There seems to be a lack of experience and opinion on TB as to what Bartolini pickups sound like in series and in parallel, lots of "in theory series will sound..." but no firm user experience so I thought I'd have a go at writing up my thoughts after experimenting with a set of Bart soap bar CBC pickups in my home build 5 string.
Just so you know the basic tone of the bass in question it has these specs:
-Ash body, made from planks of dense ash
-34' - 24 fret Maple neck with rose wood fretboard
-a pair of barolini BD5-CBC double coil soapbar pickups in 60's jazz bass positions.
- East U-retro % knob deluxe preamp
- Pretty high mass bridge from a yamaha BB605 bass.
-Strung with D'Addario Medium Lights.
After making this bass I was pretty happy with the big fat sound the Bartolini pickups produce in their "default" series wiring but after a week of playing it I was longing for more top end, here's my go at describing the tone of these pickups.
Overall - a very broad punchy tone, nicely rounded with a bit of low mid growl, you can hear it but it's quite hidden under the thickness of the pickups, the top end is rounded and has no shine or growl, nice but very low compared to the bass and mids.
Neck pickup: Warm and wide, think Pbass hollow grind and them boost the lows in a warm pillowy way, great warm full sound, no top end but beautiful fullness that begs to be played smoothly and it has a slight spank when slapped.
Bridge pickup: Punchy as heck! just a big punchy focused bridge pickup tone, not very honky at all, not Jaco, more full fat sound, great low B on this.
Both pickups blended equally: As you'd expect this is a blend of the two, some of the wider fullness of the neck and some of the punch of the bridge, good even response, a little more attack in this mode but not much, just a flatter, more even, more balanced tone (not that the others were somehow unbalanced)
I enjoyed playing the bass wired in series for a little while, it sits well in a band but in a big fat way, not hugely articulated like a jazz bass, more of a thick punch like a Pbass. So I replaced the strings and found the inherant tone of the pickups to be quite lacking in the top end, it can be coaxed out with a low mid cut and highs boosted but to me this didn't sound very natural so I wanted to try parallel wiring and here is what I think of this.
Overall: I was surprised how close to series parallel sounds, I think of it like this. The pickups have an inherent tone, a full bass response, a low mid presence which is punchy and has a dark growl to it and generally a subdued treble response, rounded is a good way of describing the tone. However parallel seems to have shifted the pickups emphasis slightly higher in the ranges, e.g. The lows remain the same punchy bass, the low mids are still there but slightly less than series and the mids seem to be voiced slightly higher now and the treble, though still rounded, is more audible. It's like someone took a rolling pin and flattened the fat series tone to be flatter over more frequencies. The bass still has a full bass tone, big and punchy but now has a more defined edge to the notes, nothing like as biting as a jazz but more than it did and the slap tone sounds more open now, less of a thick spank and more of a clang but again still with a fair amount of similar character to the sound, certainly not lacking punch and warmth.
Neck pickup: The pickup now have more of a noticeable tone difference between them, probably due to the flatter mids with less of a low mid dominance in their tones. The neck pickup has more of a growl now, slides zing a little more and you can make the pickup clack with a heavy attack whereas previously it would get louder now it gets more aggressive. the slap tone is like a jazz bass' neck pickup, hollow high and thick lows. The tone is still warm and rounded but has more open-ness to it, more flexible perhaps, the onboard preamp can get more out of it because it has more to work with.
Bridge pickup: This one surprised me, it still sounds very much like it's in series (it's not, I checked) it still has a LOT of punch but now with more bite to accompany that punch. The treble of both pickups is present but lower in prominance than the low mids so it won't sounds harsh unless cranking the top end at the amp/preamp. Slightly more articulation, still retains a killer B string and still holds its own against the neck pickup in output.
Both pickups: When panning you can feel the emphasis shift from wide fat bass at the neck to punchy articulate bass at the bridge but both blend well with a bit of jazz bass scoop coming through but bear in mind that's scoop when compared to two big pickups blended, by NO means thin. The blended tone does offer more highs and the high mid growl is apparent but like almost all the tones available it's still well balanced, great for a thick jazz bass tone, great for slap and the low B doesn't lack any focus compared to solo pickups, just a different mid emphasis.
In summary I'd say that these Barts definitely do have an inherent tone, a signature sound if you will, BUT, this tone can be emphasized or balanced by the chosen wiring.
If you like the big dark thick tone then wire Barts in Series, you'll get spades of low mids, a lot of bass and a rounded pleasantly smooth top end that is great fun to play and will sit well in mix in a punchy thick sort of a way.
If you crave a bit more definition then try parallel, the output difference isn't huge and the tonal shift is apparent but the bass doesn't sound thin, more detailed and perhaps more balanced tonally but still retaining the low mid punch of the Bartolini sound.
I personally prefer these pickups in parallel and although I've toyed with adding series/parallel switched for the pickups I can beef up the parallel with my preamp but I couldn't naturally shine up the series with it so I'm going to stick with parallel and pile on the bass when that series fatness is required.
I hope this might be somehow helpful for anyone trying to decide how to wire their Bartolini humbuckers or if you're looking for more than "just" the big dark Bart tone.