Double neck wiring question

[Rock64]

I have a double neck with an acoustic on the top side. Well, it's a fake acoustic, but I have a piezo in the bridge. I'd experimented for a long time with two sets of wires hanging off the guitar into two separate destinations. Once I was happy with my arrangement I decided to wire it up to a stereo jack and use a TRS cable divided at the end.

Problem I'm having is that despite absolutely zero contact with each other, the exception being the ground, I'm getting a 90/10 bleed both ways from the guitars. This is happening in the guitar as I have tested the continuity of every piece of the chain and the crossover bleeding is inside the guitar. I test the stereo jack before soldering and it's 100% fine. As soon as I solder the leads I have bleed. I'm getting bleed across the A and B as well as both with the ground. All with the guitar standing by itself unplugged from anything, this shows up on the meter.

Is this an expected problem? Every post I read about creating a wiring for a double neck like this starts out nonchalantly with a stereo jack (Rick-o-sound) as if it's no big deal and then the discussion moves to what happens after that. I have the after part figured out. The problem is in the guitar. It's not 50/50 as it was when I bought it. They had a switch for A, B, or both. Having both made the signal level drop to 50/50. This is more like 90/10. It should be 100/0 - 0/100, but it refuses to be. It's electric bleed not acoustic either. I solved the acoustic bleed issues a long time ago.

Am I missing something? I feel like the problem is in the ground wiring. Somehow, the close proximity of all this at the jack is causing a problem? It seems impossible, but that's what seems to be happening. I have a DD on the electric and a bridge stick piezo on the other. This would normally cause a problem just in resistance values if summed together, but remember these two sets of wiring never cross paths before hitting gear buffers. Two totally discreet signal paths (The exception being the ground).

Is there a proper way of wiring this so this is not a problem? A capacitor?

 

[Mincer]

Welcome to the forum!
I would guess the setup here would be something close to a regular guitar with a piezo, right? I have a Brian Moore that has a piezo, and uses a Y (insert cable) which is stereo at one end, and 2 mono jacks at the other. The piezo goes through an RMC preamp, though, and there is no bleed from one signal to another. Is your piezo active? Are there any other controls on the guitar with the piezo? What diagram did you use?

 

[Rock64]

I didn't use any diagram. I simply took out the mono jack, replaced it with a stereo jack. Disconnected the 3 way switch as I control any A/B outside the guitar. I wired the piezo (passive) directly from the volume on the acoustic side straight past everything else to the ring lug. Then the electric (passive) past the switch directly to the tip. Common ground. The piezo is passive within the guitar but it hits an analog EQ before going into any other processors. Further testing reveals the electric is pushing it's way into the piezos signal despite being completely separate. Not so much the other way around. I do know the difference between the electric bleed and the acoustic resonance bleed which I am fine with and is not an issue. This is definitely electrical. Your Brian May description is pretty accurate minus the buffer, which consequently might the problem. The design of a piezo is different and I'm thinking that somehow the common ground which was not so common before is allowing the DD signal to overpower the piezo not through the lugs but through the ground. I suspect a buffer pre would isolate the two signals. This is why I thought maybe some kind of filter in line with one of the ground connectors might be enough to push back the intrusive signal. IDK

 

[Mincer]

Yes, usually piezos without a buffer + preamp combo doesn't blend well with a magnetic circuit. Whomakes the piezo that you are using? Maybe the trick would be to install the buffer in the guitar before those signals are blended at the jack.

 

[Rock64]

Judging how well it all performed before I actually wired it up, I think you're right. I really don't know who made it. I bought a few cheap things off ebay when I started experimenting with this project and most things did not work out. If I had to guess I would think Artec. I didn't think I was blending anything this way. And I change my statement about the electric punching into the acoustic. Its pretty much even Steven. They're both bleeding both ways. Very annoying, and very perplexing especially since I thought I had this all figured out. Also, this piezo seems to have a bad crystal on the high E. It just has an awful splat sound every time I pluck it with authority.

Anyways, I now find myself wondering what to do about it. There's really no room in the sound box for electronics. I suppose it doesn't have to be there. I have lotsa room in the control cavity. This is so silly. I've never heard of anything like this where an audio signal goes backwards through the ground and pollutes the whole flippin mess.

