I have some info to add to this thread, in case there is any lingering or future questions regarding the "bass boost" aka "suck switch" on a 1967-1970 SF Bass with Bisonic(s).
The bass that forum member Jules recently bought has the suck switch. It's a "late" 1967 SF1. Pup is in the neck. The bass, especially for its age, is in excellent to near mint condition. In fact when the seller told us the suck switch was perfectly functional and that the bass sounded amazing, just like a textbook Bisonic...to me that was a good sign, from 3,000 miles away, that nobody, no matter how many previous owners, was very serious about playing the bass for very long, ever. Basically the suck switch had not been removed OR started to act up at all, after 46 years...to me that was a sign the bass had not seen much use at all. And I was correct. just something to keep in mind.
back to the suck switch. In theory and function it is very similar to the "deep/hard" switch on the 70s/humbucker Guild basses. but at the same time, they are very different. they are not the same. Or if they are, the different pickups make their funcitons appear very different. The Deep/Hard switch on a humbucker Guild bass is not a bad thing (although they are just fine without the switch, as seen in a 90s reissue). I have finally learned how to dial in both deep and hard on my JS bass.
Jules' 67 works flawlessly. With the suck switch in the one position, it sounds very very very very close to the quintessential Bisonic sound. considering that, and the overall original condition of the bass, it will be a long time before we mess with it, unless it starts to act up.
With the switch in the other position though, it just sounds awful. no "bad function noises" as if there were a problem...its just that whatever it's doing was just a really bad idea. cuts the signal by what seems like 90 percent. it sounds nothing like the bisonic at all, with minimal volume.
I told Jules if we play with the switch enough it will probably start to get scratchy or cause some sort of problem with the one "Bisonic setting" and best just to leave it in the one position and not play with it. As long as it sounds the way it does now she is in no hurry to change anything. I do concede there may be a slight change in tone/sound or something if we disconnected the switch, but its 90 something (possibly a hundred) percent of the way there now and just sounds fantastic.
Jules' bass may need a setup or something down the road, if the time is right and it seems to make sense maybe she will have the switch disconnected at some point.
So I guess my point is when functioning properly, with the suck switch in the one position, if the bass has no other issues, it is essentially the textbook Bisonic, or very close. Probably more significant though, is in that scenario, its a good sign the bass may have spent most of its life in a case.
Jules' bass happens to document the suck switch under best case circumstances, but all in all I definitely agree with the general consensus, that to properly disconnect the suck switch can only be a good thing.
