feedback and advice sought re: my wiring project [teardrop]

[Ro_S]

Hello,

I'm looking for feedback and advice, please, on the following proposed wiring design for my Alden teardrop guitar. I'm new to guitar wiring mods.

I hope this is the correct place to post this thread.

Proposed design :



(Note: I don't purport the above to be a proper wiring schematic or a circuit diagram. It's just a conceptual diagram, which I find helpful as an intermediate tool.)

Firstly, I'd be grateful for general feedback.

Secondly, more specifically, I'm unsure where a few elements woud be situated best in the circuit in my design:

i). There's the dual treble/bass tone controls which I have assigned to the P90 pickups, but maybe I should instead have them as master tone controls later on in the circuit?

ii). I have included a Fender Jaguar style 'strangle' type function on a toggle switch with two bass cut capacitor options. Is this feature best located before or after tone controls? And would it be better as a master function, rather than just on the P90s?    I'm thinking I should make it a master control so that it is after the series wiring option involving the middle pickup, to affect any 'mud' ?

iii). I've incorporated a fuzz effect. I've placed this last in the circuit, after all the tone controls; is that sensible?

iv).  what value pot is best suited to P90 pickups?  250k may be too dark?   I'm thinking 500k but with a 100k resistor across the lugs to make it 400k?   Thoughts?

thanks!

•  

[sumgai]

Ro_S,


That "diagram" was so... so.... I mean, my wife's eyes bugged out when this came up on my screen, and she was sitting across the room! I'm speechless, that's all I can say.


My answers, in order:

i) Master versus individual controls is a user preference, there's no universal "correct" answer to that one.

ii) Fender puts the so-called "strangle control" before any tone/volume controls. This might not necessarily be the ideal location, but that's what they do. However, your concern over any interaction with the tone controls is well-founded. I think you would be wise to lay everything out in such a way that you can freely experiment with the component values in the various tone control sections, before settling on your final parts selection.

iii) Unless you have a single-synapse reaction time, then I'd suggest you re-think this one. Installing any active effect on-board require two things - a battery, and a keen sense of where your switches/controls are, because when it comes time to make tonal changes, especially in "the heat of battle" (during a live performance), you've just exponentially increased your risk for a major screw-up. If you're gonna use this only for messing around, and possibly for recording, then fine, go ahead. But I can't count the number of times I've seen someone "reach" for a switch on his guitar, thinking he'd turn on a fuzz (or something else), and Whammo!, he's lost it. He misses a beat in the tune, the audience knows it, and his bandmates threaten to throw him out, if he ever lets that happen again. I trust I've made my point.

iv) Good luck with making a 500K pot into a 400K one by strapping a resistor across any of its terminals... ain't gonna happen. If you want a lower resistance to start with, then that's what you're gonna have to find/purchase. But I can say that in the case of Gibson guitars, they use a 300K pot for both volume and tone (treble cut). And your bass cut pot is gonna be much higher in value, so don't get any ideas of buying all the same thing, that ain't gonna happen either.

Hope that helps.





sumgai

[perfboardpatcher]

I like this conceptual diagram. Used in combination with a schematic it would help to explain that schematic.

As a guy who has built sustainers and installed in his guitars my first question would be: "Will it fit in?" And even when there is enough space, won't the controls get in the way? Some kind of 3D guitar space planner should come of handy. Or position the controls/jacks on top of the guitar. Or if you don't have them yet, use pieces of paper.

From 500k to 400k requires a 2.2M or 1.8M resistor in parallel with the pot. But I always would measure the potmeter first because of the tolerance of 20%(?). So yes, perhaps 600k to 400k could make some sense. But 500k to 400k?

Cheers,
Paul

[Ro_S]

Thanks for responses; I'll reply later.

In the meantime....

(paul -)

Re: control layout,  something I prepared earlier....



Here's a photo of the guitar:




It's a thinline semi-hollowed bodied.  Access is excellent because there is a sizeable cavity on the back like a Les Paul has.

Yes, I know there are a lot of controls and, ordinarily, I wouldn't seek to do that.  The Italian-made Vox Starsteam (c. 1967-68)  - picture below - was a large inspiration for my layout plan - and the built-in fuzz effect.   

[newey]

Ro_S-

Fit will be an issue. While the Vox may have been an inspiration, you don't have the cavity of the Vox. And I would not describe the control cavity on an LP as "sizeable". What you have planned won't fit in any LP cavity I've ever seen.

Of course, yours is a semi-hollow body so it might be possible to fit this all in. But I'd be drawing up templates to be sure. With a hollow body, you'll need to render the whole thing as a wiring harness- get that up and running before you start drilling holes in your guitar.

