The use of GaN-based power transistor tech is now emerging for Class D audio power amplifiers. Seems appropriate to devote a forum thread to this topic. At least 3 companies have commercial class D amps in their books:
Merrill Audio, with their model Element 118 ($36k per monoblock, 400 W into 8 ohms, 800W into 4 ohms), Element 116 ($22k per monoblock, 300 W into 8 ohms, 600W into 4 ohms) and Element 114 (coming soon). https://merrillaudio.net
It is not clear whether the cheaper Technics is a digital amp or a class D amp. I will use these terms because it is very clear. A digital amp takes the analog signal and coverts it to PCM though an A2D converter and then converts it to PWM. A class D amp takes an analog signal and converts it directly to PWM. The only way I found out the larger Technics amp was a digital amp was to read the very clear review I linked to.
A class D amp is class D whether or not its driven by a DAC. Pulse Width Modulation is an analog process that some Class D amps use. But that is only one encoding scheme and class D amps have at least three; the other two are Pulse Code Modulation and self-oscillating.
There is no such thing as a ’digital amp’. All ’digital amps’ are actually class D amps with a digital front end.
What it says is that the "output stage" is class D......it does not say how it is driven.
Strewth!! it’s Class-D using GaN technology and Jeno (Jitter Elimination and Noise-shaping Optimization) just like it’s $20k Technics big brother the SE-R1!! doesn’t mater if it takes a digital input or analog, it’s still a Class-D amp. https://www.technics.com/us/products/grand-class-g30/network-audio-amplifier-su-g30.html Good luck with your venture??.
I’ve noticed a pattern, that the only ones whinging, or finding invisible problems to turn people off with the GaN technology. Are the ones with "some sort" of vested interest or ownership in the older Class-D topology, that are built around readily available "off the shelf" Class-D modules, be they Hypex, IcePower, Pascal, Tripath, or Sanway ect. I think we would see a different story with them I think, if a complete GaN based module was available to all, for around the same price range as the older technology above.
+1, George. This thread is devoted to only GaN-based transistor tech for class D audio amplifiers. Please let this thread grow organically with that purpose in mind.
It is hard to deny what I have heard 1st hand from GaN. My buddy has a pair of ADG Vivace monoblocks in for review. These are 15k pr. They sound REALLY good. Excellent bottom end control. Fast, very accurate, quiet and very cool running. They have gone side by side on his reference 625s2s which are magnificent A/B examples. I think the future is here, needs some refinement but no doubt in my mind, there is something to benefit with GaN.
OK, I didn't want to weigh in because I get hot under the collar with knowitalls that have never owned nor listened to that of which they speak. So I will in usual style speak about ONLY things that Ive listened to in MY RIG in MY HOME. anyone else is just bumping their gums from boredom. or guessing, speculating, fantasizing, or otherwise just stroking. I make it my business to speak from first hand experience, anything else regarding ones opinion of the efficacy of any given product is not welcome in HiFi as far as I’m concerned. Time to change the playing field, and make forums something respectful and honorable. Unless you wish to kill the industry which is very much the way it looks. Newcomers read crap like this and run away from us. so gather up sit down and listen.
I have 4 AGD monoblocks as we speak, because I biamp. I also have 2 Jeff Rowland 625 S2’s because they are a top level class AB reference, I have 2 Jeff Rowland 535 amplifiers since they represent the first class D to fool me into thinking I was listening to Class AB. these can be bridged for 900WpC. Next week I will receive a tweak from Jeff that catapults them to new levels once bridged.
So I speak from experience and furthermore I Prove myself by making videos and recording the differences in sonic so you guys can hear for yourself. OCD Hi Fi Guy on youtube. There you wiill find the veteran industry guy that is paid by no advertiser, and owns my company, so I say it the way it is. So to give Ceelander what he asked for in the first place, I will share my experience with these amps.
