what are the differences between boards 1.3B and 1.3R? I found couple capacitors added and the main change is new MIC input circuitry. Is there better sensitivity with R version?
Also R13 (sheet 3, at the U4A output) is 4.7k on the R board and 47k on the B board - is this a mistake? It is 47k in the BOM.
Because R17 (20k) is pulling the line up to +5V the signal would be to weak with 47k R13 - is this right?