Class D

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:

First they came for the socialists, and I did not speak out—
     Because I was not a socialist.

Then they came for the trade unionists, and I did not speak out—
     Because I was not a trade unionist.

Then they came for the Jews, and I did not speak out—
     Because I was not a Jew.

Then they came for me—and there was no one left to speak for me.

Of course this is about education rather than power. FWIW though, willfully ignorant is almost indistinguishable from just plain stupid.

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

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.

Without like some do resorting to a band-aid fix of throwing heaps of "musicality destroying global negative feedback at the problem",

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.

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.

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.