The AGD GaN amp is unlike anything Ive heard so far in HiFi. It literally took me aback whereby I had to relax and calm myself to wrap my head around what I was hearing. Complex music at high volume with the most articulate top end ive ever heard. This means things that normally can be a touch smeared are now perfectly discreet all in their own place, to me this is an indication of stunning speed and accuracy. I played torture test pieces that normally hurt, that were so clear without edge it bewildered me. This is something I did not think was possible. I love defined leading edge in my playback. It is the very thing that brings clear 3 dimensional rendered images into my soundstage. The little thing that brings life, and I mean life in the way that you sense a human in the room with you. Normally this comes with borderline stridence. Never have I heard a top end so defined and smooth at the same time. (speakers are heavily modified Magnepan 3,7i with custom sub towers on channel 2 crossed at around 90 with a 12)Bass.. let me be a New Yorker for a second.. You can friggin fuggedaboudit. Tight and tonally correct, musical even. Mids clear and liquid to the point that I got nervous about my beloved Rowland Model 12 .. when I first tried the AGD’s I had 4 Rowland model 12 monos. I got so unnerved by AGD, I sold them and bought a brand new pair of 625S2, the amp that in Jeffs words when asked replied "Ive taken Class AB as far as I can take it" even if I beat these amps out I’ll keep them as my example of AB at its highest.
im starting to get freaked out because this is getting very long and ive erased full pages like this so I’ll post and start a second
I suppose I should add the AGD is not made from any silly module whatsoever. Modules are made so guys that cant design digital can still make amps by creating an input section. Ive got no respect for modules in a box, unless I hear about some very innovative front and with some very interesting software they wrote.
(here comes a rant, youve been warned) I must say something about this amp (not the guy) the top of the line Merrill at 36 K per box.. dont you guys think this kind of crap is ruining the industry ? Dosent Dan have an amp thats near $200K ? Give me a break.. Those are the designs of scared people that thier meal ticket is ending so kick some Dubai Sultans under the robe before they go. Cash grab before the grave type thing.. Because it is ending. HiFi the way youve known it is on its way out, and class D is coming whether you like it or not. Eventually EPA will stop the production of Class A as an energy waster, just wait and see.. Finally back top Merrills top of the line is it just me or is that 36K box made from plate aluminum screwed together with more plate in smaller pieces put on the sides, 2 squiggles put on those plates to distract design neophytes, a set of outriggers in chrome which serve no mechanical purpose (they are meant to keep tall things from tipping over) again, distract the folks that dont know design, then make it a weird color. To me this company has just exposed how little they know about aesthetic, or how strapped they are for cash to do proper aesthetic, but to have the Gall to price it at $32K ?? now you are going to make true lovers of high design blow off our industry. Look at the AGD, 1 inch thick billet walls with no seams, and a smoked underlit Lexan top with a freaking output stage in a KT88 envelope !! Say what ?? yes, he "ship in a bottled the complete output section into a empty KT88 tube and its pin correct for operation. This is an infinite number of iterations you can easily do yourself. You dont buy a new bigger amp, you buy an output tube with a digital GaN engine inside. Theres no way to blow these but lets say you invent one.. so what ? change the tube out to fix your blown amp. If you dont recognize innovation when it kicks you in the shorts then I can not help you. This amp is clearly something new. Nobody has ever seen anything close. you want a plate aluminum amp screwed together for $36K as something new, I honestly don't think that's ever been done either.. which type of innovation do you respect ? Lets get priorities straight people ! Look at Jeff Rowlands amps, I dont really think the comparison is fair because he still uses silicon, but I respect his method. He represents the tried and true. he will let everyone else step on their noodle while he sits back and watches and calculates. He moves on well proven tech only. Partially from going to early on new tech in his earlier years. Older and wiser. His 535 are only $6K, crap, his 125 are $3K but still come out of a machined single block of aluminum. There is no better chassis ive ever seen than milled billet. I will keep most of my focus on GaN since I abide by the posters desires, but These GaN amps better my Class AB Rowland amps in the clarity and articulation of upper mids and highs on complex music and the bass is out of this world, yet there is one area the Rowlands dominate, and I will check this more, and thats the upper bass, lower mid area.. Male vocals for instance.. a little fuller in the body in that specific part of the freq range only. I imagine tuning may fill this area of the AGD, but if I did not AB , I would be extremely happy with AGD Merrill is the only other contender with GaN and Id be happy to compare. I honestly dont think manufacturers even care about these little squabbles
But These GaN amps better my Class AB Rowland amps in the clarity and articulation of upper mids and highs on complex music and the bass is out of this world
I don’t condone dealers giving their "two bobs worth" on what sound better than what, especially if they sell the equipment, but this is a dealer that sells Rowland Research
The little thing that brings life, and I mean life in the way that you sense a human in the room with you. Normally this comes with borderline stridence. Never have I heard a top end so defined and smooth at the same time.
