Just sharing a bit of information on my recent findings;
I’ve recently completed a Performance Technique class x with the output stages a bit of similarity with this MA Audio class x, I really didn’t checked in detail the of the drive stages of the output fets but the issue was FQP12P20 vs IRF9640 & (FQP19N20 vs IRF640).

I’ve noticed the IRF9640 was used with the FQP19N20 but both uses different value gate resistors unlike the other amp that uses the FQP12P20 with the FQP19N20 (Performance Technique) with same value gate resistors......
Long and short, could the 12P20’s be sub by the 9640’s? By just altering the gate resistors value or they are totally (major) different in specs?


  • 2FC1833B-C8A7-41C7-9C0E-EB48DB9C20DE.jpg
    599.3 KB · Views: 56
  • 7A224260-0D5C-4A9B-AECD-18F05B3FA143.jpg
    631.8 KB · Views: 53