Peter B,
I too own this wonderful sounding preamp. If you got yours through John (assembled), he burned it in before shipping. The only change in sound will only be noticeable if you are using new interconnects. If you got yours "as a kit" like mine, the first 12 hours is nothing compared to around 150 hours or so. I posted about this topic earlier in this forum. I've use a FryKleaner with mine, 2-3 days, full volume with 1 input from the FryKleaner and the output to the inverted output of the FryKleaner. This is also how John burn his "units". Bass will be more defined, faster attack, smoother highs and well focused vocals. Off-course, this is from "my" experience. It will only get better in time. If you have the means, try this preamp with a SET amp using single driver full range speaker (eg: Fostex) and play Norah Jones..........you can smell her breath........that good! Godspeed.