This is what Gan Class-D Technology is all about, getting the upper mids/highs right, that so many have questioned about, with today’s/yesterday’s Class-D technology.
I would be extremely happy with AGD, Merrill is the only other contender with GaN and Id be happy to compare.
You could probably add both GaN based Technics to that also, the SE-R1 and SU-G30
I',m back, after just completely putting the GaN amp at a disadvantage. Its 100W at 8Ohm and I put one amp each channel whereby I took the midrange driver lead from my outboard crossover and put a full .7 Maggie on it rather than going to the 3.7i panel. My purpose was to find the line of the AGD and I did of course. Whats nice it the channel just stops music, when you turn it down it comes back. So you will not damage the amp or speaker with this kind of protection so thats cool. I would say that the Vivace monos would be perfect with speakers 90db and above. The articulation and quickness would be very well matched.
By the way, I'm not a typical "dealer" per se.. Im a manufacturer, founder of Verastarr AudioFoil Cables. Thats my main thing but when my users want to buy ancillary equipment, I like to be ready to serve them without skipping a beat, so if no client is asking, I'm not advertising gear whatsoever, unless its used or demo, I'm moving out. George, isnt the Technics like $30K or something ? Anyways I'll go back to testing the GaN with something its own size to be fair.. So like a Rowland 125 actually at $3K.. seems off but its the truth..
George, have you spent any time with Rowland amps ? Forget continuum, it seems to be a sore spot,(im sure there is more to that design we cant see and I'll share any info I get, plus If I needed to i could expose a myriad of other top level HEA companies using drek inside. Ive got to believe there is more to it because if youve ever met and spoken to Jeff, hes not the sheister , hustler type whatsoever, its quite the opposite. As a total kid/ newbie, I remember Jeff was the only HEA Icon who looked me in the eye and listened to what I was saying. To this day he still does this for anyone that speaks with him, which shows great respect for his fellow human being. I also know Mark Levinson and God Bless him hes got a different way, 100% entertainment for me to watch, but Mark is from the streets of NYC, Jeff is up in the mountains.. so you catch my drift... You do however make an interesting point.. I will get to the bottom of it. Meanwhile I'm happy to ship one of Jeffs amps for you to try out in your rig, I am a real picky SOB and they are very well built and great sounding. All the best.!
I',m back, after just completely putting the GaN amp at a disadvantage.
Its 100W at 8Ohm and I put one amp each channel whereby I took the
midrange driver lead from my outboard crossover and put a full .7 Maggie
on it rather than going to the 3.7i panel. My purpose was to find the
line of the AGD and I did of course. Whats nice it the channel just
stops music, when you turn it down it comes back.
Mike Powell wanted me to correct my OP regarding the power output of the AGD Vivace monoblock amps. Unfortunately, I can’t edit the OP once someone responds. While the AGD Vivace can output as much as 200W into a 4 ohm load, I interpret this to mean output power at clipping. The nominal power output is 100W into a 4 ohm load at the rated distortion specs. See the technical specs page from the AGD website:
Regarding the cost of the Merrill amps in my OP, I incorrectly stated these prices as per monoblock chassis. I corrected this pricing error to reflect the price per monoblock chassis PAIR.
@erik_squires If you take a look at OCD Guy HiFi videos on YouTube you will see Mike P's audio setup. I think if yo visualize his system you will understand.
