I don't see the potential dead times being similar as Qrr is a significant contributor of the dead time requirement outside of basic MOSFET switching performance.That's the body diode thing I mentioned.
Class D
Been thinking of trying a D amp to reduce clutter. Most that I see are not rated at 2 ohms. My PSB Stratus gold's will drop to 3 ohms or lower at some frequencies. So my question is will these types of amps handle this impedance ?
Thanks in advance. Chris
Thanks in advance. Chris
290 responses Add your response
Stop trying to divert that you were very anti GaN, and now pro just because it will be "the format" and suit your sales/profit modeling.Actually you’re hard pressed to find me being ’anti GaN’; that statement is false. What is true is that I did not believe that they could work without heatsinks and it was your heckling that caused me to take a look. Its true that for evaluation you don’t need heatsinks and most of our GaNFET prototypes didn’t use them. But in practice, ***they do in fact actually for real do need heatsinks*** which. again, was my original belief. Otherwise, you can expect them to blow right off the circuit board when subjected to low impedance loads at full power! Ask me how I know this :) The primary advantages of GaNFETs (compared to mosfets) are low on resistance and low input capacitance.The low input capacitance is a major deal! It makes the driver situation easier to manage. The lack of a body diode is the other issue. Between these two, that’s a good portion of why they are faster. These things interact with the choke in the output filter; GaNFETs won’t switch right if the filter isn’t there to give them a bit of an inductive kick to initiate the switch. Strange but true. We’re talking about something called ’inverse conduction’. Allowing for less deadtime is of course important. But since both GaNFETs and MOSFETs are operated far below their maximum switching capacities I don’t see this as the big advantage; you can run MOSFETs at the same speeds we’re seeing now with very similar deadtimes. After embarking on this project at this point I think Technics is missing a bet by switching so fast. Deadtime is a constant and does not change with the switching frequency; so the faster you switch, the greater the percentage of the supposed ON time is taken up with deadtime, which increases distortion. Put another way, if Technics simply reduced their switching speed they could get lower distortion. |
Saying they are not "faster" is only accurate if you take a very narrow view of "faster". When you look at equivalent RDSon/Vout, you would be hard pressed to find similar speed in silicon. Big advantage is Qrr is 0, but effectively that is tied to speed as well allowing less dead-time. Lowfi does not know this. |
The primary advantages of GaNFETs (compared to mosfets) are low on resistance and low input capacitance. The low on resistance allows for higher efficiency, particularly into lower impedance loads. In car audio, available power is pretty limited so it stands to reason that these devices would be making inroads here. |
Stop trying to divert that you were very anti GaN, and now pro just because it will be "the format" and suit your sales/profit modeling. One thing you "may" not have factored, is going to be the ones at less than 1/2 the cost of yours, and better advanced from those bigger companies.Now GaN is even making a "big noise" into car poweramps now also. |
And Ralph search is your friend, you might want to be reminded, that you were anti GaN fets way back at first, they are still the same ones buddy.You are quite correct. When you first commented that GaNFETs didn't need a heatsink in an evaluation circuit, I didn't believe you. But I followed the link you provided and promptly went down the rabbit hole learning more about it. So you can rightfully take credit for that. What is puzzling here is that even though you knew that bit about heatsinks, most of the rest of it is a complete unknown to you. For example, if I were to ask you, 'what is the **main** advantage of GaNFets?', what would be your answer? If you answered 'speed', you would be incorrect. GaNFets have lost their speed advantage over MOSFETs, which have continued to improve since GaNFETs were introduced. |
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ooooo strong come back :-) https://www.audiosciencereview.com/forum/index.php?attachments/purifi-1et400a-class-d-amplifier-modu... Salt in the wounds .... |
For one it was done at very low power, would be much worse at normal power There you go georgehifi, illustrating that YOU do not understand how electronics work and how Class-D amplifiers work. Signal level will have 0 effect on this. There is something that will though. And here is the distortion of a very good amplifier: https://www.audiosciencereview.com/forum/index.php?attachments/purifi-1et400a-class-d-amplifier-modu... Makes your "good linear amp" look like a 1970’s discount Realistic Receiver. And if you can't see that that 10KHz square wave is a quite good square wave, then you are even less "aware" of audio/signals than I thought. |
