I have recently had some prototype circuit boards made using the ECX10N20 and ECX10P20 lateral MOSFETs. I have for the most part copied the original B&K st-140 circuit boards. I only made Minor changes like adding additional filter caps, and I used larger copper traces and 2 layers instead of the original single layer board. I used all quality components like dale resistors and nichicon caps. The amplifier sounds great compared to the original except I am getting a audible clipping sound and fairly high volume levels. I accidentally figured out that if I place my DMM leads on the source of the n channel MOSFET and the ground connection on the circuit board the problem completely goes away. I don't understand what's happening. I'm not a engineer just a electrical technician.