Hi Guys and greetings from Germany! I'm new here this is my first post in this forum. While surfing around through the internet looking for news about Class-D amps I found this thread and somehow had the feeling to add a comment. Because luckily I'm one of the 1st owners of a pair of the AGD Vivace GaNTiube monos here in Germany. When I finally got a pair of the "ready to release" version of the GanTubes I was blown away and could not stop to listen these little things. I must say I was used to a Nelson Pass F5 Turbo (pure Class A) and I always were happy with the F5 but the GaNTubes have blown it away. In every aspect, especially the mid-highs they distribute so much... lets say 3D sound. I was just astonished about the difference to my F5. It feels like you can grap every single instrument or singer in the room. Just fantastic! If someone has the chance to listen to the AGDs I can only recommend to take the time and do so, it will be a great experience. I'm driving a 8Ohm broadbandspeaker-Expo horn with 93dB efficiency. And it perfectly fits together. Of cource 15k $ for pair of the AGDs is a lot of money but for HiFi lovers in my point of view worth every single Cent. Cheers,Mallard
So nice to see a GaN thead with such a wide range of comments. I will add a few factual items here for the benefit of the readers and non circuit designers. First of all Class D has been around since the late 1950's. The concept of Class D could not be fully realized until the semiconductor technology caught up with the Theory.
The theoretical assumption of Class D design is that the switching device – the transistor or tube, can switch instantaneously on and off. I will refer to the device as transistor from here on. If the transistor does not switch on and off instantly, a lot heat and current will be required. There is heat generated in the transistor as it goes from theoretical zero ohms to the off state of the transistor. This transistor acts a resistor which generates heat. The 2nd item is that the conduction will start between the positive voltage rail and the negative voltage rail as one transistor turns on and the other turns off. This causes more heat and more current to run, with potential damage to the transistors or very large amounts of heat and current flow. What Class D designs have done is to delay the turn on of 1 transistor until the other is completely off. At this point there is no processing while waiting for the transistor to settle down. This is called dead time. This is what folks call “Class D sound”. Which is quite true. One way to get rid of this was to use heavy feedback or feedforward to reduce this dead time effect. The side effect of heavy feedback (or feedforward) was sluggishness and loss of detail as the feedback loops tried to correct for this dead time.
Transistors inherently have a lot of capacitance. This is the cause of the slow turn off. The capacitance in the transistors (MOSFETs in particular) keep the charge going even though the voltage has been removed. This causes running at the top and over shoot. Hence the hard edge of Class D also. Class D typically operates at 400kHz and so RF design methodology has to now take place on the circuit boards, wires, components and the whole design. A simple item like having a trace on the top of the board and the bottom of the board created a capacitor that could now affect the sound.
The overshoot is a common cause of the hard edge found in a lot of solid-state equipment. That is because the speed of the solid-state transistor led to all sorts of parasitic capacitance's to come alive. As mentioned prior, board capacitance, component capacitance, even the via’s on a circuit board make a difference now. The overshoot would suppose the frequency be in the 100kHz or higher. RF design is a key factor in Class D and in making good solid stage equipment.
What GaN (Gallium Nitride on silicon or Gallium Nitride on Silicon Carbide provide is 1. Ultra-fast switching speeds 2. Almost no overshoot and ring 3. Minuscule parasitic capacitance on the device. 4. Much greater efficiency of operation.
I can only speak for the Merrill Audio amplifiers at this point. 1. There is zero dead time. So it is smooth and you cannot tell or scope any switching. 2. There is zero feedback. Since we don’t have to correct for distortion or overshoot or deadtime. This results in pure detail and air (assuming the track has all of this recorded in it). The difference is quite stunning. 3. There is miniscule parasitic capacitance and inductance. There are probably have more capacitance in interconnects. 4. The wasted energy is minimized and the design is very efficient. Hence the amplifier operates at a stable low temperature, keeping all components around it operating at a low temperature also. This temperature stability means the operating amplifier approaches theoretical design. There is not thermal compensation required or degradation of components due to heat or thermal gradients of components to worry about. While green is a side benefit, the actual benefit is stable operation of components. This is big as inductors, capacitors and resistors have heat coefficients (positive and negative) and have different values at different temperatures. From a sonics standpoint, the new Merrill Audio ELEMENT series are easily an order of magnitude better than the VERITAS. But don’t take my word for it, go listen to them yourself. Take your amplifier and do a direct A/B comparison.
