Request for two small steel rod-esque lathed part!

[BillTodd]

These coils will actually be sustainer coils. The intention being to keep the guitar strings sustaining as long as the player wants them to. It does this by tapping off the guitar's standard pickup output signal, amplifying it & feeding the signal into these coils...this creates a varying magnetic field...& the guitar strings are ferrous so react to the mahgnetic field.

Do you even need a magnet?

A magnet is required in the pick-up (the pick-up is actually a reluctance sensor) 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.

[HankMcSpank]

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)