The Advancing Guitarist by Mick Goodrick

I'm intrigued about the 'Modal Vamps' concept which is not clearly defined.

The perfect cadence, the resolution from V (or even more powerfully, V7) to I or i, used in major keys and the harmonic and melodic minors, is so overwhelmingly powerful that if you even veer close to it, you are likely to overwhelm any "mode" you try to stick to.

Whatever you try to do, the normal "key based" major will take over. Therefore, to play in a "mode", you need to avoid any hint of the V-I resolution.

For many "modal" songs, that means simply hanging onto a single chord, a "Modal Vamp". To play in D Dorian mode, you'd hang around in Dm6 for a long, long time, with perhaps the occasional foray into G (major, not minor), while avoiding A and A7. For songs in G Mixolydian, a G or perhaps G7 I chord with the occasional F. For E Phrygian, E minor with F and perhaps G minor while avoiding B.

Thanks again for your quick reply Helgi !! :)

I haven't read that book.

Vamps are simply repeated figures, usually in the bass. Think of Brubeck's "Take Five" - that's a one-bar vamp that's constantly repeated. They usually have just two chords, sometimes three, sometimes just one (a classical basso ostinato could be considered a vamp)

As Helgi pointed out, a 'modal vamp' is simply one that doesn't use a dominant chord.

Thank you Tom!.
By the way and just for the record, Mick Goodrick is a Berklee's teacher and Pat Metheny was one of his students.In fact the book is dedicated to him.

a good way to make vamps is to pedal the tonic of whatever mode you want it to be as a bassnote over a 4 - 5 or 6 - 1 progression. For example using the notes of the C major scale if you wanted to make a Dm dorian vamp you could play D as a bassnote and then a F chord, then D as a bassnote again and a G chord. You could just make it a D F D G or 2 4 2 5 bassline if you wanted. The 5th G resolving to the 2nd D instead of the 1st C is key to making the Dm dorian sound.

Vamps create a sort of instant modal environment to solo over, if you wanted to turn the above vamp into a F lydian vamp you would play an F as the bassnote over the F-G progression.

Thank you all for the cool comments ! and now that they have moved this subject to this department, I sincerely recommend this book. It is really enlightning.
(If you're curious check out the many good reviews in Amazon).