GaN transistors – first commercially available in 2010, will certainly become more pervasive as the costs come down. GaN material was used in LED’s for over 2 decades.
GaN transistors can be used for any class of amplifier. It is not limited to Class D or other switching designs. It is commonly used in the Cellular industry which was the first to take it up as an amplifier. This is because of the very fast switching speeds and power handling capability of the GaN transistor. It is excellent for operating in the Gigahertz range.
As the volume increase, production gets better, the price of the GaN transistors will come down and you should see them used ubiquitously, much like a silicon transistor today.
I don’t give out the details on my component designs, and that will hold true here also. And as noted in this thread, it matters what it sounds like, not whats in it. A Bugattis cost money and not everyone can afford one. So the best sound for what one can afford or is willing to pay is where all of us will land up.
Here are some of the early reviews and more to come from HiFi Plus, Enjoy the Music, Positive Feedback and so on.
Brutus Award , Positive-Feedback.com editor David Robinson, “After starting the listening sessions, I still didn't realize that they were Class D…at first. I really liked the initial impression that the Element 118 created in me: very fast transient response, clean, transparent, detailed, and lacking no dynamics with key recordings that I always use. Then I walked over to the amps to assess the heat being generated, and was startled by the fact that the 118's were cool to the touch! "Damnation!" says I, "The bloody things must be Class D!" They are, but with state-of-the-art design and execution that puts Class D into my top-o'-the-heap class of true reference amplifiers. Details will follow in my review, which I hope to have done in January or so of 2019. Stay tuned for that one…the Element 118 is serious stuff!”
You can also look up my thread on “Merrill Audio ELEMENT 118 on Tour” to see more reviews first hand. Some of the speakers used are high efficiency horn speakers. Also look for reviews by Kansas City Orchestra percussionist in other forums.
To summarize, it is not the topology that matters, it is the actual build, fit and design. The ultimate test is the listening test. Until one hears A/B comparisons and actually hears the component, it is very hard to speculate how good or bad something is by just the marketing material or chatter.
The overshoot is a common cause of the hard edge found in a lot of solid-state equipment.
Not even apples and oranges, this is apples and couches.
What evidence or experience do you have that this particular issue is indicative of this audible problem in a linear amplifier?
Next, since these overshoots are at an even higher frequency than the switching speed, maybe by 10x as much. A 400kHz switching speed, with some ringing, would probably be in the 4 MHz range. Based on what experience do you attribute this particular issue to a particular sound quality in what exact Class D amp?
Because the last thing my Class Ds have is hardness, did I get lucky?
mallard1 I was blown away and could not stop to listen these little things. I must say I was used to a Nelson Pass F5 Turbo (pure Class A) and I always were happy with the F5 but the GaNTubes have blown it away. In every aspect, especially the mid-highs they distribute so much... lets say 3D sound. I was just astonished about the difference to my F5. It feels like you can grap every single instrument or singer in the room. Just fantastic! If someone has the chance to listen to the AGDs I can only recommend to take the time and do so, it will be a great experience.
And welcome to you. This is a very eye opening review with comparison to a very highly regarded Pass amp. If this type of review/comparison stays consistent with other reviews to come, looks like my boat anchors may go up for sale before the want/need drops out of the market for them.
PS: Good to see Merrill audio giving us info on his GaN Element range, and why GaN technology Class-D with it’s superior switching speed and dead time is going to finally bring Class-D into the hiend proper, with no question marks on the upper mids or highs.
+1, Mike (OCD HiFi Guy) Powell, for his contributions here. Mike always impressed me as a straight shooter, no bs, kinda guy. I’m one of his clients, so call me biased.
