I was listening to this song;
Chord progression is something like this;
Am, E, F, C, Dm .(BTW His guitar is tuned half step down)
And almost all solos are in A minor or A harmonic minor scale.
I believe the chords above are in the key of Am (apart from E and not Em) So this song is in the key of Am.
But all of a sudden, there is a chord change at the 3.28 mark. He switches to C#m, and plays from the C#m pentatonic scale
C#m is not in the key A minor/harmonic minor but it sounds very good. Is this a common chord change trick when you want to switch to pentatonic scale in a harmonic minor song? Are there other examples of this? I'm impressed and want to formulize/generalize this.