nick wrote
My T??my or whatever it is in its case, the switch did nothing so I just removed it, waiting for my 3PDT to arrive.
The switch in the published circuit, which I presume you used for your build, switches between three different diode clipping configurations in the op amp feedback loop. The standard is two diodes in series, each way, back to back, or one diode one way and two the other or one diode each way. There should be an audible difference between the different switch settings. Certainly with the standard switch setting of two series doides each way, the clipping voltage will be about 1.4V while with one doide each way it will be about 0.7V. So if nothing else, the two each way setting will be louder than the one each way setting. I've built two Timmys recently and there is an audible difference.
