GaN amplifier from GaN themselves limited supply!!!

None of my posts have been removed.


The fact that these have sold out is probably not due to popularity in the high end audio community so much as GaNFETs are hard to get right now and there probably isn't stock to build the evaluation boards. When you can't get the product to sell, why in the world would you populate a promotional product??


I noticed George repeating himself in his quotes from Amirm but oddly he leaves out Amirm's concluding remarks so here they are from Amirm's website:

Conclusions
MOSFET transistors have revolutionized computing and switching power designs. It is nice to see a new type become available after decades of refinement of MOSFET. GaN transistors offered by GaN systems show a path to cooler running, more efficient and better performing amplifiers and power supplies. The eval unit unfortunately doesn't show the improved performance due to different target for it. So best to look at commercial implementations that shoot for state of the art implementations.

Note the last two statements.
Although George was rankled by this he didn't let on here on this website. He asked Amirm only a few days ago (most of the thread is from June) about changing the feedback to get better measurements- here's what he asked (on page 7 of the review) https://www.audiosciencereview.com/forum/index.php?threads/gan-systems-amplifier-eval-board-measurem...

Any chance of doing the couple of measurements again that didn't impress like the others did, but with the feedback set up higher where you think it should be, as this may well flip your conclusion around??.

Obviously George is aware of Amirm's conclusion.


Amirim indicates that he is concerned the evaluation board will go into oscillation if too much feedback is applied (for those technically minded: with too much feedback the phase margin of the circuit would be exceeded, resulting in oscillation). This is a clue into the design of the circuit. It indicates that its not self-oscillating. Since it can also be run with zero feedback (see measurements on page 1 of the review) this suggests a straight forward Pulse Width Modulated encoding scheme.


A PWM encoding scheme with no feedback has noise associated with frequency drift in the triangle wave oscillator. For this reason the oscillator has to have a lot of attention paid to its stability, but the simple fact is it will drift. You can see the result in the noise spectrum which is the final measurement Amirm shows.


One more thing: If you note the 4 ohm power measurement as opposed to the 8 ohm power you see that its actually **lower** (114 watts) than the 8 ohm power!


This is not a mistake.

I've already said why earlier on this thread- because the eval board is for evaluation only its not supplied with heatsinking means. Heatsinks that can actually allow the amp to run at full power into 4 ohms are not a trivial cost- they would be the most expensive part(s) in the kit due to the precision machining required. So the amp is teamed with a SMPS unit that is unable to provide the current needed into 4 ohms (and is probably actively current limiting). This prevents the board from overheating its output devices. 


So if you are planning this amp as your power amplifier, just be aware that its really only 114 watts into 4 ohms.

This says it all, the two that are trying their hardest to discredit this GaN by GaN Class-D have only their own interests in mind, and should look after their own interest and stop putting rubbish on things for their own monitory gains.

Whose trying to discredit it? You can't find any of my comments attempting to do that. You can find a number of them that are corrections of misinformation though.

This says it all, the two that are trying their hardest to discredit this GaN by GaN Class-D have only their own interests in mind, and should look after their own interest and stop putting rubbish on things for their own monitory gains.

Who is trying to discredit this amp? Its not me; you can't find a post on this thread wherein I am doing that. I have pointed out that its likely to have heat issues, but that does not take anything away from a product meant for evaluation.
Again:

It would help if more information was available. One thing seems apparent: While it might make 200 watts into 8 ohms it will not be able to do that for any length of time as there appears to be no provision for a heatsink (although it may be possible to heatsink it). Without a heatsink at 200 watts the output devices will simply overheat and fail- probably within a few seconds but maybe a minute or two.


IOW this kit really is for evaluation and for that I'm sure its just fine.

Note Amirm's comment 'different target for it'; clearly he is aware and understands the significance of this product being meant for evaluation):

The eval unit unfortunately doesn’t show the improved performance due to different target for it. So best to look at commercial implementations that shoot for state of the art implementations.

He seems to agree with me on this.

Yeah, just throw more bandaid fix feedback at it. (just like the zero auto former you push for the OTL’s into hard loads)

Everyone know too much feedback is detrimental to the sound, that’s why that GaN by GaN Class-D measured by Amirm had "very little feedback on it" programed from the owner, for the sake good sound, but of not measuring too well in certain parameters. (get with the program) and you and your mate stop putting     on everything that’s in opposition to what you’ve got coming, not just on this thread I’ve seen but others too!

