Well, like most any headphone, I suspect the better you're acquainted with the headphone, the less time it takes to evaluate a new piece of gear in the chain.
I could hear noticeable differences immediately, and more subtle differences pretty quickly.
I'll throw my K1000 in the car.
Very Gay of me to notice Ric, but that Cherry really pops in front of those Green curtains. You have them stacked the same way I did too.
I hope you love 'em as much as I did.
That truly sucks.
I can tell you that this is a very special amp indeed. Had I known how good, I could have saved some time and purchases prior to now. It is easily the best amp I've heard for the K1000. Even besting my DIY Pass F5.