What are the best GaN Amplifiers available today?

Those with Ralph's amp can do a quick test.....just remove the covers and remove all the hardware on the toroidal transformer.....lift it off the chassis and place a quarter inch thick piece of wood underneath.....put the transformer back down and listen.  This CANNOT be measured.....but it can be heard....by YOU!

Actually this one is easily measured (you don't even need test equipment, you can do it with your hand for Pete's sake) and it is audible for a simple reason.

All toroidal transformers are supposed to have a very compact radiated magnetic field, but in practice they are a bit sloppy. Transformer manufacturers supply a mounting bolt with the transformer, but that bolt is always been a regular steel bolt and is magnetic. If you use it to install the transformer, it will be a magnetic short to the transformer. So you'll find that it heats up more than the transformer itself (you can feel this with your hand... you can see how laughable the idea is that this can't be measured 🤣). So its easy to show the difference in temperature and output voltage of the transformer when the magnetic steel bolt is replaced by a nonmagnetic stainless part.

We've been doing that for at least 30 years.

Fun fact: the bolts holding EI core (conventional) transformers together are also magnetic. They are usually insulated from the metal of the transformer and this does mitigate a lot of the magnetic load they place on the transformer core. But not all of it. You can reduce the temperature of a conventional power transformer by using non-magnetic stainless bolts (don't forget to keep the insulators!) and you can increase output power in tube amps slightly by changing out these bolts in output transformers for the same reason.

You can see here that someone claiming this can't be measured hasn't even bothered!

The issue with measurement is often figuring out what to measure, and then sorting how. For example, if you want to measure the effect a fuse or power cord has on an amplifier, you don't measure that fuse or power cord- you measure the effect on the amplifier.

Similarly if you think that a certain tweak has improved the bass in your system you demonstrate this by doing a frequency sweep in the room, install the tweak and measure it again. A customer of ours used this technique to show that a certain filter capacitor he had installed in a power supply was not only improving the bass but also reducing distortion. He was able to show a correlation between the perceived improvement in bass and clarity of the system and his part replacement in this fashion; that the perceived benefit was more than just expectation bias.

I can go on with other examples but you get the point. If you hear a difference, and especially if others report the same difference, then if you think about it you can probably figure out why that's happening and measure it. But you do have to think...

I remember very clearly the first time I heard a power cord make a difference- I was at CES in 1990 and heard a set of Magnaplanar MG3s that had been modified with a wood frame made by George Cardas. It was an impressive frame and did wonders for the speakers. I asked him if I could play our MA-1s on them after hours, he agreed and we made it happen. The amps seems to have a prodigious ploddy bass on the speakers; George suggested a pair of his power cords, which we installed. The bass was instantly improved! Switching back and forth the difference in the power cords was not subtle. I bought the pair of power cords on the spot.

It really bothered me that I could hear this but there was no clear cut explanation why, other than the mysterious claims that so many cable producers make. Turns out it was something simple: voltage drop across the power cord, easily measured. I sorted this out by measuring the output power, output impedance and distortion of the amp, which led me to measuring the input AC voltage at the IEC connector. Voila!

Power cords are one of those tweaky things that a lot of people over on ASR will deny has any effect on a system's performance. Power cords are subject to Ohm's Law like anything else. When I see that kind of denial, I like to ask if they caused their hand to move and make the measurements they laud so often, rather than just blindly making a pronouncement. If there's no measurement they are no better than the subjectivists they denigrate.

The only picture that I see of the inside of your amp is when you did the inteview for the SF Audio Society.  You show the proto amp and it shows a steel plate on top of the transformer (or is that non magnetic stainless steel?) and a bolt through the transformer.  Are you still doing the same now?  Turns out that even a NON  MAGNETIC BRASS BOLT will also completely mess up the sound (I discovered this just about 5 years ago....I thought, like you its because its magnetic....turns out any CONDUCTIVE material does the same sonic degradation.....plastic bolts are fine).....and of course, a steel plate on top of the transformer. also completely messes with the sound....and it also sounds best to get the field away from your chassis.(whether aluminum or steel)....this is why you glue the transformer on top of wood.  You can hear all this.  So, if you can? measure extremely small voltage output difference or extermely small differences in heat.....please explain why you would hear this as a SIGNIFICANT difference in sound.   You cannot....if you lowered the voltage of your power supply by one volt it would not change the sound of the amp (I am sure you will argue about this).  The sonic difference in removing all the hardware and floating the transformer above the chassis is that the sound is more open, more airy....more dimensional...more pure.  So, do you float your transformer in the air with no conductive material around it?  Please, do some serious listening tests.....you will see this is way more complicated than "a magnetic bolt versus a non magnetic bolt".

