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Username: robbiec

Post Number: 1
Registered: 12-2007
Posted on Wednesday, December 05, 2007 - 8:06 am:   Edit Post

Is it possible to wire a 2 pickup bass with
-vol pot
-blender pot
-tone pot
-4 pole 6 position selector switch (pu 1, pu 2, pu 1+2 parallel, pu 1+2 parallel out-of-phase, pu 1+2 series, & pu 1+2 series out-of-phase)?
Advanced Member
Username: dfung60

Post Number: 285
Registered: 5-2002
Posted on Thursday, December 06, 2007 - 11:07 am:   Edit Post

You can probably get all this functionality on your instrument, but it's somewhat unlikely that you can do it with the controls you want. The problem is not that it can't be done, but that you would have to have some special parts like the switch made. Special parts would normally have to be ordered in quantities of thousands to get a factory to build them.

The functions are not that hard otherwise. You want a series/parallel switch which is a regular DPDT switch and a phase reversing switch on one pickup (doesn't matter which one), which is a regular SPDT switch.

The blend pot may be a problem as well. If you want to do series/parallel, then the pickups need to be passive pickups (e.g., they're just coils of wire and magnets), but passive pickups usually don't get along very well with a blend control, and especially in this layout. When you're in the "middle" of the blend range, you want to mix the full output of each pickup. If you try to make a blend pot by stacking a audio taper pot and a reverse audio taper pot on the same shaft, then when you have the knob physically in the middle, both pickups are at reduced level. In passive instruments, this will normally lead to both tone and output level loss; almost certainly not what you want. There are some custom pan pots (Stewart Macdonald sells one) that have special pots that have audio taper through half their rotation and full output level through the other half that would do what you want. The Stew-Mac part actually has separate outputs for each of the pickups, so it would work with your series/parallel switching; if the blend pot combines the two signals to a mono output, that wouldn't work. The alternative to having to find this specialized part would be to have individual volumes for each pickup. Separate indiv volume pots don't have the loss problem that a blend pot would.

The master volume and tone pots (whether passive or an active EQ circuit) would all be pretty normal. You may have noticed that I haven't said anything about a straight pickup selector switch. In the interest of keeping this too complicated, you're probably best off not having one and just using the blend pot or pickup volumes to select one pickup or the other. Note that when you're in series wiring, I don't think you can dial up just one pickup.

This wiring is sort of complicated, so I can see the attraction of having a big rotary switch that does this all. I'd make sure that it's worth having the series/parallel wiring vs. just parallel by hard wiring up an instrument and seeing whether the tonal difference is worth it. You can get pull pots that have the DPDT switching you need for series/parallel, so perhaps you would wire this up with parallel in the "down" position and series wiring in the "up" position. When the pot's not pulled it will act pretty much like a regular bass with the extra variations when you pull the pot up.

David Fung
Username: robbiec

Post Number: 2
Registered: 12-2007
Posted on Monday, December 10, 2007 - 9:57 am:   Edit Post

Thanks, David, for your knowlegable response. Let me digest this, look at the StewMac part, and I'll post a follow up.

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