Class D is just Dandy!
+1 kdude66 This equates to an output impedance of 1.25 Ohms at 20kHz and SIGNIFICANT phase shift within the audio band. Just what I’ve been saying all along, would be great if you can post a link to this. This is why it important to increase the switching frequency by hopefully x5, which then takes the filter up higher by the same amount, away from the audio band. And why the above transistor development (in my last post) is so needed to get it up there. Cheers George |
A little confirmation bias there, George. The phase shift in the nCore, if ONLY due to the output coil is minor, about 10 degrees, and almost none from 10kHz or below. We don’t actually know the output phase shift without a direct measurement. We can only estimate what a 10 uH coil would do. The size of the output coil is in the same order of magnitude of most SS amplifier output coils. Maybe 2-3 times bigger. Also please note the effective nCore 400 output impedance is not 1.25 Ohms at 20 kHz but around 0.003 Ohms. Probably due to feedback being outside the coil. These are minor quibbles. In fact, the interesting part about the Technics amplifier is that it solves this not by a better output section but by measuring the frequency and phase differences with the actual speaker load and then compensating for it at the input. This is pure frequency and phase equalization. You could do this with any current Class D amp plus a miniDSP if you chose to. The ICEpower amps on the other hand have much bigger phase shifts. No idea what it’s attributed to. Of course, time marches on, and progress will be made but what we have now is really very very good. Best, E |
It would seem many here hold their own share of beliefs and agendas either in favor of or against Class-D for a variety of reasons - certainly predictable and all too common to have some sort of investment in a particular design principle, sometimes based more in theorizing than drawn from actual listening sessions. Perhaps in an effort to counterbalance my own inexperience and skepticism, or even prejudice against Class-D designs in regards to successful implementation with very high efficiency loudspeakers (+100dB’s), does anyone here have practical experience in this regard and how this combo plays out? Typical "wisdom" seems to have it that Class-D designs are less favorable within the first watt of usage compared to Class-A designs - not least SET’s/SIT’s - and are therefore considered the poorer match with very high efficiency speakers. Is there any merit to this in the eyes (ears) among those with actual experience here, or is it a field laden predominantly with theory as to how things ’should’ (as opposed to how that actually ’do’) pan out? |
Hi Phusis, Not sure why high efficiency would be a bad combo. The issue with different Class D designs, as covered, has more to do (in my mind) with impedance drops of exotics. They are dead quiet. When I first heard digital amplifiers it was with a pro monitors based on pioneer metal-dome compression drivers. OMG that was painful. :) But that was in the 80's. Class D amps are also dead quiet, so that's not a big deal. Still, I don't have recent experience, so I hope some one who does will chime in. Best, E |
