[Tyson]

If one reads the links posted regarding GanFETs,  they make the same argument outlined here.  They have much different behavior than MOSFETS.  GanFETs have the linear behavior of tubes, while maintaining control of speakers like SS. 

That's probably why I like the sound of the GanFETs so much (as I posted on the first page of this thread).

[Freo-1]

That's probably why I like the sound of the GanFETs so much (as I posted on the first page of this thread).

Which ones have you listened to?

[goryu]

 

On the topic of GaN amps- interview with Purifi designers:


Lars:  We’re as fanatic about audio quality as anyone else, but because we’ve got feedback down to a T now we’re not forced to resort to higher switching frequencies.

 

Bruno:  If we need to be geeky and I guess that the folks who are going to read this interview can handle that -eh Thomas?- lets grab the specs for the FET in our 400W Eigentakt module and its closest GaN equivalent. So that’s the FDP42AN15A0 (OnSemi) on our left and the EPC2033 on our right. Rdson: 36mOhm vs 7mOhm. Clear win for GaN here.

 

Lars:  It’s also got a higher current rating (24A vs 48A) so if we want to be fair we should be scaling by about 2:1

 

Bruno: Oh erm well, that’s still a minor win for GaN because after scaling it’d come up at 14mOhm. Gate charge is of course magnificently low (30nC vs 6nC after scaling) so driver losses would be low and you can turn them on fast. GaN also has zero Qrr so you can do that if you want. But the main thing that sticks in my throat here is output capacitance. Our good old FDP42, which is from 2002 mind you, has an output capacitance at 100V of 70pF whereas the EPC device puts in a whopping half nanofarad (or 250 puff after scaling). That means your idle losses will go up, or you will have to increase dead time to allow the output inductor to recover the extra stored energy at its leisure. And isn’t it just idle losses that more or less determine real-life power consumption in full? And if power consumption isn’t something to care about, why not just stick with class A…?

 

Lars:  And high dead time combined with high switching frequency sounds even less attractive. That just increases open-loop distortion.

 

Bruno:  In applications like motor controllers and high density SMPS GaN and SiC devices are a breakthrough, mind you. It’s just that audio is this weird application where average power is very low and where dead time actually affects performance.

 

Lars:  And GaN is going to mature so this picture is bound to shift at some point. Just not now.

 

Bruno: True. On the other hand, silicon is doing the same. More recent devices are getting frightfully close to GaN. Sadly they only come in SMD packages that require fairly expensive methods to get the heat out. Like most GaN devices. It looks terribly ancient, but the good old TO220 package is still a neat compromise in terms of performance for the price.

 

Lars:  It’s just a game of tradeoffs. The fact that we’re using normal parts, and the reason why we chose to do so doesn’t make for a sexy story. We all like to believe in a magic bullet but when you’re an engineer you have to make choices based on tangible grounds. So the sexy story we’re trying to push about Eigentakt is that we think it’s a bloody clever design.

 

Read the full interview here:

https://audiophilestyle.com/ca/bits-and-bytes/purifi-audio-and-the-audiophile-style-readers-qa-with-lars-risbo-bruno-putzeys-r815/

 

 

[Freo-1]

Some good information posted.  Having said that, can take issue with some of the assumptions.  For example, Devialet Hybrid Class D solution for current, while using Class A for voltage,  sounds as good as any amp solution available,  and many would argue maybe better than any straight Class D solution.  It's certainly up for debate.


Need to hear for myself how this GanFET amp sounds.   To me, the interview didn't adequately address open loop and the lack of feedback performance of GanFET.  Other engineers have seemed to address the design issues rather well.

[Tyson]

Which ones have you listened to?

The GaNTube.  I didn't think it sounded 'like a tube amp' but it did sound better than any other class D (switching) amp I'd heard.  The DAC Maraschino's also sounded good, IMO, but I felt the GanTube was better.

[Freo-1]

The GaNTube.  I didn't think it sounded 'like a tube amp' but it did sound better than any other class D (switching) amp I'd heard.  The DAC Maraschino's also sounded good, IMO, but I felt the GanTube was better.

Cool.   

[Freo-1]

The amp is scheduled to arrive tomorrow.  Looking forward to trying this out.


Because the tube monoblocks on hand were transformed when using the Chord gear, hoping to get similar results with the Gan400.

[Freo-1]

Here's another article on GanFET:


https://www.eeweb.com/how-to-gan-egan-fets-in-high-performance-class-d-audio-amplifiers/

[Freo-1]

The Gan400 arrived today.  Took a little time to get the subwoofer gain set correctly (SVS PC4000).  Once that was achieved,  have started to conduct listening impressions. 