+1, Teo_Audio, for correcting his now-deleted post (see 👇🏻). Fluoride in our (US) toothpaste is nasty, too. Feds have no problem feeding the health benefit bs line to us. Lol
Note having the fastest car does not mean you automatically win the race. It is but a tool of many tools required to win the race. GaN transistors is not a guarantee of good sound but one of a lot of items that will get you there.
merrillaudio Having the fastest car does not mean you automatically win the race.
GaN transistors is not a guarantee of good sound but one of a lot of items that will get you there.
Would you say that it's needed to get you there at the very front, and without it your just an also-ran? (for the time being)
" GaN transistors – first commercially available in 2010, will certainly become more pervasive as the costs come down. GaN material was used in LED’s for over 2 decades. GaN transistors can be used for any class of amplifier. It is not limited to Class D or other switching designs. "
Actually the first part is true 100% (I was in the team at IR that actually did it in 2010, maybe a bit too early ;))
The second part it seems to me not completely accurate. As far as I know, all GaN devices available in the market, sold by IFX, EPC, GaNSystem, Transphorm and few minor others, are designed 100% as switching devices and cannot operate well at all (meaning they will most likely blow up), if operated in linear region (Class A/B or Class A amps). Moreover, in order to make anything with a full symmetrical configuration, needed for A/B or A topology, one would also need a P type device, something that does not exist, as far as I know, with GaN.
But again, GaN Mosfets are a massive improvement in the power semiconductor technology because they offer a F.O.M (figure of merit) much better than any Silicon based devices (this is true however in the voltage range between 100~600V, not much advantage yet below 60V at all, at least in power conversion) GaN is ideal for CLASS-D , because, as Merrill pointed out in his comment, designer can actually virtually eliminate the deadtime issue (reduced to mere few nanoseconds) and thanks to the transition time so much faster, be able to transfer a much wider harmonic content of the input signal to the output. Remember the 3D feeling in the comments of some that has actually listened to the GaN amps vs. traditional amps? However GaN alone cannot provide all the benefits, designs that operate at high frequency require a complete different PCB layout attention, extremely reduced parasitic, and as always in Audio applications, a careful selection of passive components, even more critical with GaN. So there are a lot of challenges, but not so intrinsically different than the one engineers encountered 30 years ago when the first power MOSFETs started to replace old bipolar transistors (and 30 years before when the bipolar transistors replaced the vacuum tubes). Eventually, lesson will be learnt and all the improvements will end up to benefit the customers/users of the new advanced products.
Regarding power output of the in production GaN-based class D amps, I’ve been criticized for posting what is from the manufacturers’ own websites. So this is my last attempt to compare their respective outputs:
ADG Vivace: 200W into 4 ohms with 0.1% THD using a 1kHz signal
Technics SE-R1: 300WPC into 4 ohms with 0.5% THD using a 1kHz signal
Merrill 118: 800W into 4 ohms (no THD or frequency signal data specified).
Some more info that come to the net, also i may have mentioned, that TI Texas Instruments (who also own Burr Brown) have now the rights to manufacture GaN semiconductors.
"EPC’s enhancement-mode GaN (eGaN) transistors switch up to ten times faster than silicon MOSFETs, with ‘zero’ stored charge. The increased switching speed of eGaN FETs allows amplifier designers to increase PWM switching frequencies, reduce dead-time, and drastically reduce feedback; producing a sound quality previously limited to large, complex, heavy Class-A amplifier systems.
Demonstrating the superior performance of eGaN technology with their eGaNAMP2016 amplifier, Elegant Audio Solutions of Austin, Texas, has produced an amplifier capable of a continuous power output of 200 Watts into an 8Ω, or 400 Watts into a 4Ω speaker load, with THD+N as low as 0.005% and very low feedback."
Elegant Audio Solutions’ eGaNAMP2016 Class D amplifier with audiophile level audio performance.
Moreover, this is done without the need for a heat sink and eGaN-based amplifier can plug directly into the standard amplifier implementation of many existing systems.
In addition, the higher output filter frequency makes output filter design less expensive and the higher switching frequency makes EMI/EMC compliance much easier to accomplish.
