Class D amps that are superior to all or most?
carlsbad Coincidentally I just got MLs and my tinnitus is quite a bit louder than normal. I've wondered if it was the brighter highs. but it is probably just that I'm listening to it more. I don't listen very loud, in brighter speakers I listen quieter. I'd say you haven't really heard what those ESL's can achieve in the upper mids/highs, until they are driven with a good linear high bias class-A/B amp. Cheers George |
@ieales If you look at my post that you quoted and the information you quoted next to it above, you'll see that we are saying exactly the same thing. TI's information cannot be construed to be seen as a change in frequency response. In that post you see me saying this: Its true that the output filter is affected by the load.To which you responded: Methinks not.If you look at these two statements they are quite similar!After that you followed with: The variations can be small, but they will vary with every load presented. Hence, the perceived sound of the amplifier can vary with each speaker.Its this conclusion that isn't quite correct. It can be true if the class D amp is using no feedback or insufficient feedback. If it has over 35dB, what happens is the feedback is so profound that it allows the amp to correct for minor changes caused by the Q of the filter with respect to the load impedance. The result is that the change to the audio passband bandwidth and phase shift is not measurable; i.e. there is no change. |
@atmasphere Your post began stating I have a misconception. I have no misconception of Class D, filters or Q. There is little change for some products as I showed. For others there is a lot. Designers debate the value of under, critical [for design load impedance ONLY] and over damping. Hence the wide FR variation among competing Class D products. Class D products VARY MORE into varying load impedances than do typical transformerless solid state amplifiers. Hence my caveat that fan-boy recommendations are just so much twaddle. Feel free to post unfiltered frequency response graphs of a Class D amplifier that maintains identical flat output amplitude into several 'rollercoaster real world impedances'. I've yet to see one. NOTE: I only mention FR as it is relatively obvious and most comprehend it. Not so much for IM, THD and dynamic distortion spectra. |
There is little change for some products as I showed. For others there is a lot.It appears to me to come down to this. The reason is the filter isn't the only variable- class D amps vary quite a lot; some have zero feedback, others have feedback and don't include the filter in the loop, others have feedback and do include the filter, still others are self oscillating and those that do might have the most feedback. The amount of feedback is the key. Less than 35dB in any amp simply won't work. We've measured no change in bandwidth of our prototypes and Beta units from 20Hz to 20KHz, with less than 1 degree of phase shift over that range, with the load from 2 ohms to 16 ohms. No change. So depending on the amp we are both correct. I think what is bothering me here is you do not draw a distinction with how the amp is designed and that makes quite a bit of difference to the outcome! Here is an example of what I'm talking about:https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-purifi-1et400a...:) FWIW the guy doing the measurements here isn't what I would call a 'fan-boy' :) |
We've measured no change in bandwidth of our prototypes and Beta units from 20Hz to 20KHzI don't think I ever mentioned bandwidth. BW is not FR. BW is how far. FR is variation over BW. Some amplifiers drive test loads ruler flat and reactive loads not so well. fan-boy: "I have a GigantaRama driving BrontoSpheres and it's great." Frequently, not. |