Your rant about the power cord is complete poppycock.  You have posted about this before in your defense of measurments.  Of course, larger power cords have lower resistance....everyone knows that.  However, ALL power cords using the same gauge sound different from each other and one brand of 14 guage cord might sound better than someone elses 12 gauge cord.....this is common knowledge......Is it your knowledge?  Or do you think you just need a large power cord and be done with it.  If all we needed is low impedance we would all have 4 gauge power cords.  There are cable manufacturers that claim that the connector makes more sonic difference than the wire they use (very expensive wire).  Can you measure the resistance difference between a home depot connector and a Furutech?.......maybe......and if you did measure a milliohm difference....is the one with lower resistance the best one sonically? 

A few years ago I manufactured a dozen amps using highly modified IceEdge modules.  One of the first AC mods I tried was to listen to various AC inlets.  First I tried the $1 Shurter inlet that many serious companies use.  Then I tried the same inlet but Cryoed by Take five audio in Canada....$2.49 each......it was noticeably better......then I tried the Furutech $28 inlet that was pure copper, gold plated, cryoed and demagnatized......sounded much better again.  Then I tried the more expensive version of that connector that has the specail plastic and Rhodium plating......this thing was forward and zippy.....not musical to me.  However, some say you have to burn them in for 400 hours to really hear them.  I don't have that much patience.....he he.  So, I sold the amps with the cheaper Furutech and everyone was happy.  So, how do you measure the differnces in AC connectors that can give us a reliable way to buy connectors?  You cannot.  This game is so much more complicated than distortion measurements, heat measurements, voltage measurements, resistance, capacitance and inductance.  This game is infinite.....and the only way you know anything about sound is to LISTEN.

Ralph would have us all buy 4 guage power cords and use whatever for line level (Mogami is fine, with him....a friend of mine started with Mogami and thought is was good...then he tried two others that BLEW away the Mogami).  He has said over and over that balanced cables make no difference in sound.  Even his customers hear otherwise.  You have to listen to know....you have to listen to know.....and listen with an open mind.....an open mind.

I will stick with Mr. Ralph’s advice over some tweaker. 

Do not follow/believe someone.  Think for yourself.  Try out various things and find out what is true.....FOR YOU.....on your system  What is stated on this or any forum are just words......you will know with your own ears....what is real.

A new design must be made with a complete set of measures in mind...This set of measures are trade-off choices...

No design is perfect...

But designer dont tweak by definition...If they do they must integrated their tweak in the design... With or without set of measures but more often then not designer are engineer and physicist in some case  as for my headphone, they dont tweak, they use well known scientific principle and they apply it ...

But this headphone for example so innovating and amazing it was designed needed some modifications FOR ME : I throw off the protective plastic thick grid, i changed the volume of the shell chamber by using other pads than the original one, I put inside it two products to damp its vibration... After that and some other rectification their design was IMPROVED for my ears...So much so that upgrading it appear preposterous to me...

I respect a lot Dr. Gorike the physicist who design this marvel... But any design can be improved... But i will  not play with amplifier electronics components by lack of competence and it seems to me less necessary  But i even tweak my Sansui Alpha for the better with various minerals OUTSIDE of his body 😊... No serious designer will do that or advise such a "ridiculous thing" ...

Designing is a serious enterprise with his own ethic and secrets...

Tweaking a component if the user like to experiment is always possible...

Anyway any system must be embedded mechanically , electrically and acoustically ... These controls can be methodically applied or applied discretely and called "a tweak"...