H5 C1 volume fix.

[exxos]

I noticed that while building my second board that the volume seem to have a AGC ( automatic gain control) going on. So I removed the amplification from the second audio stage (basically turning the volume down) and the AGC volume problem on my TV went away. Basically my TV must have some sort of "volume overload protection" going on.

The fix for this is to solder over the resistor as outlined below. This will of course limit your volume from about 2V p-p to 1V p-p. Volume level does not sound that loud on my TV reduced. But it obviously does not like it higher. So possibly other TVs might also suffer from AGC or simply distortion. Even 1v p-p is still rather high for audio output.

I am classing this as a optional fix.

Simple solder over the highlighted resistor to reduce the volume level.

fix.PNG

Incidentally the original STFM circuit was 2v p-p or thereabouts. Though I do not think chip-music and such that the volume was affected. It wasn't until using the MIDI synth module it was noticed. Likely because of the deeper bass notes.