A couple of points:

First, a 4-way lever switch, as used in some Teles, is a 2-pole switch. What you are requiring this switch to do will require more poles- series/parallel requires 2 poles itself, and you'll need another pole (at least) to switch the middle in/out. This will probably require a Superswitch, available only as a 5-way switch, not as a 4-way.

Also, with the middle pickup engaged, you'll have 5 pots in the circuit. This will "load" the circuit quite a bit, and can be expected to dull the tone. Since you're using a "hot" Tele pickup in the middle, I can see why you'd want a separate volume control for that, so as to be able to match the outputs. But you might want to rethink having the separate tone for the middle- losing a pot would also simplify your fitment issues somewhat.

I think sumgai's right about the on-board effect as well. Those were tried (by Vox, mostly) back in the 1960's and never caught on, for the reason sg cites- a footswitch is much easier to actuate while playing live, and a stompbox can be powered by a wall wart, not just by a battery. That's why you can go into any music store and see dozens of stompboxes on display and not a single guitar with onboard effects.

As to your piezo, I don't think wiring 3 piezos in series will do anything more than one of them alone, other than perhaps making the guitar body more "alive", amplifying every little jiggle or knock you make to the body. Also, you will probably find that the piezo circuit will need a preamp to give a usable tone.

[ChristoMephisto]

That's a great layout for you idea.

Isn't the Strangle switch and the bass but knob doing the same thing except one is varible. Maybe one for the middle pup and the other for bridge and neck.

In the Vox Starstream the pickups go straight to the effects after the pup selector then to the master volume. Something to think about I guess. There isn't a lot out there about effect in guitars these days.

[Ro_S]

newey said:

Fit will be an issue. While the Vox may have been an inspiration, you don't have the cavity of the Vox. And I would not describe the control cavity on an LP as "sizeable". What you have planned won't fit in any LP cavity I've ever seen.
Of course, yours is a semi-hollow body so it might be possible to fit this all in.

Let me re-phrase what I said originally about the cavity.   When I referred to a Les Paul cavity size, I should actually have written aperture.   The rear access aperature and cavity cover are about the size as on a Les Paul.  

However,  the part of the guitar where all the controls and components are intended to be is entirely hollow.  So there is plenty of space and access.   The only part of the body which isn't hollow is a section between the bridge and rear strap lock, and is about 12cm across only.

But, yes, I should test it the final design for circuitry and controls all fit before I drill anything etc.

•  

[Ro_S]

Re: piezo -

newey said:

As to your piezo, I don't think wiring 3 piezos in series will do anything more than one of them alone, other than perhaps making the guitar body more "alive", amplifying every little jiggle or knock you make to the body. Also, you will probably find that the piezo circuit will need a preamp to give a usable tone.

Will a single piezo disc create enough volume ouput?   I thought two or three discs, but wired in series, would create a better output level and more representive pickup of the timbre/tonal balance?    If I place them below the high E string and/or the high E string side by the bridge block,  there should be very minimal complication of picking up my arm/hand knocking the body whilst playing, no?


I will being using an outboard acoustic preamp device (this one) in leiu of an onboard preamp.   I tried to show it on my conceptual diagram but it is only shown quite small.

•  

[ashcatlt]

Nov 29, 2015 8:45:19 GMT -5 newey said:

First, a 4-way lever switch, as used in some Teles, is a 2-pole switch. What you are requiring this switch to do will require more poles- series/parallel requires 2 poles itself, and you'll need another pole (at least) to switch the middle in/out. This will probably require a Superswitch, available only as a 5-way switch, not as a 4-way.

What I'm seeing him asking for is simple Baja wiring which is kind of what that switch is built for. You've got the B/N module and the M module. Each module ultimately has two wires coming out. It'll work fine.

Also, with the middle pickup engaged, you'll have 5 pots in the circuit. This will "load" the circuit quite a bit, and can be expected to dull the tone.

One of those pots is a bass cut, and won't have the same effect you'd expect it it was wired as a V or T. So now we're down to 4, which is like an LP. In parallel mode, the two Ts are basically redundant, but in series they will give a possibly interesting range of "Broadbucker" tones. Any or all of the tone pots could be no-loaded if we wanted.

Both of the highpass filters are going to depend (a lot) on the impedance of the load they're pushing. That will mean that the cutoffs will change as the 4-way is flipped, as other knobs are turned, etc. I do think that the strangle switch is redundant to the bass cut. You could use that switch to change the cap in the bass cut circuit, though.

I personally hate the idea of active electronics in a guitar, but in this case having a fixed and known load impedance could go a long way toward predictability and repeatability.

As to your piezo, I don't think wiring 3 piezos in series will do anything more than one of them alone...