 

[Mincer]

It may be an impedance mismatch between the 2 signals, which I think a buffer and preamp is designed to rectify. I know people on this forum have tried to do projects like this before (I actually haven't) so maybe we can get some clarity by someone who has run into this before.

 

[GuitarDoc]

First of all, there is no signal going through the ground wire so all the grounds can be connected without any signal bleed. You say that the DD pup hot wire (black) is going directly to the tip of the jack (green is to ground, red + white soldered together and taped off), and that the piezo hot wire is going directly to the ring of the jack. With this wiring there cannot be any bleed through from one pup to the other. There has to be something else with the wiring that you're not telling us. Are you sure that the jack is a stereo jack? Some jacks, even though there are three lugs on them are still only mono..

 

[GuitarDoc]

Check something for me. Disconnect the piezo from the ring of the jack. Do you get a clean signal from the DD to the amp through one of the "Y" cords (label that cord as "tip")? And nothing through the other "Y" (label that cord "ring" so we don't get the two mixed up)?
Now, disconnect the DD from the tip of the jack and connect the piezo to the ring of the jack. Do you get a clean signal from the piezo through the other ("ring") "Y" and nothing through the first ("tip") "Y"?

 

[Rock64]

First of all, there is no signal going through the ground wire so all the grounds can be connected without any signal bleed. You say that the DD pup hot wire (black) is going directly to the tip of the jack (green is to ground, red + white soldered together and taped off), and that the piezo hot wire is going directly to the ring of the jack. With this wiring there cannot be any bleed through from one pup to the other. There has to be something else with the wiring that you're not telling us. Are you sure that the jack is a stereo jack? Some jacks, even though there are three lugs on them are still only mono..

First off thanks for helping out. Everyone. 1) The ground. I know there is always a common ground and that no signal should be present. However, the ground is the ONLY connection between the two sides. 2) The wiring you describe is exactly correct with the exception of the DD going to its post on the blade, through the pots and then off the volume lugs to the jack. I also agree there is no possible way to have bleed this way. Yet it exists. 3) I purchased a 4 pack of stereo jacks. I'm no expert but I know how to use a multi-meter and I have checked and double checked and triple checked and checked once more for this post just to make sure I'm not mistaken...the jacks for the proper continuity and I can say with 100% certainty these are stereo jacks with no problems in their signal isolation...before you solder the leads to their respective lugs that is. Once connected your all mixed up. I even swapped out the first one thinking my luck I got a bad jack. The second was checked and was fine. Until I soldered the leads. I also checked the first one once it was out of the guitar and you guessed it. Perfect.

Now keep in mind that I have been playing (testing) this guitar for a year with this setup and original wires with the exception of the piezo being run out of the guitar bypassing the guts and going directly to the destination it is intended and I know that works 100% issue free.

To answer your second post. I don't really need to disconnect the leads as each side has it's own volume and if you turn each down then you get a clear path for the remaining side. Also, the bleeds are found coming thru the opposing side. So if I have electric bleeding to acoustic, and turn down the acoustic then it stops. Well they both stop. This is true for the reverse too. It truly is like I have the 3 way still wired and both sides are summed up. Sort of. As I said, it's not 50/50. Its more like 90/10 10/90. I've also checked countless times the signal path down the trs cable and the splitter at the end and it is 100% properly routing and/or isolating things as it should be.

I even thought maybe the shielded wire going through the guitar from the acoustic side was compromised somewhere along the way so I took everything out and traced it and it is 100% undamaged and free and clear of any contacts. This is embarrassing as it is the most elementary thing you can do on a guitar of which I have over 2 dozen.

Edit: Just to satisfy my curiosity, I soldered the DD directly to the jack with now no way of turning the DD side off with out external gear. Nothing has changed. Still bleeding. It has to be the jack. What else could it be if not my original guess that the two types of pickups are just not going to work together even if only connected by ground without a buffer.

 

[beaubrummels]

I think you need a buffer on the piezo. My understanding is magnetic guitar pickups generate AC signal, so I expect there would be some kind of signal present on the ground (someone check me on that), and also piezo generates signal when there is stress on the crystal and generates the opposite signal when the stress is relieved, which also results in an AC signal, which I would expect produces some kind of signal on the ground side. Without a buffer or load, I think it might be possible to get a small amount of stray signal through the ground.

It sounds like you have the DD on a blade switch. What else is on that switch? What is the full wiring of the guitar?

Try separating the piezo and magnetic pickup grounds completely and see what changes.

 

[Rock64]

I think you need a buffer on the piezo. My understanding is magnetic guitar pickups generate AC signal, so I expect there would be some kind of signal present on the ground (someone check me on that), and also piezo generates signal when there is stress on the crystal and generates the opposite signal when the stress is relieved, which also results in an AC signal, which I would expect produces some kind of signal on the ground side. Without a buffer or load, I think it might be possible to get a small amount of stray signal through the ground.

It sounds like you have the DD on a blade switch. What else is on that switch? What is the full wiring of the guitar?

Try separating the piezo and magnetic pickup grounds completely and see what changes.

I think I need a buffer too. Its a SSH combo original wiring from manufacturer. The last test bypassed that completely anyways. I'd love to separate the grounds but the whole idea was to get both sides traveling down the one cord. Before I wired this up the two sides were completely separate except for touching base to common ground in my processing gear. By that time the buffers abound.

This is the kookiest thing. I have to laugh cuz I always seem to get the stupidest problems when I think I'm doing what anyone else would do only to find out I'm the only one bothering to even try it. My whole life (I'm old) I've walked into guitar stores or repair shops only to see the dude at the counter roll his eyes when he sees me walk in cuz he knows I'm gonna ask some moronic question about some ridiculous idea.

This reminds me of a midi controller I had that was powering up on its own. It wasn't until I sent a picture of how it was hooked up to the manufacturer that I learned that what was happening was the power was back-washing into the midi out and powering the unit. I played out with it this way. The manufacturer said it might be working now but eventually this arrangement would burnout the board. I was essentially powering the sink with the sewer system, and here I am again. Only I could get the sound I want with it going backwards through the ground. Shakes head.

Ok with that being said, can I get away with a capacitor or diode or some type of check valve to block the interaction or do I have to use an amp? Would a blackout work or is that overkill?

 

[beaubrummels]

There was a thread on here just a couple weeks ago about buffers for piezos and it had links to other resources that showed how. I'd search for those. While I know about the need, I haven't had to make one myself.

 

[Rock64]

I think I found that thread. Fishman powerchip seems to be what everyone arrived at as a solution. That certainly sounds like a nice idea although I simply want separation, not mixing.

For what it's worth I tried to find something in my pile of electronics to test this theory of a buffer. I have a bunch of complicated piezo amp systems that never worked out for me so I settled on a circuit I actually made for an electric that was ready to go with leads and no jacks. I placed it on the piezo side and tested it. It was still bleeding over. I switched it to the electric side and the bleed stopped from piezo to magnetic. Interesting thing is the sound of the electric side improved immensely with my little circuit. I was having big fun there but it still pushed it's way into the acoustic.

This might not have worked 100% but it did work one way and proved to me that my signal path is not to blame.

 

[Mincer]

Well, that is a cool experiment, though. I wonder if you wired up 2 discrete jacks if you'd get bleed.

 

[Rock64]

Well, that is a cool experiment, though. I wonder if you wired up 2 discrete jacks if you'd get bleed.

I used to have two separate outs during the initial testing phase of this whole project with no connection to each other. Not even ground. Worked fine. Two discreet jacks would break the ground in the guitar and most likely solve the issue, but then I'd be running two whole cables out and that is the opposite of simplifying and just not on the table.

Edit: I decided to see what would happen if I went back to a magnetic pickup on the acoustic. After hooking it back up I tested for bleeding. Still bleeding. Am I making a monumental error in assuming you can have two guitars share a two lead cable with a common ground and not have them interact with each other?

 

[Mincer]

Well one might still need a buffer- does the acoustic you tried have an internal preamp?

 

[GuitarDoc]

To answer your second post. I don't really need to disconnect the leads as each side has it's own volume and if you turn each down then you get a clear path for the remaining side. Also, the bleeds are found coming thru the opposing side. So if I have electric bleeding to acoustic, and turn down the acoustic then it stops. Well they both stop. This is true for the reverse too. It truly is like I have the 3 way still wired and both sides are summed up. Sort of. As I said, it's not 50/50. Its more like 90/10 10/90. I've also checked countless times the signal path down the trs cable and the splitter at the end and it is 100% properly routing and/or isolating things as it should be.

I even thought maybe the shielded wire going through the guitar from the acoustic side was compromised somewhere along the way so I took everything out and traced it and it is 100% undamaged and free and clear of any contacts. This is embarrassing as it is the most elementary thing you can do on a guitar of which I have over 2 dozen.

Edit: Just to satisfy my curiosity, I soldered the DD directly to the jack with now no way of turning the DD side off with out external gear. Nothing has changed. Still bleeding. It has to be the jack. What else could it be if not my original guess that the two types of pickups are just not going to work together even if only connected by ground without a buffer.

Look, if you don't think you need to follow my advice to test where your problem is, then not only can I not help you, but you can't be helped.
The problem does not lie with the jack nor with the ground (per se), but with the way you have it wired.
I was trying to help you but since I can't have your guitar on my bench to do the necessary testing, you need to do it.

 

[GuitarDoc]

I used to have two separate outs during the initial testing phase of this whole project with no connection to each other. Not even ground. Worked fine. Two discreet jacks would break the ground in the guitar and most likely solve the issue, but then I'd be running two whole cables out and that is the opposite of simplifying and just not on the table.

Two jacks will NOT break the ground and will NOT solve the problem since the jacks individually still need to be grounded (to a common ground).

Edit: I decided to see what would happen if I went back to a magnetic pickup on the acoustic. After hooking it back up I tested for bleeding. Still bleeding..

Obviously the problem isn't with the piezo but with your wiring. Don't you want to get your guitar fixed and working the way you want it to?
At least, send some clear pictures of your control cavity showing where all the wires are coming from, every connection and where they are going. You may have to move some wires out of the way to show all the connections.

Am I making a monumental error in assuming you can have two guitars share a two lead cable with a common ground and not have them interact with each other?

No. Absolutely not. I've had several guitars set up to have separate outputs for each pickup (or a stereo jack with a "Y" cable).
You can certainly have your guitar set up to do what you want, but you have to be humble enough to admit that maybe there is something wrong with your wiring/soldering and be willing to make some corrections. But we don't know what you did wrong yet. You need to give us some pictures or take our advice on how to test your guitar.

 

[Rock64]

Oh I'm sorry, I did not see the second page of this thread. I'm not trying to be difficult and maybe I'm not explaining things as clearly as I should but in one way or another I have tried all of these suggestions. Some of them many times over. My soldering iron is burning up.

Guitar Doc, when you had guitars with this arrangement were they passive or was there at least some type of buffering going on?

I have tried one at a time. I've tried directly routing the individual pickups to the jack itself with zero connections in between. I've checked wires for damage. The only thing that has made any positive difference is my 9v circuit on the electric side. That seems to block the acoustic from coming through but not the other way around. As for my wiring, I admit it is possible I got something crazy wrong but I've essentially taken the wiring out of the equation.

I'd ask a local guitar tech to make it work for me but we have none here.

With that being said, I will share some info I picked up in a different forum today. This might explain things.

This is because of the common ground?
No, It happens because of capacitively-coupled crosstalk between the two output wires inside the cable due to the very high-impedance environment.

Why then didn't they do this when the two sets of wires I used to have, hit the common ground of my gear?
Because they were physically separate wires, so the capacitive coupling was negligible. The common ground is completely irrelevant.

So I'm correct in assuming that this passive arrangement is not going to work as is?
Only if you use separate cables.

Using a cable with two individually screened cores would undoubtedly help, but I expect you'll either need physically separate outputs and two separate cables (as per your trial rig), or active buffering circuitry inside the guitar to convert from the high-impedance internal wiring to provide low impedance outputs.

 

[freefrog]

I think you need a buffer on the piezo. My understanding is magnetic guitar pickups generate AC signal, so I expect there would be some kind of signal present on the ground (someone check me on that), and also piezo generates signal when there is stress on the crystal and generates the opposite signal when the stress is relieved, which also results in an AC signal, which I would expect produces some kind of signal on the ground side. Without a buffer or load, I think it might be possible to get a small amount of stray signal through the ground.

I've spontaneously thought the same. I'm too busy to check empirically right now but I'll share my results if I find some time to do a test on this question.