allright stewin, i did build this amp again yesterday, i`ll post it here the picture, today im going to finish ir2153 smps with protection too, but this smps is for irs900d with +- 75vdc vout. probably you need to check voltage at tl074 with clamp diode 5.1 and tell me what u get, what material for the core you use, with how many uh, and filter cap at output. i just use flyback trafo ferrite core from old tv which already have an air gap at center and i did 33 uh with 470nf filter cap.
i already test new one with very high volume and i dont have such as probem with rf noise at high or low freq, if you have crossover coil at your speaker, so try dont use it. sometimes damage 5551 and 5401 transistor also give some noise at output, so better check it out. sometimes ppls do mistake by put 12 or 15 v zener diode to supply tl074 will damage that transistor, so its need to be change and change clamp diode to 5.1 v.