https://www.stereophile.com/images/1220PS1200fig03.jpg Really! Wake up and smell the roses!!! and stop your shilling! For one it was done at very low power, would be much worse at normal power Yet even at very low power anyone can see it’s distortion rising markedly from 1khz! up, and then much sharper after 2 to 3khz!!! to a cliff face at 5khz and up!! https://ibb.co/6rfG2ts Here is the distortion from a good linear amp. https://ibb.co/8rTdp3D |
georgehifi8,388 posts01-26-2021 10:25pmYou you don’t even understand what you asked, they utilized one graph instead of two just to confuse the likes of you George telling other people "they don't understand". That is ironic. |
I don't know, you would have to have some serious vision problems or some serious dogma problems to this this is an unrecognizable square wave ..... https://www.stereophile.com/images/1220PS1200fig03.jpg |
Having owned a EVS1200 for over a year now, and having made a few component and cable upgrades, most notable to date, I replaced my Emerald Physics KCIIs (with Wire World OCC wire and Clarity cap upgrades as new) with EP 3.4s (also
with Wire World OCC wire and Clarity cap upgrades) which I played without adding 2 SVS powered subs until about a month ago. I feel sorry for those who didn't jump on this amp, as he has stopped making them. Both Absolute Sound and Stereophile have glowingly reviewed the PS Audio M1200s (same IcePower modules, but stock). I am confident that the EVS 1200 would stand out against them for barely 1/3 the money hth |
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Once the switching noise is removed when very low power testing using the "Audio Precision’s auxiliary AUX-0025 passive low-pass filter, which eliminates noise above 200kHz that might otherwise overload the SYS2722’s input circuitry."You can get either a clean square 10khz square wave, but it's almost indistinguishable if you don't use the AUX-0025, because of the imbedded switching noise, because the amps output noise filter is set very high > 100khz Or you get a very slewed sick looking 10k square wave with phase shift, but with not much imbedded noise because the units output filter is really working hard down low <100khz. What ever you do, neither is right. The only right is as Technics did move the switching frequency up 3 x higher to 1.5mhz and then so also the switching noise filter, then it can do it’s job properly and not effect the audio band with phase shift from 20khz down. |
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The ICE 200AS2 has this same graph which shows a phase shift of almost 90° . I've never seen these types of plots presented this way and they don't do it for all their models. https://icepower.dk/products/amplifier-power-modules/as-series/ |
I should point out that any amplifier designer who knows his stuff of which you know who is not, could create an analog filter on the input that creates an inverse phase-function to compensate for the amplifier phase shift. This is essentially what Technics does with their GaN amps, but they do it in the digital domain. queue deflections and insults .... |
Well put djones51 The time coherence is w.r.t. blending drivers at the cross-over point, not across the whole output. If you ever looked at electrical phase versus acoustic phase you would see that what you describe is a rarity in speakers if at all. One simply needs to look at the impulse functions for that. However at the crossover point it is important so you don’t have peaks and valleys in the response. Turns out our ears/brain have never been shown to be that sensitive to phase, not surprising when you look at the physical structure, but I digress. It does appears that the phase shifts almost 70 degrees, but if you understand LC filters and output impedance, you would know this would not be possible as the L would make for a very high impedance, the C a low impedance and you would get a much faster drop in the response curve. To be honest, it is not completely clear whether they are looking at the phase of the output impedance or what. I know when you look at an amp that includes a "special" 1200AS you see a pretty clean square wave at 10KHz which would be impossible if the phase response was that variable over those frequencies. https://www.stereophile.com/content/ps-audio-stellar-m1200-monoblock-power-amplifier-measurements and the BelCanto which I think has an older 1000AS, has a very good 1KHz square wave indicative of little phase-shift from 1Khz to 10-20KHz. https://www.stereophile.com/content/bel-canto-ref1000m-monoblock-power-amplifier-measurements The 700AS has about 25 degrees at 20Khz, half that at 10KHz, so at cross-over frequencies fairly minimal. Just remember that people put super tweeters on top of their speakers and don’t align them to fractions of a mm .. but I digress. https://icepower.dk/support/#download-expand |
