bass wiring help

[kaboom]

i got a used '81 Ibanez Roadster just recently, and it looks like the wiring has been modified a bit. here are some pictures:

the controls. i believe the little switch is not original. knobs: two volume, one tone, the other controls the preamp i guess?


guts.


this is the little switch i'm unsure about. the tape says "center off." it's wired to the precision pickup, though i'm not sure exactly how. this is what i was hoping to get some insight about. there are four wires coming from the pickup, one goes to ground, the other three run to this switch. the pickup is off when the switch is centered (not sure the purpose of this), and one side sounds more full compared to the other, much more bassy. i'm guessing this was intended for series/parallel, just with the wrong kind of switch?


i don't know anything about preamps, but i assume that's what this is. it hooks up to a 9v battery, and it is attached to a pot that makes the signal louder. if you recognize it, i'd appreciate any info about this thing (make and model and such). i'll play around with it a little more to see if i like it the way it is, but i'm thinking i'd like to set it up more like the original rs924, with a hi/low shelf eq.

[McSpunckle]

Looking at that preamp, I'd be surprised if it wasn't the original one. It looks old... I don't know anything about date codes and such because I'm not a loser. But it's a dual OP-amp, which would work well for bass and treble controls, but since it only has one knob on the preamp, I dunno. Maybe a bass boost and a buffer? Or treble boost... or mid boost. Or some weird bass/treble boost where it's flat in the middle. I dunno.

The switch is almost certainly series/parallel. If it was a coil tap, it'd shut off half the P pickup, and it was a phase reversal it'd only do anything with the J pickup on, and it would make the sound super thin.

[kaboom]

Looking at that preamp, I'd be surprised if it wasn't the original one. It looks old... I don't know anything about date codes and such because I'm not a loser. But it's a dual OP-amp, which would work well for bass and treble controls, but since it only has one knob on the preamp, I dunno. Maybe a bass boost and a buffer? Or treble boost... or mid boost. Or some weird bass/treble boost where it's flat in the middle. I dunno.

The switch is almost certainly series/parallel. If it was a coil tap, it'd shut off half the P pickup, and it was a phase reversal it'd only do anything with the J pickup on, and it would make the sound super thin.

you are awesome, thanks!

i found some time to google, and it looks like someone else already did this detective work about the preamp: http://www.diystompboxes.com/smfforum/index.php?topic=46821.0;wap2
"I emailed EMG tech support... and the very pleasant and helpful tech informed me that it was and older version of their EXB, bass expander module, which is a bass/treble booster."
sounds about right to me. looking at emg's stuff, something like this might be a bit more useful if i decide to put the time and money into it: BTC Control. i will definitely replace the series/parallel switch, though. that thing is annoying.