I guess I should have said "pickup tinkerers"...

I have an old Ibanez Gio. I bought it from the used wall at Guitar Center probably 15 years ago. Since then I have had the whole thing rewired with better gauge wire, had better quality pots installed, and most recently had the cheap pickup switch replaced (and THAT was 5 years ago!). I probably have $250 into upgrading a $79 guitar, but this thing plays SO WELL and the humbuckers sounds so good that I just had to.

So on to now. I would like to get a single coil or a piezo, some kind of rail pickup, put in between the humbuckers. I want it wired directly to a volume control, then that volume control wired directly to the output jack bypassing any switching. That way I can blend in whatever amount of that out of phase single coil to whatever humbucker sound I have going on.

So maybe Billy with an electronics background (and of course anybody else) can chime in here. Can I wire it to the output jack that way without disturbing the signal flow of the humbuckers or causing any grounding problems?

In the picture the white arrows point to where I want the pickup and the volume control for it. It might take having some wood routed out on the body, but I don't care.

You can add a pickup and control without causing any grounding problems. A single coil pickup of any type will be susceptible to hum though. This can be minimal with something like Fender's low noise pickup. Or rail types are available in side by side humbucker versions that are as narrow as single coils. These also sound more like a single coil compared to traditional humbuckers (like you already have).

A piezo requires a very high impedance circuit. The existing circuitry would load it down too much.

Volume pots can be wired forward or reverse. If yours are wired forward, or you ever played a Gibson, you may have noticed that turning down one volume to zero, with two pickups selected, will kill the entire signal. So you don't want to wire the new added volume pot in the forward configuration or it will also kill the entire signal when rolled all the way back.

Forward volume pot wiring takes the pot output from the wiper (center terminal). Reverse wiring feeds the pickup into the wiper, and takes the output from the high side of the pot (an outer terminal). That's how you will want to wire the new volume pot. The Fender Jazz bass is an example that uses this configuration.

Wiring is simple. With pot viewed from the back with the three terminals on the left:

Pickup ground to lower pot terminal.
Pickup signal to middle pot terminal.
Pot lower terminal to output jack ground.
Pot upper terminal to output jack signal.

Anything you add to a passive circuit is going to affect things a bit. A 250K ohm audio taper pot might be a good starting choice. If there is a noticeable loss of highs with the 250K, a 500K ohm would be better. You may want a linear taper with the 500K ohm also.

The pot value and taper will affect the response (the feel) of the pot, how the pickup volume varies with the pot setting. In an ideal circuit, an audio taper volume pot will respond as one might expect; the volume will closely correspond to the pot setting. For the reverse wired volume pot in a passive circuit, the pot resistance and taper will both affect the response of the volume pot control.

Comparing audio and linear tapers, the audio taper will be more responsive at the higher volume settings. The linear taper will be less responsive at the higher settings, but more responsive at the lower volume settings. It can be a matter of preference.

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I think I am going to do this with an under bridge piezo. The first guitar I saw this on was a Duesenberg Sessionman that they made for Tom Bukovac and the tonal palate on that guitar is great. But as we all know, tone comes from the player more than the instrument and Tom is up near the top of the list. Still it would be fun to try this and I think the under bridge is the way to go for me. Everything in your reply was valuable! I may go as high as a 1m pot. I can always drop back to a 500k if I don't like it.

Now, every guitar I have had, mainly acoustics, that had an under bridge piezo were also active so I also have to think about where to put a 9v battery.

Eddie,

I wasn't aware they made Piezo Saddles for Tune-O-Matic Bridges but apparently they do. Here are 2 from Sweetwater, a 4mm and a 6mm.


https://www.sweetwater.com/store/detail/ghostLSR4N--graph-tech-ghost-loaded-saddles-for-resomax-nv-bridge-with-autolock-4mm-nickel


https://www.sweetwater.com/store/detail/ghostLSR6N--graph-tech-ghost-loaded-saddles-for-resomax-nv-bridge-with-autolock-6mm-nickel

Yes, Eddie, you can experiment with volume pots of different ohms. You also can get two-position push-pull tone pots and micro switches to devise more complex town switching arrangements.

RJ gave an excellent description of the possibilities.

You can buy pots and caps from many places. I get them from Digikey and CE Distribution. I have commercial accounts, but both places will sell to anyone retail.

9V batteries are customarily placed in routed-out spaces on the back of solid-body electric guitars and covered with a plastic or chrome plate. They are common on guitars with active pickups. That is a job for someone skilled in woodworking.

This guitar is wired, sort of what you are describing. The tone switch on the bottom is push-pull, and so is the volume control switch. You can also see the crap woodworking job I did on routing out for the Floyd Rose bridge. Perhaps one day, I will fix the mess.



Here you can see the micro switch I installed to add a second tone cap.

Just some ideas.

Billy

I hadn't considered that you might be willing to add a preamp for a piezo pickup. Was thinking all passive.

The Graph Tech preamp below will both buffer the piezo, and mix in the humbuckers and their controls. No modification necessary to the existing circuitry, just move the existing signal at the output jack to the preamp instead.

https://www.sweetwater.com/store/detail/AcousPhKit--graph-tech-acousti-phonic-kit-advanced

Interesting project.

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The graph-tech equipment and the Axon box are pretty cool stuff. But...a lot of guitar-playing skills would be needed to use it like it is being done in the video. Perhaps using this setup with a looper would be a fun toy. I can see this being useful in a buskin situation.

I would rather play keyboard parts on a keyboard and bass parts on a bass guitar.