Common jonesy really!! The "ohm" is for the blue trace showing output impedance of the amp v frequency The red is just phase degrees v frequency On very good "phase correct" speaker/drivers that you paid big for!! and especially ESL, you would hear upper mids and highs that are 70 degrees (almost 25%) out of phase, compared to being in phase from below the upper-mids. Why do you think good manufacturers strive for "time coherent speaker design", even going to the lengths of staggering the drivers mounting distance to the listeners ears. |
This graph https://ibb.co/MS3xC6M I have seen on other forums but I never quite understood it. Is it showing that the impedance at 20Hz is .005 Ohms which stays fairly flat to 1Khz then rises to .05 Ohm at 20 Khz? The phase shifts 70° from .025 Ohm to .015 Ohms across the 20hz to 20 Khz? This is the electrical phase of the amp? If so did they adjust for time delay ? I don’t really understand all this but I don’t see how the electrical phase of 70° over a .10 Ohms is very relevant to how an amp deals with a speaker? |
+1 for "good" NO they are not a Pass Labs amp+1 on that too, and other amps I’ve mentioned as well I love them doing bass duty..Nice and cool running+1 here too, so long as the load isn’t too severe as they will current sag. Nice and cool running for the summer months doing mids and highs+1 again, but can’t yet compete with a good A or A/B amp yet, which run far hotter Time to feed the chickens..+1 except mines wombats/koalas Cheers George |
We’re talkin’ glue factory boys... this horse is dead.. Of course class D is good, NO they are not a Pass Labs amp or sound like one. They do sound pretty good though.. I love them doing bass duty..Nice and cool running..for the summer months doing mids and highs. Then back to valves for the spring winter and fall. BUT BASS all class Ds 12Ks, with a few exceptions.. Time to feed the chickens.. Regards.. |
George will never "prove" anything. He is full of conjecture, but not a thought out fact in site. Not one word or technical analysis of his own. Just tired stereophile links for data does not indicate that he thinks it means or he tries to use one example to imply all must be like that. Hey georgehifi, still waiting for you to tell us why all those amps you idolize have tons of feedback and it is okay. Still waiting for you to tell us why Technics must use digital filtering techniques to compensate for phase-shift in their amplifiers. |
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Tag team shilling that’s a new one for Audiogon. And Ralph search is your friend, you might want to be reminded, that you were anti GaN fets way back at first, they are still the same ones buddy. Your so full of it, all you have on your mind is to get your Class-D out there in the best possible (even if false) light that you can, anyone can see it. You would have been better just bringing it out quietly and hopefully resting on the laurels of your history on tube OTL’s. One more time for the masses, Class-D is not yet in the "very hi-end range" of amplifiers, like the Classics linear A A/B beasts that are still being made now, or even from yesteryear. Technics Class-D with the SE-R1 are the closest still to date. |
The other problem is current delivery into very low impedance speakers, like the classic linear high end amps can, that could take some more time, but they can drive the speakers that aren’t such a savage/nasty load like Wilson Alexia etc, so it’s not an overhaul big problem.George, you might want to know something about testing in the US. Back in the 1970s many companies were making some pretty outrageous claims of amplifier power. So the Federal Trade Commission (FTC) stepped in and made some rules. The first was that the output power of any amp sold in the US had to conform to something called ’RMS Power’ which has no meaning outside of the FTC rules, but is essentially the output power using RMS volts to calculate the power. The second was temperature pre-conditioning of the amplifier prior to testing it. This was done because in a traditional solid state amplifier if you run it at full power for a few minutes you’ll overheat it. So the pre-conditioning rule is where the amp is run at 1/3rd full power for one hour after which it is then tested at full power, which might only take a few seconds. This was simply to avoid damaging the amplifier during its testing. It might interest you to know that our prototypes, which are making 200 watts into 4 ohms, can run at full power on an indefinite basis! This is only because our circuit uses GaNFETs and a minimal