Here it is, pretty much done! The weather was pretty bad this weekend, so I spent most of it in the workshop, wiring everything up.
Besides the stuff I’ve already written about, there is a soft-start module (built rather messily on a tagboard), and a preamp/protection PCB. This contains Douglas Self’s anti-thump and DC offset protection circuit, a thermal cutout circuit using the spare diodes in the ThermalTrak power transistors for junction temperature sensing, and a balanced line input stage using the INA137 and NE5532.
Here are some pics.
The 10kHz square wave response, just short of clipping, into a dummy load.
I’ll do some whole-system THD measurements some other time. (I broke the Williams Memorial Oscillator. 🙂 )