T-40 Push/Pull wiring.

Joe.shaffer · #1 01-26-2010, 12:55 AM

Hey everybody, don't know if this should be here or repair, mods please move if it needs to be somewhere else.

I was wondering if anybody had any thoughts on how to mod a T-40 for push/pull on the tone pots to control switching the pickups to single coil mode. For those of you unfamiliar, the T-40 tone pots are set up once the go above a certain point on the tone control it changes the pickups from humbucking to single coil.

From what I can guess, it's impedance controlled. Looking at the wiring diagram tells me that it's just a basic 4 wire humbucker. It looks like pretty standard three post pots on the diagram too.

Thoughts?

**line6man** · #2 01-26-2010, 07:13 AM

Quote:

Originally Posted by Joe.shaffer

From what I can guess, it's impedance controlled.

That doesn't make any sense.

The switching from humbucker to single coil is done by shorting out one coil if the pickup is wired for series operation, or removing one coil from the circuit if the pickup is wired for parallel operation.
You need a switch of some sort to do this.

Stealth · #3 01-26-2010, 07:54 AM

I believe Joe is right on this one, the S/HC action is impedance controlled because in each humbucker, one of the coils connects to the tone pot in such a way that sweeping gradually shunts one of the coils to the ground, effectively muting that coil and leaving the other one active.

http://natcade.tripod.com/schems/Peavey/t-40_t-60.gif <= Lookie here for a schematic.

Now, apparently, past a certain threshold (I think it's 70% of the linear sweep) we can consider that the hum-bucking effect kicked it. Trouble is, I haven't a clue how to wire a push/pull like that.

**line6man** · #4 01-26-2010, 07:57 AM

Quote:

Originally Posted by Stealth

I believe Joe is right on this one, the S/HC action is impedance controlled because in each humbucker, one of the coils connects to the tone pot in such a way that sweeping gradually shunts one of the coils to the ground, effectively muting that coil and leaving the other one active.

http://natcade.tripod.com/schems/Peavey/t-40_t-60.gif <= Lookie here for a schematic.

Now, apparently, past a certain threshold (I think it's 70% of the linear sweep) we can consider that the hum-bucking effect kicked it. Trouble is, I haven't a clue how to wire a push/pull like that.

Ok, so apparently it's somewhat similar to the wiring for a Jazz bass with the pickups in series with separate volume controls for each pickup then.

I can't open your link.

Stealth · #5 01-26-2010, 08:06 AM

No idea why it won't open. Relinking: http://natcade.tripod.com/pages/peavey.html
Also, it's described in Hartley Peavey's The Ancient Order of the Mystic Magnetic Pickup: http://www.peavey.com/support/techno.../chapter_5.pdf

xaxxat · #6 01-26-2010, 12:07 PM

Too bad Peavey didn't set these pups up as a 4-wire. I converted one to a 4-wire and hooked it up to a 4-pole 6-throw rotary switch.

I can get:

North coil cut
South coil cut
Series - in phase
Series - out of phase
Parallel - in phase
Parallel - out of phase

Series - in phase is "high pressure". Peavey really missed it on that one. The out of phase options sound very early Chris Squire-ish.

It's not easy to do the conversion as these pups are epoxy potted and the wire at the soldering lugs can be really brittle. You stand the chance of messing the pup up if the wire breaks. I've got a couple of pups that I've stripped of epoxy and wire and will rewind one of these days. Peavey used a weird soldering lugs and I've got to figure out a better way to hook the leads up.

**TheEmptyCell** · #7 01-26-2010, 01:11 PM

I'll ask here before I make a separate thread, but is there any way to wire up the T-40 pickups as they are, with only three wires, so that a 3-way switch could select North coil/both/South coil? I don't require any out-of-phase sounds, and I'd like the option of utilizing the full range of the tone pot.

xaxxat · #8 01-26-2010, 01:52 PM

If I remember correctly, the positions I got with the 3-wire and a rotary switch were:

North cut
South cut
Parallel - in phase
Series - out of phase

The 3-wire is a p.i.a. to work with. You could wire it white - red for North cut. Black - red for South cut. There's not a lot a of tonal difference between North and South cut. Sometimes I think I can hear it, sometimes I can't.

Then I believe it goes white + black - red for parallel. That daggone tone pot screws everything up. It certainly confuses me. That's why I went with a 4-wire. Plus, it gets the tone pot back to being a tone pot and not a switch.

Then I believe it goes white - black for series - out of phase. I could be wrong - it's been awhile since I did this and I can't find my drawings. There's probably a way do what you want with a toggle switch. I found a rotary switch easier to work with.

Anyways, that's my experience with it. The pup that I converted ended up in an SX shortscale and not my T-40 so I could keep the T-40 original.

PS - here's a site that discusses some T-40 mods:

http://peaveyt40.forumotion.com/weir...-i-did-t42.htm

walterw · #9 01-26-2010, 07:08 PM

wow, could anything be nerdier than an entire forum just for the T-40?

i've modded a few of the t-40s (and the t-60 guitars) to be way more musical (and logical, IMO), by dumping that ridiculous tone pot splitting thing, losing the nearly as annoying phase-reverse switching, and making that switch a master coil-split.

it's not hard to do, doesn't require modding the pickups themselves, and finally lets you get the sounds you're missing, humbuckers at full brightness and single coils darkened with the tone pots.

the only big "trick" is to decide which coil from each pickup you want to stay on, which you can choose by sending that extra wire from each pickup to either ground or "hot" via the little toggle switch. the idea is to choose a coil from one pickup that's opposite magnetic polarity from the coil you choose for the other pickup, so that when split with both pickups on, it also hum-cancels like a jazz bass.

xaxxat · #10 01-26-2010, 07:51 PM

Quote:

Originally Posted by walterw

wow, could anything be nerdier than an entire forum just for the T-40?

i've modded a few of the t-40s (and the t-60 guitars) to be way more musical (and logical, IMO), by dumping that ridiculous tone pot splitting thing, losing the nearly as annoying phase-reverse switching, and making that switch a master coil-split.

it's not hard to do, doesn't require modding the pickups themselves, and finally lets you get the sounds you're missing, humbuckers at full brightness and single coils darkened with the tone pots.

the only big "trick" is to decide which coil from each pickup you want to stay on, which you can choose by sending that extra wire from each pickup to either ground or "hot" via the little toggle switch. the idea is to choose a coil from one pickup that's opposite magnetic polarity from the coil you choose for the other pickup, so that when split with both pickups on, it also hum-cancels like a jazz bass.

School me, brutha. I'd love to see how you do this. I think I popped a vein in my head when I tried to figure it out. It was simpler for me to do a 4-wire since the pup I have needed to be repaired anyways.