do you mean pickup output/gain on the amp or perceived volume when playing through the amp distorted?
I find that they seem to drive the preamp less because they sound in general less compressed than mass production pickups, but when playing with a band they cut through much better with more clarity, hence appear louder in the mix.
As Hunter and Dave_MC noted, I did not notice a volume drop as such with my B.K.P , but it changed the sound from a 'blocky' / blunt sounding stock pickup - to a more detailed presentation. If I had wanted a
perception of blunt power, the stock pickups did that. The only analogy that comes readily to mind, is the difference between listening to a 'Ghetto blaster' and a high quality home - Hi-Fi. The Ghetto blaster seems louder, as it is focused and lacking subtlety, but the home Hi-fi fills the room instead , with 3 dimensional detail.
I can only comment on B.K.P. vintage, but I buy those for the detail, the 'fine grain' . As Hunter also observed, this clearer separation of frequencies within the pickup, sounds more omni-present in the mix, as 'shards' of it's detail can be heard around and in between the other instruments.
They are a different creature though,
I can see what you mean, and why you asked - as a pair of Mules in my Les Paul Standard, are very different in presentation from the stock 498T and 490R that were in there. I think it is usually noted ( Twinfan's posts come to mind ) that with B.K.P , you have to work harder, the pickups want to be told what to do by the player, not homogenize the product of your phrasing.
Your observation being of course valid, but perhaps comparing oranges, to other oranges, instead of apples to oranges. :)
