Organ / Guitar duo with vocals.
Rock Duo Magma is a good play and appropriate for the style - one track - 6 minutes release rock has a drum solo right in the middle of it - exactly what I was expecting to find somewhere on this album.
I think the reference I would use for this band is late 60's early Jefferson Airplane mixed with Iron Butterfly mixed with the Doors due especially to the feature roll of the organ. You will not notice the lack of guitar or bass here. The drums really fill in the bottom end and keeps the 'band' rocking forward. The organ is very busy though not really flashy and does all the work effectively fleshing out the sound that one would expect requires 3 other instruments.
Reissued in 2003 I can recommend this easilly to fans of this style of music. It is quite good. 1975 was too late for this album to come out - so in 2004 you can imagine that it's audience reach is limited. But if you wanted some of this old sound - ala the bands I referenced - but also want 'new' music that you have not heard before (you have play your Iron Butterfly so much it's boring) Rock Duo Magma is a very good pick.