heatsink design. You can hold the amp module in your hand while this is done and it does not get hot. I have to assume that is true of any module using GaNFETs although I’ve not checked that out. But this is **quite different** from traditional solid state amps which will blow up if you treat them like that! Additionally its worthy of note that distortion does not change as the module heats up, since bias of the output section is not affecting the distortion. Since our output devices have a rating of 35Amps, we can easily double power (400 watts) into 2 ohms no worries. We do reach a limit of doubling power into 1 ohm- the safety margin of 50% is exceeded into that impedance at full power (meaning that the module has a chance of surviving that but generally with any solid state design its good practice to not exceed 50% margins of maximum specs). Of course if the amplifier is not being pushed to full power then doubling its output will go on even if the load is less than 0.125 ohms! If we wanted to make more power into such low impedances that could be done with more output devices. Generally when such high powers are needed, the output circuit employs what is known as an ’H’ bridge. This allows the output devices to make more power without their voltage margins being exceeded. This however is true of any class D amp; the limits **are the same as seen in any traditional design**: 1) the current capacity of the output section 2) the heatsink capacity and 3) the current available in the power supply. IOW the statement I quoted from you above is outright false. This is very easy to determine. Again you don’t have to take my word for it; Google is your friend. Willful ignorance is stupidity; misinformation for its own sake is a heinous act. |
I think by now everyone knows why georgehifi does not address specific points made by atmasphere and I with logical, and numerical arguments of his own, using his own words. I think we know why he avoids addressing things like Technics using DSP to compensate for phase. It would be nice if he didn’t repeatedly in every Class-D thread have to tell us why. |
Yes, atmasphere, I come here for much the same reason, and georgenofi, is an almost constant stream of misinformation. Yes I sure do admire them in Class-D circles for advancing/sorting out (in the SE-R1) one of Class-D’s main problems, switching noise filtering which creates up to 70-degrees phase shift down into the audio frequencies https://ibb.co/MS3xC6M. Please all note, that georgehifi, I assume out of previous technical ignorance, but now I have no idea, refuses to accept the fact that Technics does not eliminate phase shift with only high frequency switching. They also apply digital filters to shift the phase at higher frequencies. They must do this because they do not have the technology to address it in a different way.
You mean like these amplifiers that you idolize? Gryphon, “big” Krells, or D’Augostino, maybe a JC1 pair The other problem is current delivery into very low impedance speakers, like the classic linear high end amps can, that could take some more time, but they can drive the speakers that aren’t such a savage/nasty load like Wilson Alexia etc, so it’s not an overhaul big problem. One of the better known Class-D amplifiers has an instantaneous current peak of 26 amps. For those better at math, that is 1350 watts, though that would require a suitable rail voltage. How long it can sustain that is a matter of power supply and thermals. Most Class-D amplifiers are designed for real world performance without added cost that will only be beneficial in a bench power test. You would be very hard pressed, if not impossible to find music where the average power is >1/4 max peak where average is a 50msec window which is exceptionally short. We are talking loud grunge, not what most of us would consider music. More realistic would be 1/10th where the max peak is compared to the maximum average over a sustainable period. So that 1350 watts peak would match up with 150W continuous on the bench. If you have an amp that can do 1000W continuous, and 1000W on peaks, on real music, it will have no benefit over 150W continuous, 1000W peak in real world usage. p.s. George, before you bring up 1 ohm, I will remind you that EPDR has no bearing on this discussion. Bringing it up only shows more lack of knowledge. |
Georgehifi idolizes Technics This answer is for others that are interested. Yes I sure do admire them in Class-D circles for advancing/sorting out (in the SE-R1) one of Class-D’s main problems, switching noise filtering which creates up to 70-degrees phase shift down into the audio frequencies https://ibb.co/MS3xC6M. Without like some do resorting to a band-aid fix of throwing heaps of "musicality destroying global negative feedback at the problem", pity they don’t want to, or maybe just don’t have the design skill to be able to what Technics did, and put it in the too hard bin??. The other problem is current delivery into very low impedance speakers, like the classic linear high end amps can, that could take some more time, but they can drive the speakers that aren’t such a savage/nasty load like Wilson Alexia etc, so it’s not an overhaul big problem. Cheers George |
