My MOSFET amplifier designed for music

To protect against the short circuit, presumably it will be necessary to sense the induced voltage across the 0.22 ohm drain resistors. What max current should the protection circuitry (I'll be using the Hifisonix speaker protection circuit) be set to trip at? Exicon EX10N20/P20 laterals have an Id max of 8A and a max dissipation of 125W
I can’t give any advice here, because сurrent protection in amplifiers for home amateur radio use was stopped installed somewhere in the 90s of the last century, due to its influence on the quality parameters of sound reproduction at high powers, and it was also claimed that it (this protection) increases the noise of the amplifier in the low-frequency range. But I didn’t record these parameters, because I don’t install this protection.
 
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To protect against the short circuit, presumably it will be necessary to sense the induced voltage across the 0.22 ohm drain resistors. What max current should the protection circuitry (I'll be using the Hifisonix speaker protection circuit) be set to trip at? Exicon EX10N20/P20 laterals have an Id max of 8A and a max dissipation of 125W
It might sound like a cop out but the Lateral FET's are extremely rugged and failure of them was never ever a worry back in the day. A single pair of the original 7A Hitachi FET's was good for 100wrms/8ohm and nearer 150wrms into 4 ohm as long as the heatsinking was OK. They are immune from thermal runaway in a design like this and they also tend to be 'self limiting' when abused.

Properly designed over current protection should make reference to the SOA (safe operating area) of the device which is a set of graphs determined by both voltage across and current through the FET. The data sheets have these. The protection circuit would include supply rail voltage in the limiting and give a higher current limit for lower supply voltages.

In practice it is just not an issue. I have my rail fuses (per amp) using 3.15AT fuses.
 
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For my education, can you explain why you are calling it a "till coil". I haven't seen that term used for an output inductor. Tried searching but couldn't find anything.
It's actually "Thiele" and is named after the guy who came up with it. The Thiele network (paralleled inductor/resistor in series with the amplifier output to the speaker) is intended to prevent oscillations due to capacitive loads. The Zobel network does the same thing for inductive loads.
 
Just curious about the use of the term "till coil".
An inductor is a coil of copper wire, right? overall such a translator))), if I don’t have time to edit, then I end up with such “words”.
It's actually "Thiele" and is named after the guy who came up with it.
came up with ? Then it’s strange, how the mathematician Bouchereau compiled an equation for the inductor. that Thiel “invented” much later. He was the first to actively use it in audio - this yes.

It is desirable that this Thiel inductor be wound on a coil in one row, so it will be more linear for audio.
 
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Almost finished now... it's alive and working! Need to tidy up the mains wiring, make a proper front panel and the input wiring with the RCA connectors at the right position (and not just stuck into some existing holes of the recycled case), and then it'll be time to give the amp a thorough listen.

Here's another 'scope shot for power-on. CH1 is the output of one channel, now only peaking up to 5V (nice!). CH2 is the relay voltage; turn-on delay takes 1.3 seconds with my circuit. CH3 and CH4 are the rail voltages, barely 33V with the proper PSU.

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And finally some more photos:

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As you say, Neville Thiele was the first to actively use it in audio - "Journal of Audio Engineering" (JAES) 1976 Volume 24 Number 1 pages 20-23. "Load Stabilizing Network for Audio Amplifiers".
In the DIY domain " Electronics Australia" magazine offered a project "Playmaster Twin 25" using a Thiele stability network. Thiele was also involved in loudspeaker research where TS parameters are used in design processes. The S is for another researcher surname Small. Since the advent of the Playmaster project Australian Electronics magazines almost invariably include Thiele stability output networks. There was an uprated "Playmaster the Twin 40 published in 1976-1977 so there is a long history of Thiele's stability network being put to practical use for hobbyist amplifier projects.
 
Thiele was also involved in loudspeaker research where TS parameters are used in design processes.
A similar inductor was used in "bridge compensation current dumping" that Walker used in the early 70s, but its application was different. Only by examining the parameters of the acoustic system can one understand that there is an equally important applied value of this inductor for amplifiers with a common NFB. Thiel became this engineer, so this is a “Thiel inductor”.