Adding a Second Magnet to a 1967 SF-1 Bisonic

[lungimsam]

Well, I am glad the Bisonic is a single coil because that is probly the best sounding pickup I have ever heard in a bass in the neck position. Ric Toaster is tied, just a touch brighter sounding.

 

[Mosthigh]

So I got the alnico Bisonic-cut magnets from Rick Turner Guitars. I popped out the original one - which was glued in, and inserted the 2 new ones (no glue, seems to stay in place for now). The result is very noticeable lower output volume but clearer and growlier sound. I haven't run through my amp setup yet, just headphones on an old Tascam, but there is definitely a difference.

It seems to me the original alnico is stronger, and adds a bit more 'puffiness', for lack of a better term, as well as volume. I'll put the original back in soon and see how it goes with the new one, but I'm liking it for now, despite the output drawback.

 

[lungimsam]

If you try just using one of the new alnico's alone, I wonder if it will sound the same as the original alnico did alone.
Is it possible using two is having some kind of magnetic cancellation causing the drop in output?

 

[Mosthigh]

I took one new magnet out and left one new one in. It's back to it's regular output volume, with perhaps a tad more clarity. I did check the polarity on the magnets with a compass and vs each other, and they're facing the correct way in the slot (as they're curved, it's not hard to figure out). As Jack experimented on a 2-pickup Starfire model, I wonder if the magnetic circuit on the single SF1 Bisonic is different. I also wonder what effect moving the horizontal pole pieces (?) over the magnet closer to it would have. I guess it's just trial and error, though I'm pretty slow at getting around to tinkering.

I did come across this post on TB about adding magnets to pu's:

"A stronger field does not automatically mean more signal/volume. Moving iron magnetic pickups (what we have in our basses the string is the moving iron) work by demagnetizing the magnet - changing the flux through the coil is what produces output, and you need a relatively weak magnet so it can be demagnetized easily and thus produce a decent amount of output. The reason we can get away with old style magnets (alnico was developed in the 1930's, and ceramic magnets are very weak things) is that they demagnetize relatively easily - that means decent output in our case, but in most other applications, they're "weak/not very useful" magnets."

So perhaps the new magnets haven't been demagnetized enough and together are oversaturating the output. Next step is to try the original with a new one. I may email Turner Guitars and see what they say.