I mean, I'm pretty sure they add (and cancel out of phase frequencies from different placements) pretty much the same as other voltage sources. What concerns me is that the capacitances in series are going to divide down and raise the cutoff of the inherent high-pass filter. If we actually want any bass out of the thing, it is going to have to hit a very hi-z load. It looks like it's intended to always go to some pedal, which might be fine as long as that pedal "expects" a piezo input.

And yeah, that resistor across the pot thing... Two resistances in parallel can never total any larger than the smaller of the two. 100K || 500K < 100K. So use a bigger resistor, but a pot is a three terminal device and your two terminal R can only really affect the resistance between two of those. It will change how big the pot "looks" when it's all the way up, and it'll change the taper, but it won't actually act like a 400K pot would. How much that matters is a real question, but...

You've already got (at least) a T pot sitting right next to the thing doing pretty much exactly what you want to accomplish with that resistor.

[JohnH]

This is a fun thread and I love those diagrams! I think they are a pretty good way to present the ideas, ahead of schematic and wiring diagrams.

A few observations:

With piezos, it looks like you are using disks, maybe taken from piezo buzzer elements? These work quite well, and I built one into a Strat (see schematics section). I mixed mine with the magnetic signal, using some on board electronics. But you are avoiding a whole lot of complication by not doing that, and that Behringer preamp looks like it will take care of the EQ. In case you get tempted though, we can talk more on that. People talk of piezos needing a high impedance preamp, and some do. But the disks actually need a reasonable load to roll off the sub-base. Each 20mm piezo disc is best thought of as about a 0.02uF capacitor which charges itself according to pressures that it picks up. I found that with one, it needed to feed into a load of about 150k for best results. You'll need to experiment with placement and also series/parallel. How much signal they pickup will depend on what you do. If you find yourself needing a bit more output, a very simple JFET circuit can buffer the signal and give a boost. But I suggest to start with how you are currently planning it.

With an on-board 'fuzz', tried that too. My son loved it when he was 13. So long as you can disengage it, why not? But there are some more watch-its:

The power should be engaged by inserting a jack into the guitar, using a stereo jack, with the ring terminal connected to battery negative, like in a stomp box. The power will therefore always be running, unless you have another switch to switch the power off. What does not work is to use the switch that engages the effect to also switch the battery power. There is too much of a nasty thump in the signal when you do that and there is no good simple way to supress this. You can supress the 'switch off' thump but not the 'switch on' thump. So that means another switch, which you should not touch unless the volume is set low, or the battery is always running when the guitar is plugged in. 

Feedback: When you put a high-gain circuit like a fuzz box inside a guitar, signals from the active output wiring can get picked up by the pickups and fed back, causing nasty screeches. This needs very careful shielding and separation of parts. Its not a problem with low gain buffers and boosters.

And as others have noted, it's way easier to engage an effect by stomping on it than by feeling for a switch, but dont let that stop you. The most famous guitar that I know of with an on board fuzz was Andy Summer's Telecaster (Police)

EDIT: On the series/parallel wiring to mix M with B and N: if you want independent volume controls for all that, I'd suggest treble bleed circuits on the volume pots. I'd suggest not to also have a Master volume, to reduce loading, unless you also add an active buffer (assuming you are having active circuits any way). Tone pots might benefit by being 'no-load' to help keep your treble in combined and series modes.

Another way to do that part of the switching, instead of a 4-way switch, is with two toggles, to engage the M circuit, N/B, both series or both parallel.

[newey]

I take ashcatlt's point about the 4-way switch- the reference to "bypass" threw me, but it is really just like one pickup alone.

If I place them below the high E string and/or the high E string side by the bridge block, there should be very minimal complication of picking up my arm/hand knocking the body whilst playing, no?

Understand that the piezo is not sensing string vibration in the way a mag pickup is doing. Wherever you mount it, it's sensing the vibrations in the body. You want density of materials around it- JohnH got good sounds out of one mounted to the trem block on a Strat, others have mounted them pressed between the neck and body, held on by a bolt-on neck. The commercially-made ones use the mass of the bridge, usually.

So, I'm not sure mounting them to a thin hollow-body top will produce good results. Under the bridge is probably your best bet.

As far as output, I missed the off-board pre-amp. Whether you get more output from multiple discs is something you can test in advance, if you already have the pre-amp. I frankly doubt you'll see much difference. And, you can always use the pre-amp to tweak the output a bit if that's the issue. Given that you're using separate output channels, you're not concerned about any volume differences with the piezo vs. mag pickups, as you can always "fix it in the mix" downstream of the guitar.

[perfboardpatcher]

Have you already tried to squeeze the last drop of tone out of the stock pickups? You could do some sound experiments with the stock pickups in series. (Bridge + middle in series in phase, neck + middle in series in phase, bridge + neck in series out of phase.)

