Ovation is an American guitar manufacturer best known for making high-quality acoustic and electric-acoustic guitars. To adjust the neck of an acoustic guitar, you tighten or loosen the truss rod. Unlike solid-body electric guitars where you adjust the truss rod at the top, you adjust the truss rod of an acoustic guitar from the bottom. Neck adjustments are necessary to increase or decrease the distance between the strings and the neck. You also adjust the neck to compensate for heavier and lighter gauge strings.
Test the intonation of the guitar. This is an indication of how much adjustment you should make. Plug your Ovation guitar into a tuner if you have an electric-acoustic model, or place a microphone tuner within range if your guitar doesn't have a pickup. Tune the bottom E string to the tuner, then play the same string at the 12th fret. If the intonation of the guitar is correct, the tuner should give an identical reading. If the intonation is out, the tuner will give a flat or sharp reading. Make a note of whether the intonation is sharp, correct or flat.
Loosen the strings so that you can get your hand inside the sound hole. Use a string winder to save time. You don't need to remove the strings, unless you plan to replace them.
Locate the truss rod adjustment nut. This is typically positioned on the inside of the guitar's heel. The heel is the joint where the neck meets the body. Feel inside the sound hole underneath the top frets to find it. Use your Ovation truss rod key to tighten or loosen the truss rod and thus, the neck. Tighten the nut clockwise to pull the neck straight. This will correct a bowed neck. A bow will cause your intonation to be sharp. Loosen the truss rod counter-clockwise to relieve the truss rod, so that the neck moves backwards. This will correct a warped neck. A warp will cause your intonation to be flat. The pickups on Ovation's electric-acoustic guitars are typically located inside the sound hole, so be careful when reaching in.
Tighten your strings and tune them using the tuner. Check the intonation again by playing the 12th fret of the bottom E string and comparing it to the pitch of the open string. Make small adjustments until your intonation is correct. Make further, smaller adjustments to refine the angle of the neck to suit your personal taste.
Test the tuning of the remaining strings. You can accurately adjust the neck relief using your bottom E string as a guide. When you have made your adjustments, however, it's smart to make sure the rest of the strings have correct intonation.
Use insulation tape to fix the adjustment key to the inside of the guitar. This way it's always where you need it. On guitars without a soundhole, adjust the truss rod from the top. Unscrew the truss rod cover to access to rod.
Make only small adjustments to the truss rod. Tightening or loosening it too much can damage the neck.