Initial impressions are VERY positive.   Listening to the Berlin Philharmonic 25th anniversary DVD set (2011 disc),  I was floored.  I have found symphonic music is where the rubber meets the road regarding stereo reproduction.  Many well respected setups have one or more issues with full bodied symphonic music. This amp may be the single best amp I've heard to date.  String definitions are very accurate sounding. Dynamics are first rate,  and horns sound damn near real. 


I tried the various sample rates from the M-Scaler,  and the deltas are readily heard as one steps up the sample rate.  It's more noticeable with this amp than with my other amps on hand, and it's not subtle with this amp.   The Chord TT2 DAC/Preamp has never sounded better than it has with this amp. 


Listening to this setup,  I can understand why some audiophiles go crazy for SET triode sound.  This amp has a lot of the SET sound in the midrange,  plus the authority of SS in lower octave.   The treble is amazing,  never heard it this clean and detailed.   Much of this can be attributed to the very low feedback design. The GanFET speed is clearly noticed here with transients.   Combine that with the superior signal input from the Chord setup, one gets reproduction that is closer to live than previously achievable at any reasonable price point.


I'll need to give it a few days of critical evaluation to see how it sounds over time.  Usually,  one does find something that could be improved (we are audiophiles after all   ).   Have to say, so far, it's been better than I expected. How much of the improvements are the amplification vs. the DAC/Preamp at 705KHz or 768khz is up for debate.   


BTW, no popping noise when switched on. 

[Tyson]

Yes, a very good amp!  I'd love to try one in my system some day.

[mofunz]

Yes, a very good amp!  I'd love to try one in my system some day.

Hey Tyson, it’s Ben H from Maine! Lately I’ve been scouring the web for every scrap of data I can find about this amp - it was a little surprising to see your username come up in my latest search. I was hoping you owned it and had written up one of your overly detailed deep dives. Hopefully you get to try one! If I do decide to buy one, maybe I’ll have it shipped to you first as community service.

Anyway, small world.

[Freo-1]

This link will explain the advantages of GanFET over MOSFETs for class D audio.  It also outlines why one should take any reviews and measurements (including ASR) with a grain of salt:


[size=78%]https://gansystems.com/wp-content/uploads/2020/09/GaN-Systems-Advantages-in-Class-D-Audio_FINAL.pdf[/size]

[goryu]

Gee, I wonder if there might be any self serving bias in their self promotional pdf?

Nothing out there in class d land measures as well as the Purifi class d amp, followed closely by Hypex ncore. As explained by the Purifi people above, current GaN doesn't really offer any tangible benefits for a class d application- you can claim they are biased but they offer valid reasons for their opinion, besides, there is no doubt Bruno Putzeys would be using GaN if it truly offered an improvement. Currently it appears to be more of a marketing tactic than anything offering a genuine advancement in class d. Like most amplifiers, it's all in the implementation. The advancements made by Putzeys in applied control theory, having developed exact mathematical solutions to the control loops, is a real leap in class d implementation.

Orchard Audio has the most accomplished GaN class d amp currently available, though it doesn't really offer anything beyond what the Purifi amp offers. There is a good review on line comparing the two amps.

[Cappy]

I'm wondering if class A/AB/H amps will start using GanFET output devices.

Apparently the current crop of GaN devices tend to self destruct when used in linear amplifiers.  I've heard this from a few designers.

From Nelson Pass:

It's possible that some more will get made, maybe by Transphorm, who
recently worked with an academic from my alma mater on a team
making SITs with Gallium Arsenide.

I wouldn't count on it though, as companies developing power semis at
this time seem to be concentrating on switching performance only, at
the expense of reliability in linear applications. I am seeing new parts
rated at hundreds of watts for switching that die at 20 linear watts.


Original link to Nelson's thoughts here:  https://www.diyaudio.com/community/threads/what-does-mr-nelson-pass-think-of-yamaha-power-amps.301653/page-2#post-5895684

[Freo-1]

Apparently the current crop of GaN devices tend to self destruct when used in linear amplifiers.  I've heard this from a few designers.

From Nelson Pass:

It's possible that some more will get made, maybe by Transphorm, who
recently worked with an academic from my alma mater on a team
making SITs with Gallium Arsenide.

I wouldn't count on it though, as companies developing power semis at
this time seem to be concentrating on switching performance only, at
the expense of reliability in linear applications. I am seeing new parts
rated at hundreds of watts for switching that die at 20 linear watts.


Original link to Nelson's thoughts here:  https://www.diyaudio.com/community/threads/what-does-mr-nelson-pass-think-of-yamaha-power-amps.301653/page-2#post-5895684

Thanks for the feedback.  Looks like Nelson was referring to Sit devices,  but I'm not sure.