So you calling Rubbish! instead of calmly trying to explain yourself, is not hostile.Correct. Its simply factual; I have in fact often calmly explained myself. I've often received complements for my patience in dealing with your insults and mis-information, but since I've never met you, its hard to take any of the slings and arrows personally so I've no reason to be angry. I do feel a need to correct misinformation where it occurs, as a rising tide raises all boats. Regarding feedback. George, do you realize that all the solid state amps of traditional design you've pointed to employ feedback? How do you explain that they are alright and a class D isn't? In common vernacular this is known as 'talking out of both sides of your mouth'. In legal terms its known as 'dirty hands'. 'Dirty Hands' is the legal idea that one cannot reserve for themselves a right that they do not also confer to others. At this point all the objections you've raised have been debunked, including the one about me being in 'product protection mode'. I think that you do not understand my motivations: right after high school, the very next day, I was employed by Allied Radio Shack as a service technician in their 5-state service facility. I enjoyed working there for years and used that income to put myself thru engineering school at the University of Minnesota MIT. In the late 1970s I started Atma-Sphere. As you know that involved tubes for a very long time, but I missed the troubleshooting I performed in the service industry. So I'm active on this and other sites, often answering questions that have nothing to do with my business. IOW I do it because I enjoy it. Now I can see that this is hard for some people to understand. But that's how it is. I do this because I enjoy it. Because of my experience as both technician and engineer (which can sometimes be at odds, technicians often find out about engineering errors before the designer does), I do feel a certain compulsion to correct misinformation. For reasons unknown to me (as I've no idea of your motivations) this means that you and I cross swords quite often. I see that as unfortunate. But from an ethical point of view I'm a bit between a rock and hard place when it comes to mis-information; if I sit back and say nothing, people will often flush perfectly good money down the loo. Its a bit like what happens when tyrannical forces come into power: Of course this is about education rather than power. FWIW though, willfully ignorant is almost indistinguishable from just plain stupid. |
Georgehifi whines about feedback in ClassD while idolizing solid state amps with tons of feedback. Georgehifi idolizes Technics while ignoring they need to use DSP and variable delay to compensate for phase shift in their output filter. Ignores circuit design requirements then faults performance. Just dogmatic rambling at this point. The hole is dug too deep to be willing to admit error. |
I have to say georgehifi according to you the only amps anyone should EVER own are Gryphon, “big” Krells, or D’Augostino, maybe a JC1 pair. It’s the same discussion, the same argument, the same bla, bla, bla. Sure you are a fan, those are some great designs, but get off it. They aren’t the end all be all, there are many, many excellent amps out there, a lot of which will drive just about anything. Given the lower sensitivity of speaker designs overall these days, premium designers do pretty well to design amps that do very well. Lots of opinion, not much substance here. |
And just because an amp uses tubes, doesn’t make it good. And just because an am is pure solid state doesn’t make it good. To me the purest form of amplification "so far" to date with least colourations, lowest distortions, unrestricted dynamics, unrestricted current ability even into very low impedances, and for hard to drive speakers Is high biased Class-A push pull direct coupled solid state amplifier, using complimentary bi-polar output devices with appropriate power supply/s and input/driver stage. Guess what some of them are? Gryphon, Classic/Krells, Dan/Agostino, some Mark Levinsons etc etc etc. Unfortunately, these are heavy, costly, and expensive to run. Many say Class-D is there, I say no not yet, unlike the few here will like to have you believe. And many others say also myself there are problems with it in the upper mids/highs. Also it definitely can’t compete with the above into hard low impedance loads of many of speakers, no matter how many watts they have. Cheers George |