As noted, since the switching edges of the eGaN FET are cleaner, and introduce less ringing With a good layout, overshoot and ringing can be virtually eliminated [3]. With the reduction in both the output filter costs and the virtual elimination of heat sink costs, the eGaN FET-based high-definition audio system will not only sound much better, but will be much smaller, and have a lower system-level cost than the classic MOSFET-based systems.
Regarding power output of the in production GaN-based class D amps, I’ve been criticized for posting what is from the manufacturers’ own websites. So this is my last attempt to compare their respective outputs:
ADG Vivace: 200W into 4 ohms with 0.1% THD using a 1kHz signal
Technics SE-R1: 300WPC into 4 ohms with 0.5% THD using a 1kHz signal
Merrill 118: 800W into 4 ohms (no THD or frequency signal data specified).
Every manufacturer, has a different approach about how to provide (a bigger) number, when related to the output power. It is the main number that attracts first attention, and for the most part actually it means not very much, but yet that is why the temptation (thanks to the lack of industry standards) to find a point in the THD vs Frequency chart as favorable as possible, and get it as big as possible. We have chosen to provide a number, within the characteristics of the design of the GaNTube, that still has some more meaning, in relation to a power level that can be delivered within reasonable quality (low distortion) and generate a "ears-drum safe" sonic pressure, if ever used. With a 100W input signal, a speaker with even low efficiency, let's say of 87db at 1W/m., can generate a pressure of almost 110db...so...
By the way, comparing the power specs, it seems to me that the only way to get to that power level, considering the GaN MOSFETs available in the market, both Technics and Merrill amps are likely adopting an internal bridge configuration, for the power stage. In other words, with a bridge configuration, the power would have be 4x. (The load sees twice the voltage swing, and since P=V^2/R if V is double then P is 4x). The Power stage integrated into the GaNTube is not in bridge mode, it is a single stage, and for whoever is curious, uses a custom integrated half-bridge GaN Mosfet made by IR (now Infineon).
Also, I would like to share something more. When the idea of the Vivace was conceived, so to speak, we choose to go with an unique design, both for the technical and the aesthetic one. That decision was made because we wanted to convey the message that a ClassD amp can sound better than the best classic Tube amp, and actually look very nice too and different (not just like another metal box of exaggerated dimension). The aim was in principle to liberate the Class D topology from the "stigma" it has been carry-over for way too long, and for sure now, at least with GaN, without any foundation or (de-) merit; actually all the contrary. And it seems it is finally happening. In any case, what I found peculiar too, is that from all these comments, now so many, it seems only very few people actually have had the opportunity to do some true comparative listening tests. By reading the comments, whoever has done it, more and more it sounds to me like someone that "...has seen the light" (sorry for paraphrasing St.Paul...but...) So my suggestion is...type less and listen more...go get to listen to these amps!
Reading Merrills' amp reviews/comments I am so disheartened that the commenters own amps (including Merrill's pre Element series) significantly more expensive than anything I can dream about being so much better. Even the AGD Vivacies (which also have outstanding reviews) are way out of reach
I’d like to see the raw output of a GaN switch in a class d amp configuration, and find out exactly how much of that hard slewing --consists of odd ordered harmonics.
As, if the device is incapable of being linear, then ..it it very likely going to produce large amounts of odd ordered harmonics.. theory seems to say that but the design of GaN may make this problem go away. This problem that exists in all transistors up to this time.
the more non linear the gain curve of a transistor, the more odd ordered harmonics it generates. The more linear the gain curve of the transistor, the more even ordered the harmonics in it’s distortions.
This is why Nelson Pass went out of his way to have set of SIT (V-Fet) transistors made by semi-south (a manufacturer since gobbled up by someone else).
V-Fets have linear gain curves, very much so, similar to a triode tube. This is a big deal, a very big deal and it becomes that, when a person hears it..for a long enough time to understand what is going on. like intelligence, it takes different amounts of time for a person to work through--to the hearing of it. Some might never get there (cable haters, etc).
