Check the problem first. Tune the open string, then play the harmonic at the 12th fret and the fretted note at the 12th fret. If the fretted note is noticeably sharp or flat compared with the harmonic, the string isn't intonating well.
Common causes:
- Worn trebles. Frets and nails leave small dents in nylon. A dented string vibrates unevenly and plays out of tune in the upper positions.
- New strings not settled. Freshly installed nylon is still stretching. Give it a few days of retuning before judging intonation.
- Pressing too hard. Squeezing the string can push fretted notes sharp, especially high on the neck.
- Saddle or nut issues. If fresh strings still play sharp, a luthier can check the saddle and nut.
What to try:
- Replace the three trebles, or the full set if the basses are also worn.
- Retune often while they settle.
- Recheck the 12th-fret harmonic against the fretted note.
Our Classits Elite sets are built for this. They use the same wound basses and gauges as standard Classits, with treble nylon held to a closer tolerance to improve intonation up the neck and even out the three trebles. Choose ECM101 Medium or ECH102 High, both tie-end, in Classical Strings. Standard treble singles C-1ST, C-2ND and C-3RD are in Specialty Singles.