This schematic of precise measurement amplifier with HF-parallel channel was published in 1988. Parameters: 100W/4 Ohm, harmonic distortion less 0.01% at 20 kHz (limited by used equipments), low-signal band - 0-1MHZ, full power band - 0-100kHz. Tip of all transistors is substitution of original, manufactures by USSR. Why I don’t see this principal solution in power audio amplifiers ?