Quote Originally Posted by BillTodd View Post
Do you even need a magnet?

A magnet is required in the pick-up (the pick-up is actually a variable reluctance) since the strings are not magnetic (i.e. they don't produce a flux). However, to vibrate the string surely only requires a varying magnetic field which could be produced with just a coil and a suitable pole piece. The effect of your magnet is to produce a strongly biased field - I can't see how that helps to produce the drive you require.
Yes, I thought the same when i started out on this journey, but you do need a magnet (& believe me I've tried just about every permutation).

You can think of the magnet along the lines of DC biasing in electronics terms (best comparison I can make). The guitar strings aren't 'magnets' ...just ferrous material, so the sustainer coil can only pull on them (& release)....that is, the sustainer can't "push" the string away from the coil. By having a permanent magnet, you can then have a slight quiescent pull on the string & then when the AC guitar (drive) signal is added into the mix, you're effectively getting a pseudo pull/push effect (on one half of the AC signal the permanent magnet's quiescent 'grip' on the string is relenquished which is like a pseudo-push...& then the other half of the AC signal the permanent magnet is given a boost, forcing it to pull stronger than in its quiescent state) ...it's difficult to explain in the written word, but yes, you really do need a magnet.

The other option would be to apply a DC biasing current through the coils (ie dispense with the permanent magnet - just a pure solenoid) .....the problem with this method is it'd draw too much current....& power is scarce on a guitar (such guitar circuits normally being driven by 9V PP3s, which are only 500mAH at best)