And btw you can’t cure this kind of -75 degrees! of phase shift (red) with     loads of feedback https://ibb.co/S06J7hf only a 4 x higher switching frequency will move that up out of the audio band!!!

It seems there is doubt in your mind that George designed the Lightspeed and in my mind I just assumed he did because I have no evidence to the contrary and to my knowledge no one else has stood up and taken credit for it. The optocouplers which are the main component are off the shelf. The key is that they need to be well matched which I understand takes some work, but perhaps not necessarily skill.

@clio09 I included George's quote above because its typical of his false statements regarding the topic he's addressing: the **entire thing** is false. This sort of thing has convinced me that he's good at marketing but someone else actually designed the Lightspeed or provided the basic fundamentals. Here's a DIY article on the topic:https://diyaudioprojects.com/Solid/DIY-Lightspeed-Passive-Attenuator/The circuit simplicity belies what you go through to build it as you can see. If George were able to show that he can disabuse himself of false notions when presented with fact I'd be more likely to believe he did the fundamental design work on he volume control.

Also the switching frequency still has to be 4 x higher so it’s filter remnants and phase shift are "well out of the audio band" as Technics did with their GaN SE-R1 and maybe their SR-1000 integrated has also.

This statement is false. If there is sufficient feedback, phase shift at 20KHz will be under 1 degree even if the filter is set at 70KHz.


Also, class D amps if designed as self-oscillating (ex.: Hypex) are inherently stable regardless of load as they are **already** oscillating due to the amount of feedback they employ. You can't somehow get them to oscillate again over the existing oscillation....

As for heat there’s virtually none.

" Again, no heatsink due to high efficiency.s for heat sinking it runs so cool there’s no need for it. Practical MOSFETs take time to switch and during that time, they generate losses in the form of heat and limit how fast you can switch them. GaN transistors aim to solve this problem as these few slides from GaN systems show:"

This statement is false as anyone who has actually worked with GaNFETs knows. Sure, you can make an amp that does not use heatsinks (we didn't add any until we got very close to production) but the simple fact is that GaNFETs do produce heat and if you can't get rid of it, they will fail and often quite dramatically when they do. And you might think that you don't have to worry about shoot thru current heating up the output devices since they switch so fast, but you'll find out differently if you don't include deadtime circuitry to prevent that. But if you're just doing demo and don't run the amp at full output you can get by without heatsinks.

We expect people to abuse our products. So we built the amp so it can be at full output into 4 ohms and it can sit that way all day. That would not be possible without heatsinks!
But for evaluation I'm sure this circuit board is fine. You don't need heatsinks for evaluation applications!

Distortion at high power for a Class-D is incredible

"We see that the distortion is still under control instead of shooting through the roof.!!"

"I don’t think I have ever tested a switching amplifier with this level of frequency independence. Even Class AB linear amps struggle to produce such an absolutely clean response. Amplifiers with high amount of feedback run out of gain at higher frequencies and hence distort more. Not this design."

This has nothing to do with GaNFETs and everything to do with the design. What is being referred to here is sufficient Gain Bandwidth Product, which most amplifiers lack in order to have feedback and consistent distortion numbers at any frequency in the audio spectrum (this BTW is a requirement if the amplifier is expected to sound musical). I've made comments about this aspect elsewhere on this site. What this says is that Amir hasn't tested a lot of class D amps; Bruno Putzeys' designs share this property of consistent distortion at all frequencies, and his designs use MOSFETs.

I know sometimes it's difficult to look past the person based on their comments and interactions with others, but George designed and built the Lightspeed Attenuator which I've owned for over 10 years and consider one of the best values in audio.

@clio09  I agree the Lightspeed is one of the better examples of a passive volume control. To make the devices inside do what they do (which is to say, operate in a linear fashion) takes design skill. Why do you think George designed it- doesn't that seem a bit odd?

Ummm someone’s not impressed.😴

It would help if more information was available. One thing seems apparent: While it might make 200 watts into 8 ohms it will not be able to do that for any length of time as there appears to be no provision for a heatsink (although it may be possible to heatsink it). Without a heatsink at 200 watts the output devices will simply overheat and fail- probably within a few seconds but maybe a minute or two.


IOW this kit really is for evaluation and for that I'm sure its just fine. But if I were to be building up a class D amp from parts I bought on the web and that amp were for personal use as a nice stereo this is not what I would get. One important thing missing is a bit of information about how the amp works. Is it zero feedback? Self oscillating? Stuff like that can have a huge effect on how it performs and sounds!