If your harp is in tune in some keys but not others then the chances are your levers need regulated.
So, what is Lever regulation?
Regulation is the process of setting the levers and bridge pins on the harp so that the levers raise the pitch of the string by exactly one half-step when they are engaged. A half-step is achieved if the lever is pressing the string at the proper location and the bridge, which guides the string through the lever, is at the correct height to stretch the string and produce enough pressure on the lever fret (from Rees Harps)
Harp levers are properly regulated when there is exactly a half-step in pitch between being on and off e.g. if your F string is tuned exactly to F-natural and the lever is properly regulated then when the F lever is “on” the tone will be an exactly in tune F-sharp.
Over time however, a common problem is that levers come out of regulation, meaning that when they are engaged, they no longer give a true, ‘in-tune’ half-step. Fortunately, most lever harps can be regulated, and minor regulation adjustments can be easily done by harp owners.
To see if you need to regulate your harp:
Tune each string precisely with the lever off.
Then, engage the lever and check with an electronic tuner to see if it is still in tune. If it isn’t, you will need to regulate it
When doing minor lever regulation there are two ways to alter the pitch of the note: raising or lowering the bridge or adjusting the lever itself utilising the slots on the lever. For a major regulation, the lever must be removed and reset. Even if you are only doing minor regulation the biggest thing to keep in mind is that a little goes a very long way.
1) Regulating with the bridge pins
You can regulate small discrepancies with the harp bridge pins. The bridge pins are threaded, so as you turn the bridge pin counterclockwise, the pin twists out from the neck. As you turn the pin clockwise it goes further into the neck.
If the levered note is flat, turn the bridge pin counter clockwise. This will raise the pitch of the levered note. Check the pitch and if it’s still flat, turn the bridge pin a little more.
If the levered note is sharp, turn the bridge pin clockwise to lower the pitch of the levered note.
You will need to turn the bridge pin a larger amount for the lower notes and smaller amount for the highest notes to make a difference in the pitch of the string.
2) Regulating with the Lever Slots
If there are bigger tuning inaccuracies, the lever may have to be moved. This is done by sliding the lever either up or down in the lever slots. To do this, loosen (but do not remove) the screws holding the lever so the lever can slide in the lever slots. Move the lever towards the bridge pin to lower the pitch, by creating a longer vibrating string length, or away from the bridge, which raises the pitch by creating a shorter vibrating length. Pinpoint the correct location with your chromatic tuner and tighten down the screws. This type of adjustment must be carefully done, as small movements make a fairly large change in the sharping, especially in the mid and upper range.
When you move the lever, be careful to keep it in line with, and exactly under, the string. Make sure you do not over-tighten the screw!
Good luck and remember a little goes a long way!!!