By the way, if you are using a toroidal transformer and you use metal
plates or bolts to secure it to the chassis....you are closing down the
sound. You want your toroidal transformer off the chassis on a piece of
wood an mounted using tie wraps and glue or a wooden plate on top and
teflon screws......way better sound.
Just a FWIW: the problem you are addressing here is the mounting. Most toroid transformer manufacturers supply mounting hardware, and if you use it the transformer will run hotter than it should. This is because the mounting bolt is steel, its magnetic and while a toroid is supposed to contain its magnetic field very effectively, in practice it does not, so that bolt becomes a magnetic short. If you install one just for fun, you'll see that the bolt is running hotter than the transformer. The solution is really very simple: just use a stainless non-magnetic bolt and no worries. And does this sound better? Yes it does- we discovered this phenomena about 25 years ago and its a nice tweak to any amplifier- the sound will 'open up' a little and of course the transformer will run cooler and make slightly more voltage- both audible and measurable!
Yes, but none yet "so far" that have taken the full major advantage of
the 1.5mhz switching speed on offer when GaN Technology is used
Actually GaNFETs and MOSFETs are both capable of switch far faster than the switching speeds seen in all class D amps including Technics. The problem isn't how fast the devices are! Its how much noise is created (or not) by the switching at power; how much RFI is created, how much of this noise is then affecting other parts of the amplifier circuit, and then there is the issue of the 'body diode', which is where GaNFETs actually have the advantage over MOSFETs. This gets a bit technical, but has a lot to do with the coil in the output filter, which stores energy and then has to release it. Essentially its what is called a 'flyback' voltage (named after flyback transformers in old analog TVs), working in a manner similar to that of a spark coil in a car. In a nutshell, the output device can behave oddly- you tell it to turn off and it won't, partially due to capacitance effects on the gate of the device and partially due to the body diode of the device, which is a primitive diode formed in the passive layers of the device when its made (and I am vastly over-simplifying in this regard!!). The filter coil flyback voltage can be effectively used to kick the GaNFET into its off state. That's a more important reason to use them than their speed, since MOSFETs have made so many gains in the last few years.
An important reason to keep the switching speed a bit lower is dead time. Dead time is invariant with frequency- no matter how fast you switch or how slow, the minimum amount of dead time you will need stays the same. So as you switch faster and faster, the output device is waiting for a greater and greater percentage of its ON time. This causes distortion to go up. Its true that Technics has a faster switching time, but it does not seem to be doing them any good IMO as they are paying the price in several different ways- increased cost without increased performance due to the associated issues with speed.
