to the Class D amplifier?​

​

Absolutely, since most of your music is already in digital format (e.g. CDs and downloaded music), if you connect your music source to a digital input on our amplifier (Coax, Optical or USB) your music will remain in the digital domain from your music source, through our digital signal processor (DSP), and on through the Class D amplifier final drivers after which it is converted to analog for the speaker drivers. The result is an audio path that has a minimum of conversions between the analog and digital domains..."​

​

https://vanatoo.com/audiospeak/class-d-amplifiers/

 

[HammerSandwich]

Putzeys describes the Purifi amp as an improved Ncore. Details here.