Dummy Coil + Series Wiring

[hunchiepunker]

Hello to all!
I have the following equipment, intentions, and issues. Could anyone offer any pointers on how to wire this up sensibly?

First the equipment:
- One P90-style pickup, with braided shielded wire encasing two internal wires - hot and ground.
- One RWRP "dummy-coil" with similar wire-out. (no magnets or poles, otherwise a standard P90 bobbin)
- Two 330k Rickenbacker potentiometers.
- One DPDT ON/ON mini toggle switch.
- One tone cap.
- One Mono 1/4" out.

(Both the pickup and dummy coil were made for me by Vintage Vibe Guitars, as a pair for eachother.)

Now, I intend to wire this as follows:
- Position One on the DPDT switch is just the P-up (to volume, tone, and out).
- Position Two on the DPDT switch is both the P-up and the coil together in SERIES (then on to vol and tone as before).

SO! This should be very easy, but I'm too green to this kind of work to make sense of the best practices. Currently, the guitar is wired with the dummy coil in PARALLEL (with a standard Gibson style switch) and I find that the sound is WAY TOO BRIGHT! Series should tame the beast a bit, I know. I've decided that a push-pull pot is not an option for me, and think that the DPDT switch is just the trick.

Any ideas?

[David Schwab]

Ideally, the dummy coil should have poles, but no magnet. You want the dummy coil to pickup noise, and poles help. If you add enough metal to the dummy coil, you can wind it less than the pickup coil. This helps the tone situation.

The easiest way to wire that switch is to hard wire the dummy coil in series with the pickup. At the point where the two connect to each other, attach a wire going to your switch. The other side of the switch will connect to the other wide of the dummy coil. Close the switch and the dummy is out of the circuit.

You only need a SPST switch.

Now you have to decide is the dummy is between the pickup and ground, or between the pickup and hot. I think I'd put it on the ground side of the pickup.

Also, just to nitpick... the dummy coil does have to be RWRP, all you need is to either flip it upside down, or wire it in reverse. Humbuckers don't need to be reverse wound.

Also it can't be RP (reverse polarity) since it has no magnets.

[Steve A.]

Ideally, the dummy coil should have poles, but no magnet. You want the dummy coil to pickup noise, and poles help. If you add enough metal to the dummy coil, you can wind it less than the pickup coil. This helps the tone situation.

The easiest way to wire that switch is to hard wire the dummy coil in series with the pickup. At the point where the two connect to each other, attach a wire going to your switch. The other side of the switch will connect to the other wide of the dummy coil. Close the switch and the dummy is out of the circuit.

You only need a SPST switch.

Now you have to decide is the dummy is between the pickup and ground, or between the pickup and hot. I think I'd put it on the ground side of the pickup. [Clip!]

I had wired up a dummy coil in one of my strats, with the coil inserted in series in the connection to ground. (I just pulled the wire from all of the signal returns and tone controls that would have been going to ground and ran it through the dummy coil.) My thinking on this was that it would somehow be more transparent on the ground side instead of the hot side.

Everything seemed to work great until I brought it to the "bar from hell" one night, with wiring going back to the previous millenium... The dummy coil worked great with the volume control turned up but would pick up hum when I turned the volume control down. When I thought about I realized that the volume control was not able to fully ground the signal, since the dummy coil was between the pot and ground.

I never did get around to rewiring that guitar, with the dummy coil on the HOT side to confirm that theory.

I forget how I wired my Les Paul Junior with the single P-90 and dummy coil- I think the coil was on the HOT side- but that guitar has worked okay at The Bar From Hell...

Speaking of which, here is a tune I recorded there last Sunday night. This has absolutely nothing to do with dummy coils but it was a lot of fun (I take the first guitar solo 3 minutes into the song- my friend Felix takes the second solo):

http://www.megaupload.com/?d=NJ4HTUXX


Getting back to the issue at hand, here is a link to the article on my LP Jr with the dummy coil:

http://www.blueguitar.org/new/articl..._revisited.pdf

Steve Ahola

[hunchiepunker]

I had wired up a dummy coil in one of my strats, with the coil inserted in series in the connection to ground. (I just pulled the wire from all of the signal returns and tone controls that would have been going to ground and ran it through the dummy coil.) My thinking on this was that it would somehow be more transparent on the ground side instead of the hot side.

Everything seemed to work great until I brought it to the "bar from hell" one night, with wiring going back to the previous millenium... The dummy coil worked great with the volume control turned up but would pick up hum when I turned the volume control down. When I thought about I realized that the volume control was not able to fully ground the signal, since the dummy coil was between the pot and ground.

I never did get around to rewiring that guitar, with the dummy coil on the HOT side to confirm that theory.

I forget how I wired my Les Paul Junior with the single P-90 and dummy coil- I think the coil was on the HOT side- but that guitar has worked okay at The Bar From Hell...

Speaking of which, here is a tune I recorded there last Sunday night. This has absolutely nothing to do with dummy coils but it was a lot of fun (I take the first guitar solo 3 minutes into the song- my friend Felix takes the second solo):

http://www.megaupload.com/?d=NJ4HTUXX


Getting back to the issue at hand, here is a link to the article on my LP Jr with the dummy coil:

http://www.blueguitar.org/new/articl..._revisited.pdf

Steve Ahola

Hey, it's Steve Aloha!

I was inspired by that article you wrote on the junior with the dummy coil when I underwent this project! Rad.

By now I've tried the wiring several ways. First I tried it per the other poster's recomendation below, but had no luck - perhaps I've been misunderstanding something (not unlikely). It sounded shrill, and there was a significant drop in volume when both coils were together.

I ran out and got a new switch, this time a DPDT ON/OFF/ON. Then I began to reconceive the project. "What am I really doing here?" It's really analogous to wiring up a humbucker with a coil tap switch... the project is much easier to understand that way. So now the switch goes: Coils together in series (like a humbucker), off, then the pickup by it-self (faux coil-tap). I DID need a DPDT switch to do this.

From THERE, after the switch, the signal goes to the volume and tone controls, so there are no volume problems with the coils coming together after any pots. I'm using these rad 330k pots i got from Rickenbacker, and I'm REALLY pleased with them. In concert with a 0.015 mf cap, and the unique pickup, I have a really useful collection of sounds. It sounds a bit like a like a woody jazz box when in series (the guitar is an SG), and a super clean P90 when used alone - plus the volume roll-off is very usable all along the path, and the tone control is killer.

Super stoked on these tones. Can't wait to run it live.

Thanks for the help, guys. S Aloha was helping me before I even started with this! Funny!

[David Schwab]

By now I've tried the wiring several ways. First I tried it per the other poster's recomendation below, but had no luck - perhaps I've been misunderstanding something (not unlikely). It sounded shrill, and there was a significant drop in volume when both coils were together.

They are out of phase?

[hunchiepunker]

They are out of phase?

Now they're in phase, the hum is bucked, and the sounds are good. Much exceed my expectations, actually.

Originally I felt a bit lost about the wiring. I tried your recommendations as best as I could follow using the parts at hand - I had a DPDT switch, but only used half of it... connected the hot of the pickup to the ground of the dummy, then brought the dummy hot to the other end of the switch. Switch to volume, tone and &tc. Weird sounds. Too many variables to test out that evening. I was frustrated.

Luckily I had a few extra parts laying around. So I made a new harness the next evening. I decided that the way to approach the wiring was to visualize the whole system as a "big humbucker" - where I wanted the option of tapping the "P90" coil (actually a Vintage Vibe Guitars Charlie Christian style PUP) in addition to having the coils together in series. This was much easier to research then doing a "Dummy Coil + Series Wiring" search on the web, becuase coil tapping is much more common than adding a dummy coil - though the same principals are involved.

So I found the following images and used them as rough guides for my wiring:

http://www.stewmac.com/freeinfo/pick...s/duncan-1.gif

http://www.stewmac.com/freeinfo/pick...s/duncan-2.gif

These are wiring guides provided by Stew Mac for a major pickup manufacutrer. I followed the diagram for "Coil-Cut/OFF/Humbucker switching and ran with it - knowing that I'd change the labeling for this application, but the principles are the same. (I'd call it: Charlie Christian Pickup/OFF/Pickup and dummy coil.)

