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T-40 Wiring Mod

J Posega

J Posega

Cat Dad and Dingwall Enthusiast
Inactive
Suspended
Jul 16, 2005
11,796
17,172
38
Portland, OR
#1
I'd like to mod my project T-40 to have a coil-selection switch, either one per pickup, or a master switch, along with the standard two volume, two tone, 3-way pickup selector. A fellow TB'er, walterw, told me this:

i don't have any visuals for you, but the idea is that the extra wire from each pickup that goes to its tone pot will instead now go to that mini-toggle, which will have had all its criss-crossed phase-reversing leads removed, and the pickup that was going to that mini-toggle will now go to the pickup's volume just like the other one.

the mini-toggle has two rows of three tabs; each row is separate from the other one. use one row to hook one pickup's extra wire to ground, and the other pickup's extra wire to that pickup's hot lead, when the mini-toggle is thrown.

that should leave on the opposite coils in the two pickups.
Click to expand...

Now, I'm getting better at reading diagrams, but I can't wrap my head around this idea on it's own, in text format. Here's the original wiring diagram:

T-60.gif


How do I go about performing this mod? I have red, green/black, white and a bare wire coming from the pickups. I'm looking at ditching the spin-a-split tone controls, and going for individual HB/SC switches (I'm not worried about which coil [North or South] it uses, I don't really care to select one or the other, just that I can switch them, but if you have a way without modding the pickups to 4-wire, I'm reading).

I have the 6-pole, 2-position switches from 2 different wiring harnesses; can I use those for coil-selectors, or should I go for something else? Can someone draw-up a diagram for this mod for me; I'd be eternally grateful.

Sorry for this being so long-winded. Thanks!
 
#3
MNAirHead said:
Before doing this mod.... take pix.

IF you drill your pickguard the value will be compromised.. depending on your color combo, these are commanding increasing in value.
Click to expand...

Thanks for the input, but this is very much a project bass... pieced together from the classifieds and eBay. It's a 4-piece natural body (which I'm going to stain) with not-so-great grain and a black pickguard that's permanently splotchy and cracked, along with a maple neck. I'm not willing to pay $20 per knob, and one pickup ring is missing 3/4 of the plastic. The only parts that are really minty are the tuners and the bridge, which looks like it was mounted, but never touched or adjusted.

I've invested about $200 into it for the parts, and plan on customizing this to be kind of my dream T-40 (somewhere down the line, maybe a third pickup in the middle). I already have a stock '81 that I plan on keeping... at least until they start selling for vintage-snob prices.
 
#5
ah, you posted a diagram!

take the red wires off the tone pots, and take all the wires off the two-position mini toggle.

the bridge pickup's wires will go straight to the bridge pickup volume just like the neck pickup is. (you may need to add extensions to the wires to get them long enough, that's OK as long as the joints are covered so they don't short on anything).

if you stop now, you'll have a normal two-humbucker bass with an extra switch that doesn't do anything.

pressing forward,

the red wire from each pickup will go to the 2-pos. mini-toggle, each to one of the two center lugs. add two wires at one end of the switch, one on each lug; send one wire to ground (the back of any pot) and send the other wire to the same place the pickup hooked next to it has its white wire is going (should be a tab on its volume pot).

now, throwing that mini-toggle one way will do nothing, but throwing it the other way will send one pickup's red wire to ground (splitting off one coil) and send the other pickup's red wire to its own white wire (splitting off the opposite coil). this should leave on one coil from each pickup to hum-cancel with each other when both pickups are on.
 
#8
Nighttrain1127 said:
What I have seen done before is switch the tone pots to push/pull pots and use them to switch between dual and single coil modes no drilling required and reversable to original if you keep the old pots.
Click to expand...

This is what I would do - I want to remove the entire wiring harness including switches and pots from mine so I can easily return it to stock later on. I want to put the coil taps on push/pulls and turn the useless phase switch into a more useful series/parallel switch.
 
#9
you're not going to get series/parallel out of t-40 pickups, as they only have 3 signal wires, hot, ground and coil-cut.

unless you mean one pickup in series with the other pickup, a likely recipe for a wall of mud IMO.

ditching the annoying auto-splitting tone pots seems obvious, as does ditching the equally annoying phase-reverse (is there ever a use for that sound on a bass?) and using the toggle as the coil splitter for both pickups.
 
#13
Excellent, thanks for the help. The diagram looks pretty simple to follow. Now to acquire parts! I saw that thread on the T-40 forum, but the guy who did all the mods said he still preferred the stock T-40 sound. We'll see what happens with mine.

Think I should stick with 250k, or go to 500k pots? What size capacitor would you guys recommend?
 
#14
TheEmptyCell said:
Excellent, thanks for the help. The diagram looks pretty simple to follow. Now to acquire parts! I saw that thread on the T-40 forum, but the guy who did all the mods said he still preferred the stock T-40 sound. We'll see what happens with mine.

Think I should stick with 250k, or go to 500k pots? What size capacitor would you guys recommend?
Click to expand...

I did mine with a 250k pot and a varitone. If I used a cap, I'd use a .047µF Xicon polypropylene. Or Sprague orange drop.

In a pinch, this one will do:

Invalid Link Removed
 
#16
Cool. Hope it works out well for you. I've got a T40 pups habit too - I just picked up 2 more blades. Are yours toasters or blades? The blades are wound hotter. They run at about 5k per coil while the toasters run at about 3k per coil. A blade wired in series, at 10k, is pretty evil sounding. You can get series with a 3 wire but it will be out of phase. Fun to play with but probably not very useful in a normal setting.
 

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