The hurdy-gurdy story begins with the organistrum, though not much is known about its use in liturgical music of the time, although many commentators suggested a relation to organum. In early music circles, some controversy existed at one point over the mechanism, as one historical source illustrates a series of broad turning tangents in which all three strings were stropped in parallel. I remember a discussion with Dr Mary Remnant 30 years ago in which she dismissed this as being 'unmusical' (i.e. the idea of parallel 5ths and 8ves with no drone), and her reconstruction favoured the two drones & melody string played by pulling keys you're more likely to see in reconstructions these days. This is implied by the famous example at Santiago de Compostella (which can also be found in the Cast Courts in the V&A).

Here's what WIKI has to say:

http://en.wikipedia.org/wiki/Organistrum