Hi I am working on a project using a triac to do phase control dimming of 120V ac powered devices. I recently translated my project from perfboard to SMT using an SMT fabrication service. The project appears to be working correctly, except for the snubber filter section. Despite having a snubber filter, I can see on my scope that the ac output still has a hard cut-in in the middle of the waveform and I can hear an audible buzzing from the board at dimmer settings where the ac waveform turns on mid cycle. I am testing with a 43W incandescent bulb.
I have checked that the components are the correct value and were installed correctly. Is there anything in component selection that might cause this? Here is the relevant schematic section showing the triac and the snubber filter:
Here are the components I picked for Q1, R13, and C6 respectively: