We investigated two clipping characteristics. Without a clipping protection, the amp behavior was really bad. The output parasitic oscillations are pretty common in a high feedback design; it seems that in particular the NDFL approach is sensitive to clipping. See the picture below for the amp behavior before the clipping protection (and compensation) was implemented. Hor scale: 20uS/div, Vert scale: 20V/div
After the clipping protection circuitry was installed (please note in the schematic the original frequency compensation schema, that sneaks into one of the internal feedback loops) the clipping behavior changed significantly, see below. Hor scale: 20uS/div, Vert scale: 20V/div
The clipping indicator output signal is shown in the lower trace below. This signal is rectified and processed in the auxiliary circuitry, for visual signaling and load disconnection (if a certain clipping level is reached). Hor scale: 20uS/div, Vert scale: 20V/div
The Ultimate Audio Amp
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