Noobish - Master volume and crossfade between pickups on guitar

[paolo]

Allright, my question isn't really stompbox related as it will actually be inside a guitar I'm building. But I guess a lot of you are competent in both fields as I've found quite a lot of info for pedal type stuff here.  I'll start by giving you a description of my projects and than ask my questions. 


So, my plan is to build it using two p90 pickups, than having controls like on a Les Paul, independent volume and tone control for each. Than, instead of having a pickup selector, put a crossfader instead ( http://en.wikipedia.org/wiki/Fade_(audio_engineering)#Crossfaders_and_Crossfading ) than having the mixed signal go into a master volume witch would also integrate a preamp on the same knob.... somehow.

Firstly, the crossfader is going to give me some trouble, but I'm pretty sure I've got most of it figured out. First off, the commercial made crossfaders are mostly all stereo, think of DJ mixers. So my plan is to put two mono fader side by side but having one inverted to the other. IE When on one side,  the neck fader is maxed and the bridge fader cuts the signal. On the other side, they are the opposite, the neck is muted and the bridge is maxed. That way, I could mix my pickups on the fly without having to worry too much about the output strength. So, basically my question is, what resistance should the faders have, 500k like the volume pots ? If you didn't understand my explanation, if took out of context would be, if I was to put a fader after my volume and tone pots, what should be it's value (for only one pickup) ?

Secondly, for my master volume knob, what would be the best suitable value for that one ? As for the preamp, I'll probably just use a push-pull knob to have it run trough the other circuit, shouldn't be much of a problem.

Thanks for you time and knowledge, Louis.

[LarsXI]

There are dual gang pots with regular guitar values (500k, etc.) which serve that same function. The problem I see, is that with both regular volume knobs and that, you may be loading(or something) your pickup signal too much resulting in crappy sound. Also, with it wired like that, your crossfader will essentially be just another two regular volume knobs that are dependent on one another. There could be cancellation due to the way passive electronics work, maybe. Also, with the other two volume knobs the crossfader could act wacky and not give the range you expect.

If I was taking this approach I would run both pickups through their volume/tone combination for standard sound dialing, and then run the signals from that through separate preamps/a stereo preamp. That way, the guitar signal would be buffered and you could use that with an actual stereo crossfader found in mixers. Because the signal would be buffered, you wouldn't have to sweat about the eccentric nature of passive electronics. Instead, you'd get a nice fade. Just make sure the fader resistance plays nice with your preamps and take it from there.

As far as master volume after that, I'm not completely sure how you would swing it. The stereo fader would be acting like the volumes for the two seperate signals already. At that point, I'd almost say use the volume on the amp or get a volume pedal if you really need to adjust it on the fly.

I'm actually not 100% confident about anything I'm talking about here, but I figured I'd throw it out there regardless.

Sounds like an interesting project, enjoy.

[Ben N]

The simplest thing you could do would be to use a 500k stereo balance pot, available from Stew Mac, as your cross-fader (advantage: at center detent, both pot elements are at max resistance, just like separate vol pots), then your preamp (something like the Tillman would do), then something like a 25=100k-audio for your master. Keep the preamp in line all the time to avoid loading problems from too many pots; instead of bypassing it with your push-pull, use that to bypass the source resistor (or if you are using an opamp design, to un-bypass the feedback resistor), so that you are going from unity or slightly higher gain up to a hefty boost. Voila! I've thought about doing this with my Dillion LP goldtop clone with P90s, but I don't want to put a preamp in anythng that hums and I don't see any other way around the loading. G'luck.