Stereo to mono is simple to apply to a signal that came from audio jack. But I've encountered problems with the Butterworth filter.
- R1 & R2: 1kOhm
- C1: 220nF
- R3: 68kOhm
Only the filter: works correctly.
Only the mono: works correcty.
The problem: mono + filter is only (almost) 1/6 of the maximum volume. Why? Please correct me if I've done a mistake.