I find that many things that seem excellent or valuable in the beginning don't turn out that way in the end. I built a custom amp using a Mesa Boogie Nomad 45 as a starting place. It is so complex and sensitive to operate that it is more work than I really want to deal with.

The idea of being able to get quality acoustic guitar sounds from my electric does appeal to me. I think I will go look around on youtube to see if there are any examples of this technology producing acoustic sounds that would be worth the effort to install.

Billy

I don't want it to mix in the humbuckers. I want to be able to leave the piezo off when I want to and blend it in to whatever humbucker combination I have set t any given time. Thus I want to wire the output of the piezo's volume pot straight to the output jack. Then, if I should choose to in the right situation (if there ever is one) I cold play just the piezo. This is the fun of thinking and speculating!! What to do? HOW to do? What will the result be?

This is how any field's nerds end up with a stack of napkins with never finished ideas! I've got probably a dozen songs worth of lyrics sitting in files on m computer. 4 or 5 wood projects, including how I'd build out a Nissan high top van for a travel vehicle. The bed that folds up so I can have a desk there during wake hours, the kind of cabinet hardware I need to keep drawers closed during travel, the solar power system, etc... And the odd thing is that I am by no means a draftsman, so they are sketches that mean nothing to anybody but me.

Here's a great example of how I tinker. I have a 2x12 closed back speaker cabinet. I saw somewhere a speaker cab that had one closed back 12" and one open back 12". I went and measured that back panel of that cabinet, pulled the back off to see how thick it was (1/2"), bought a piece of wood, cut out a port on the back of that wood behind one of the 12s, admired it for a few minutes, and never put it on the cabinet. I planned, I measured, I executed, but that was completion enough for me. All that remains on it is for me to pull the existing back off, lay it on the new one, mark where to drill the screw holes with an awl, and put it on. But in my mind, I am done just for having built it. That piece is sitting in my basement somewhere in a pile of wood.

I must have a dozen stories just like that.

Nobody ever accused me of being wound too tight. LOL!

The Graph Tech preamp will operate like that, but it does require that the preamp always be powered on, even if you're not using the piezo pickup.

Is that what you want to avoid?

If I understand, you want to add a piezo pickup and preamp, and then passively mix it into to existing humbucker circuitry?

I also design things that I never build. I have parts collected for several projects that are still sitting in storage boxes. The challenge is in working it all out, and often the only goal.

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You are close. I want to blend the output of what the guitar is right now but I want to blend it at the output jack so the piezo is completely separate from the humbuckers. Active or passive doesn't matter. I only even mentioned it because I wondered how hot the output of it will be. I have had acoustic guitars with the piezo under the bridge but every one of them had active electronics.

I guess I still don't understand what you mean by the piezo being completely separate from the humbuckers.

That Graph Tech preamp will do that. The humbuckers and piezo pickup are switch selectable. You can select humbuckers only, piezo only, or mixed. There is a trimpot on board, which I am guessing controls the balance between the piezo and passive pickups. There is also the external piezo volume pot to control the actual level, of course.

I am assuming you are not talking about separating the two into a stereo jack?

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This. Humbuckers blend like always. Piezo added as I choose. Run the piezo volume (no tone) pot straight to the output jack. I want the volume pot for the piezo to operate completely on it's own, so separate from the humbuckers. It won't run through the switch or have anything to do with the humbuckers.

For example, if I find a sound I like with neck on 10 and bridge on 4, I want to then have the option of turning up the piezo to blend it in and maybe smooth it out. So I would end up with 2v and 2t knobs for the humbuckers and a volume (only) just for the piezo. It just adds another layer of timbral options. It will look funny with a 5th knob, but who cares? And even when this is done, I may NEVER use that piezo, but it's the journey more than the destination with me.

Your drawing basically shows the functional operation of the Graph Tech preamp.

The only thing missing is the selector switch at the preamp output.

(just as a note, the humbucker selecter switch should be after the controls, not before)

If you are concerned with keeping the piezo signal pure, the preamp will do that. The preamp selector switch is a convenience that allows you to leave the controls at their settings and switch between pickups without having to re-adjust them. Without the switch, you would have to roll the volumes all the way back on the unused pickups, and reset them again when used.

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I have the GraphTech bridge and piezos in my Parkers.

Piezos alone on the solid guitar do not make it sound like a flat-top. The sound is thinner, more like an arch top.

My Digitech RP355 pedal has a nice acoustic simulation that I use when I want to sound like a flat top.

The Parkers are wired with a 3 way switch (mag/mag+piezo/piezo). There is a separate volume potentiometer for the mag and piezo pickups, so when I play both, I can use the piezo volume control to blend the piezo with the magnetic pickup tone, and get some nice tones that have the body of the mags with the twang of the piezo added.


Insights and incites by Notes ♫

What you are describing works with an additional passive pickup because all the pickups and controls are of similar impedance.

The piezo element itself cannot be mixed in with the humbuckes due the relatively low impedance of the humbucker circuitry (compared to the piezo element). As I mentioned, the humbucker circuit will load down the piezo element.

So a preamp or buffer is necessary. But if you try to mix the preamp output into the output jack through a volume control, you will now have the opposite problem. The preamp output is a very low impedance, and will load down the humbucker circuitry. In fact, it would practically kill the humbucker signal completely with the piezo volume at 10.

The Graph Tech preamp includes a two channel mixer, with the piezo signal on one channel, and the humbuckers on the other. Just like any mixer, each channel operates independantly of the others with no interaction.

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If my only option is using that kit I probably won't bother. This is now WAY over my head and would need a tech to do it, as well as me being cheap and not willing to spend $140 on the kit JUST to do something because I can. Been a great discussion though!