The sound is amazing - partly because of the great pickup, partly because of the rad pots and cap, and partly because of the wiring. Last night I demoed the instrument in a rehersal, and found the sound to be a bit TOO detailed for live performance with that group (that group throws out a lot of frequencies which battle the guitar. A strat is better suited to cut through in that application). Great blooze instrument, too bad I don't play blooze! It'll be backup on stage and a go to for studio.

All in all, it's been fun and now I wanna keep tinkering!

[David Schwab]

All in all, it's been fun and now I wanna keep tinkering!

Tinkering is fun! I have fond memories of all the wacky things I used to do to my instruments. I had a Ric bass with 10 knobs and 12 switches!

[Steve A.]

Now they're in phase, the hum is bucked, and the sounds are good. Much exceed my expectations, actually...

[clip!]

The sound is amazing - partly because of the great pickup, partly because of the rad pots and cap, and partly because of the wiring. Last night I demoed the instrument in a rehersal, and found the sound to be a bit TOO detailed for live performance with that group (that group throws out a lot of frequencies which battle the guitar. A strat is better suited to cut through in that application). Great blooze instrument, too bad I don't play blooze! It'll be backup on stage and a go to for studio.

All in all, it's been fun and now I wanna keep tinkering!

Now that you mention it, the first time I hooked up the dummy coil it was out of phase but humcancelling- which seemed to contradict everything I had learned in the Donald Brosnac book (the edition I had did have some mistaken concepts about cancelling hum). It was easy enough to put the dummy coil in phase, either by reversing the wires or flipping the dummy coil over.

I had a question about your observations at your rehearsal- did they apply to the P-90 with the dummy coil switched out of the circuit, or to just when you were using the dummy coil?

I picked up a LP faded cherry double-cut with two P-90's that is just begging for a dummy coil to be mounted in the control compartment...

I was thinking of using some tricks from the Suhr system- like trim pots to bypass the dummy coil and to add some brightness to it. As on a typical Gibson the two P-90's are *not* a RWRP pair so a single dummy coil should work for both of them without having to do any fancy switching. (What I came up with before would require an SG/LP style selector switch with two sets of contacts- I believe that the switch on a double-neck SG is exactly what I need but I never could locate a source for one.)

Getting back to the trim pots on the Suhr, once you find settings that you like you can replace the trimmers with fixed resistors. By wiring up resistors and/or capacitors in parallel with your dummy coil, you should be able to fine tune the sound and humcancelling effect a bit.

Steve Ahola

P.S. Say hi to Pete from Vintage Vibes! I guess he moved up to Oregon...

[hunchiepunker]

Really interesting... wiring resistors and caps in parallel with the dummy coil... To what effect? Where exatcly? I've never heard about this.

So far as that experience with this instrument in a band context, I think that the issues I've been dealing with are due to the capacitor choice that I made for the tone pot... it's a 0.015 mufarad disk cap - no doubt very old - which I got from the grab-bag bin at axman here in the Twin Cities. Thirtyfive cents!

The cap adds a kind of resonant hump to the signal path, and can roll back exceptionally dark. I find this to be my favorite tone cap I've ever used, and in conjunction with the 330k pots, it shovels away just the right frequencies to make for a very detailed tone. Has a great voice.

Continuing on, the two coils together don't sound all that different from the CC pickup by itself. As you said in your JR article, the series wiring with the dummy coil seems to add a bit of natural compression to the signal, it's like the signal has a little bit of lag to it as it fights its way through the dummy coil. In that particular rehearsal space, 60 cycle is a HUGE problem, and so the response was to the "humbucking" setting on the switch.

So, yes, the sound is super detailed. The resonant hump made it hard to find the sweet spot in that particular set of music (lots of mid-range competition from other instruments), but was more than likely not a result of the series wiring with the dummy coil. I've since used the insturment in a few gigs with that same group, and have been very pleased - mostly using the humbucking position on the switch, but flip it across for a little more push and dynamics. They really sound very similar.