405 lines from Raspberry Pi 5

[OldTVEnthusiast]

I’d completely missed the requirement for DC bias, which explains the low sound despite there being more than adequate output from the DAC. So what is happening, is the modulator AGC reducing signal level to an expected sync level and the DC bias lifts the signal out of the expected sync area?
Anyway I’ll breadboard a DC bias stage before going for a version 2. I do have the scope but not a spectrum analyser.