[Cappy]

Thanks for the feedback.  Looks like Nelson was referring to Sit devices,  but I'm not sure.

That conversation is about possible new SIT devices, but included is his experience trying to use current GaN power semis in linear apps.  Which doesn't work.

Basically he is saying GaN could work in classic A and AB amps, but not as currently offered. 

[Freo-1]

Gee, I wonder if there might be any self serving bias in their self promotional pdf?

Nothing out there in class d land measures as well as the Purifi class d amp, followed closely by Hypex ncore. As explained by the Purifi people above, current GaN doesn't really offer any tangible benefits for a class d application- you can claim they are biased but they offer valid reasons for their opinion, besides, there is no doubt Bruno Putzeys would be using GaN if it truly offered an improvement. Currently it appears to be more of a marketing tactic than anything offering a genuine advancement in class d. Like most amplifiers, it's all in the implementation. The advancements made by Putzeys in applied control theory, having developed exact mathematical solutions to the control loops, is a real leap in class d implementation.

Orchard Audio has the most accomplished GaN class d amp currently available, though it doesn't really offer anything beyond what the Purifi amp offers. There is a good review on line comparing the two amps.

The Gan400 sounds better than the Hypex by a fair amount.  Haven't heard the Purifi, but all things being equal,  I'll take 400 watts from the Gan400 any day of the week.


The Gan400 needs to be heard to get what it's about.   I'm not sure Bruno would be using GanFETs.  They present a different set of engineering challenges,  and perhaps he doesn't wish to tackle them.  It would involve a fair amount of effort and time. 


The advantages of GanFET operation is obvious.  The speed and thermal advantages are not debateable. Would rather have an amplifier with little to no feedback that truly sounds open and transparent.  The benefits of the Gan400 are easily best heard when listening to symphonic music. 

[Freo-1]

That conversation is about possible new SIT devices, but included is his experience trying to use current GaN power semis in linear apps.  Which doesn't work.

Basically he is saying GaN could work in classic A and AB amps, but not as currently offered.

Hmm. Thanks.  Guess it isn't worth the time and effort,  as the industry is moving away from linear amps.

[goryu]

The Gan400 sounds better than the Hypex by a fair amount.  Haven't heard the Purifi, but all things being equal,  I'll take 400 watts from the Gan400 any day of the week.


The Gan400 needs to be heard to get what it's about.   I'm not sure Bruno would be using GanFETs.  They present a different set of engineering challenges,  and perhaps he doesn't wish to tackle them.  It would involve a fair amount of effort and time. 


The advantages of GanFET operation is obvious.  The speed and thermal advantages are not debateable. Would rather have an amplifier with little to no feedback that truly sounds open and transparent.  The benefits of the Gan400 are easily best heard when listening to symphonic music.

Sounds better? That's a subjective opinion that can neither be proven nor disproven. I prefer to stick to objective facts.

Bruno is committed to excellence. His work speaks for itself. He has the ability to use GaN if he wanted to, and he made his case in the interview above as to why he sees no advantage at present in clear and rationale terms. He addressed the thermal and speed advantages and explained the issues with them in a class d implementation.

"truly sounds open and transparent" is just more subjective opinion. The Purifi has much lower THD+N, a lower noise floor, and by any measure, a cleaner output, than this GaN amp. How much "clearer" can you ask for?

Seems you are stuck in the past with your perception of feedback. Maybe read Putzkey's papers on the subject.

[Tyson]

Sounds better? That's a subjective opinion that can neither be proven nor disproven. I prefer to stick to objective facts.

Bruno is committed to excellence. His work speaks for itself. He has the ability to use GaN if he wanted to, and he made his case in the interview above as to why he sees no advantage at present in clear and rationale terms. He addressed the thermal and speed advantages and explained the issues with them in a class d implementation.

"truly sounds open and transparent" is just more subjective opinion. The Purifi has much lower THD+N, a lower noise floor, and by any measure, a cleaner output, than this GaN amp. How much "clearer" can you ask for?

Seems you are stuck in the past with your perception of feedback. Maybe read Putzkey's papers on the subject.

Great, no need to ever listen to 2 amps side by side anymore.  Just look at the measurements and pick which one measures better.  Makes life so much simpler.

But what happens if I buy a Purifi amp and 6 months down the road find I'm not listening to much music anymore, because my amp is making all my music sound like a constipated mess?  Which is pretty much my experience with all Class D amps (including the Hypex and Purifi amps)?  What then?  How will these measurements help me when that happens?