Sandy Bull was one of my favorites of the '60s/'70s "folk" musicians, although his music was much, much more than your typical "folkie" thing. Playing a variety of stringed instruments (guitar, banjo, oud, pedal steel, etc), his music was informed by various international folk traditions, modal jazz, Indian ragas, classical, blues, gospel, psychedelia and even Chuck Berry! He sometimes had percussionists (such as Billy Higgins or Denis Charles) as well as his own system of live tape overdubs and rhythm-machines. Check out his early Vanguard albums for some early excursions into psychedelic world fusion!
Bull's 1963 debut, Fantasias For Guitar and Banjo, was ahead of its time with it's psychedelic side-long raga-inspired modal number with Ornette Coleman's drummer Billy Higgins ("Blend") and its adaptations of Renaissance composer William Byrd, plus Carl Orff's "Carmina Burana" and a couple of gospel-inspired numbers. The lengthy "Blend" was as certifiably classic as any recording ever made and predicted the trend of Western pop artists looking East (and to modal jazz) for influence. Here is that side-long masterpiece:
Here's his reading of Chuck Berry's "Memphis, Tennesssee", from Inventions: