Interesting topology. Ever production variation-minded, I wonder how this performs with expected variations in device gain, especially over temp variations and manufacturing tolerances. And is there any predicted need to trim component values in final testing? Or, do the cookbook values and economical tolerances provide good performance? (These trims can cost boucou, or not.)
Thanks for the post. Crossover distortion can seem like an eternal enemy.
This was never expected to be in series production, however, there is no need to change the component values if the recommended genuine Hitachi parts are used. Here, the R17 multi-turn 10k trimpot serves to fine setting of the idle current, as shown in post #1. BTW, the parts used are V-MOSFETs, not the lateral MOSFETs. If you change the MOSFETs to IRF or so, then the EC must be re-calculated. Please also note that nowadays IRF V-MOS are not the same parts as they were 30 years ago and direct replacement in audio amplifiers is often impossible.
Please also note I will not re-calculate the EC parts for another MOSFETs, I am not supposed to support any commercial activities.
Thermal stability is fine if a good heatsink as shown is used. The thermal coefficient is somewhat negative, with increasing temperature the idle current gets slightly lower, but the EC keeps to distortion parameters as shown.
There is another advantage - no audible hump from speakers during turn on and turn off. So the output relay, the most problematic component of any amplifier, may be avoided for DIY use.