This not speculative, it’s part of the human spectrum. Until one hears a v-fet signal reproduction system, they have literally..no idea. It’s all gobbledygook and a bunch of words, until then.(of course, they need to possess the wherewithal in their personal and unique hearing and brain... and the time spent listening--- to ’get it’)
The harder (or faster) a transistor turns on or off, in time, ie, hard slewing, the greater the set of distortions produced in level as compared to the pure on/off aspect.
Using that signal (from the GaN transistor) as the basis of the sine reproduction, means that the sine, or audio waveform recovered is going to consist of a notable amount of odd ordered harmonics, which is very unfavorable to human hearing.
The fact that the GaN transistor turns off and on.. fast... and does not generate heat ’so much’ ( in comparison to fets), means it generates lower harmonics, and that may be key here. This is the whole enchilada of my question set and points/data mentioned. Are those distortions odd ordered or even, what is the mix if any... and what are their levels compared to the main switch period itself?
We do indeed hear odd ordered harmonics better, but that would be the wrong direction. We hear them and we don't like them. They are uncomfortable and don't represent or mix with our reality. They stick out. Thus, false obscuring detail. The early transistor sound.
This is an important question, it is deeply connected to the class d amplifier issue, as the prior incarnations of class d all suffer from this problem. It is why some of us are not so fond of class d amplifiers. The signal is too close to being based on large amounts of odd ordered harmonic switching reflections. We hear it and it sounds like..well.. uncomfortable, dirty, screeching, obscuring, false details and generally..... unwanted.
If a GaN transistor will not trace a linear gain curve and will not do ’gain’ and only do switching, then it may be entirely odd ordered harmonics that are generated in this fast switching time?
Which is entirely wrong for audio.
This is a very important question set about the fundamentals of the move into GaN for audio.
Lets try not to do the wrong thing again as it is economically cool (new toy, wonderment, etc) to do so.
This is the sort of stuff we missed with digital that took us +20 years to get a grip on after the fact ...and really begin to fix the the damned mess. Twenty years of crap had to come first. Let’s not do this again. We’ve already started down that road with class D as it stands....
I contacted Paul McGowan (PS Audio) about his Sellar dac/pre, and also asked whether they are playing with GaN. He said they haven't looked into it, yet. Hmmmm? They would be the likely lowest price option
Let me just say, that if the problem of non linear distortion generated has been fixed from the fet based class-D of the now..then I’m all for it.
I’ll jump of the dang cliff and dive so deep I hit the bottom and nearly die.
I wanted class D to do a new thing, to be the new better kid, but it was not. Not even close. Efficiency was there but the audio essentials, the reason for it to exist -- all of that went into a meat grinder.
The world of audio needs/desires -outside of perfectionist audio- made it so that the music was sacrificed for financial/business/sales efficiency.
It’s the same reason we ended up with digital and it took over 20 years to try and find out how to fix it after the fact. And we’re still not there.
I spent two years working on extant class D designs and correcting their flaws, inch by inch.
It all got tossed, as no matter what I did, they could not equal the amplifiers of old and current linear design. The flaws were and are fatal and endemic to the device design criteria/operation itself.
If GaN can cut the core of that flaw out, then I’m probably in with all limbs, again.
Some of us have had a more nuanced experience with Class D than TEO_Audio.... I have been listening to class D since 2006.... I have heard class D purgatory, hell, and class D heaven since then. Have been experiencing musical nirvana in my own system with class D amps since 2008.
I have also experienced for several days one quite promising GaN-based prototype amp in my system, which, because it was incomplete nd not well broken in, was still displaying some minor audible artifacts in the treble region... Yet, was in spite of this, as I said... Very promising.
So, my ever cautious inclination is to say that GaN may be, if not the only way to create excellence with class D, at least one of the emerging technologies with high potential.
As more GaN amps are released in the next few years, we might have a better idea if the potential for generating nirvana is inherent to GaN transistors, or if GaN technology per se has instead an average chance to be inside superior amps.
Looks like ADG Productions Inc will be showing off gear at APOXNA 2019. http://www.axpona.com/exhibitors.asp Schaumburg is a short drive from Evanston. 😎
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