When I was still on Talkbass, *sniff sniff*, I spoke to John Kallas a couple of times about the 1966 Slab Precisions. He was of the opinion that there was absolutely nothing special about them in terms of circuitry. This flies in the face of John Entwistle's claims, but makes a lot of sense. the Slab I've seen gut shots of has a black fiber bobbin and a grey fiber bobbin on the underside of each pickup half, so clearly they were thrown together from existing parts. I've seen the maple cap on the neck cited as a contributing factor as well, but again I find that hard to believe.
My personal stance is that the players, the strings and the amps changed just as the Slabs appeared. The two major players were Ace Kefford and John Entwistle, and both used Rotosound rounds and cranked the treble. Could they have simply done the exact same thing with stock Precisions with the body contours? I initially hypothesized that Fender, struck with the challenge of making a 'Telecaster bass', used 1 M pots off the Jazzmaster production line to get more top end out of the pickups, but apparently this isn't the case either. Rather, Kefford and Entwistle were making new sonic territory by gunning the treble on tube amps with limited headroom, and the Slabs just happened to be the bass driving this ensemble. Both players were given a wider degree of musical freedom in their respective bands as well. It all comes together nicely...
To bolster my theory, take The Who's gig from the Isle of Wight, 1970. I've seen this cited as an example of how a stock Precision just lacked the bite and grind inherent in the Slab circuitry. Yet, we know that John was running a simple bi-amp setup. I wager that they only mic'd up the 'bass' half of his rig. There are times when Roger Daltrey stands close to John's rig and you can hear the more typical Leeds tone bleeding into the vocal mics, which again backs up my argument. I would need to find an audience bootleg of that gig to reinforce my view, but I wager that any P bass with John's low action and zero relief setup would get the same tone through that rig. The idea of overwound pickups and 'inherent distortion' is a myth!
I don't see Fender winding hotter pickups for a small run of corner-cut designed basses for the limey market. It doesn't make sense to reward us with such a bespoke product if it involves holding up the production line.
All of this is just my opinion, and I would like to hear what everyone else makes of the Slabs.
