RD Artist Bass Wiring Question

[BlendedCat]

I have a 1977 RD Artist bass that lately has become my favorite.  While the bass is really heavy, I never realized the wide pallet it could provide.

The version I have has a single three-way mode switch.  Position toward neck activates the bright boost, Center off, position toward back activates the expand mode (bridge pickup only) and the compression mode (neck pickup only).  The pick up selector is used to operate either one or both modes by limiting the appropriate pickup.  In 1979 this became two toggle switches; one turned the bright mode on and off – the other turned the compression/expansion mode on or off.  The electronics and wiring remained the same for both as did the way you used the pick up selector to run both or limit one of the modes

I would like to expand my options to include a toggle switch (on/off) for the bright mode and some sort of toggle where in I could run either, both, or none of the compression/expansion modes allowing me to always run both pick ups.  Has anyone had any experience with this?  I can decipher simple passive wiring schematics but this is intimidating and way beyond my knowledge and abilities. I have attached a Jpeg of the schematic available at fly guitar in case someone is inclined to take a peek.    Any help that anyone here could give me would be deeply appreciated.

[BlendedCat]

I think I sourced an answer to my question locally.  In addition I just scored a complete RD harness off of Ebay so I will be able to try out the solutions without risking my original equipment. (provided off course is it in working order when I receive it). 

[Highlander]

I took the big switch out of mine (purchased new in '79) and just replaced them with a pair of miniature switches, re-located to the bottom of the scratch plate, which worked quite well, and the pup-selector to an LP guitar position...
My PCB became glitch and got junked in the 80's and if I ever get round to finish off a rebuild she will have just the neck pup and a single volume control... and she's been fretless, courtesy of Peter Cook, since the early eighties...

[Granny Gremlin]

 I understand that you might want to have both pups on but only one of them effected, but this option is diminishing returns on tone IMHO.  That said, if you really want it; best of luck.  From a quick glance at the schem it looks like it might be possible without  PCB hacking (if not I would discourage it more strongly - those old PCBs do not take to reworking very well) - I always figured it was a shared FX on/off, but it looks like comp and exp might be discretely triggered on that 3 way switch, via multiple poles.

Also, an idea re the 3 way FX switch - instead of replacing with 2 toggles (requires drilling at least 1 new hole in the body), consider replacing it with a single 4 way rotary switch (nothing, bright, fx, bright+fx) - like an EB varitone.  No new holes required.  A 2P4T would do it.  If you also break out the comp vs exp this idea starts to get messy from a usability perspective, however, and you'd probably be better off with a 2 way bright mode switch and a 3 way fx switch in such a case.

Anyway, it is not a bad idea to do something here as that FX toggle is the most unreliable part in the whole bass though, I recently tracked down an intermittent signal problem to the long-buhing output jack (not a standard jack!).  Mine is intermittently shorting tip to ring.  This is rather unexpected as it's a quality Switchcraft jack, but I guess the cord got yanked a few too many times or something - just ordered/received a replacement and few spares - lucky I was ordering parts for a bunch of other projects anyway.

[slinkp]

What does the expander circuit do / sound like?

[Granny Gremlin]

The opposite of compression: increases the dynamic range; the loudness difference between the loudest signal peaks to the lowest noises. I like putting it through a distortion pedal - the attack is very distorted (more distorted than no expander into the same pedal/settings) but you get some smoother sustain, if not as much of it (less sustain generally; compression will increase sustain, because the quietest bits become louder,  the tail of the sustain being quieter than the initial attack). I find this allows one to go into chordy riffage without getting too muddy - nice tight buzzsaw.  On slower songs I tend to blend in a touch of compressed neck so that there is more body and sustain between notes.