It could be that these new combinations give you all the thin and fat sound variations you're after.

[Ro_S]

Nov 30, 2015 13:27:03 GMT -5 perfboardpatcher said:

Have you already tried to squeeze the last drop of tone out of the stock pickups? You could do some sound experiments with the stock pickups in series. (Bridge + middle in series in phase, neck + middle in series in phase, bridge + neck in series out of phase.)

It could be that these new combinations give you all the thin and fat sound variations you're after.

I'm using the guitar's stock Strat type pickups on another, Strat type guitar I have. Nothing wrong with the stock pickups - they're Entwistle vintage spec Strat pickups with Alnico pole pieces -  I'm just using them on a different guitar.

[Ro_S]

Many thanks for all the posts and responses so far.  I don't wish to intrude on the flow of input and discussion, so I've just intervened with clarification and extra info at certain points.  Please be assured that I'm reading everything that is contributed very carefully.   I'm very happy to take on board things to improve and correct my design ideas.  I'm sure I'll have some questions.  Thanks again, and keep them coming.  

[Ro_S]

Hello again,

Many thanks for all the replies and contributions.

I'll address all the issues raised in separate points below.   I have some questions.




1). piezo discs


Re: preamp.  To clarify: there won't be any active on-board circuitry re: the piezo, so yes I will be using an outboard acoustic preamp pedal device.  

Re: quantity etc.   The ones I have I think are 20mm diamter, so they are on the smaller side.  That's why I proposed to use more than one.  I now plan to use two discs, and wire them in series.

Their specs are apparently:  Resonant Frequency: 6.0KHz (±0.5KHz).  Resonant Impedance: 200W.    Capacitance: 14,000pF (±30%
).

Re location: -

newey wrote:

Understand that the piezo is not sensing string vibration in the way a mag pickup is doing. Wherever you mount it, it's sensing the vibrations in the body. You want density of materials around it- JohnH got good sounds out of one mounted to the trem block on a Strat, others have mounted them pressed between the neck and body, held on by a bolt-on neck. The commercially-made ones use the mass of the bridge, usually.
So, I'm not sure mounting them to a thin hollow-body top will produce good results. Under the bridge is probably your best bet.

Thanks.

My intention is now to locate both of the two piezo discs vertically against the centre block, right by the bridge.  The centre blocks only extends part way; it runs from the tail end and finishes just after where the bridge is.


2). enough space ?


There was a concern about whether there was enough space to fit all the electronics into the guitar.   It's a thinline semi-hollowed bodied guitar and the area where all the controls and components are intended to be is entirely hollow.  And access is excellent because there's a rear cavity plate there.    
I'll test the final design for fit before I drill anything, though.


3). on-board active fuzz effect

Okay, there received several strong reactions against this idea.  Ha.

I should state that I have a number of electric guitars and this is the only one I propose to put any on-board active circuitry on.  It's just for fun.  I don't generally endorse the idea.  I also have a spare Fuzz Face I can use and am I big user of fuzz.

A secondary point, there are two benefits of putting a Fuzz Face circuit in a guitar.   First, it won't interact badly with a wah wah pedal (Fuzz Faces are notorious for this); the wah wah pedal can therefore be put first in an outboard pedal chain as a precursor to a pedal board.  Second, a buffer can also be placed first in a pedal board's chain; this would not otherwise be possible becuase a Fuzz Face ideally needs a high impedance signal straight from a guitar.


JohnH wrote:

When you put a high-gain circuit like a fuzz box inside a guitar, signals from the active output wiring can get picked up by the pickups and fed back, causing nasty screeches. This needs very careful shielding and separation of parts.

Noted.  I'll bear that in mind.   QUESTION: What manifestation of shielding/separation would you suggest ?

Noted about a stereo output jack to stop the battery running down when the guitar isn't being used.  (in fact already incorporated in my conbceptual diagram).

QUESTION: is there a way can stop the battery running down when playing the guitar with the fuzz effect not engaged?



4).  location in circuit of fuzz effect

QUESTION:  fuzz before or after the tonal controls?   thoughts?



5). location in circuit of dual treble/bass tone controls

QUESTION:  I currently have dual treble/bass controls just on the bridge/neck circuit,  but I'm contemplating making them master tone controls and getting rid of the middle pickup's tone control.  thoughts?



6.)  'strangle' high pass filter functions, and their locations in the circuit

ashcatlt wrote: 

Both of the highpass filters are going to depend (a lot) on the impedance of the load they're pushing. That will mean that the cutoffs will change as the 4-way is flipped, as other knobs are turned, etc. I do think that the strangle switch is redundant to the bass cut. You could use that switch to change the cap in the bass cut circuit, though.

Noted, thanks!  I'll bear that in mind.



7.) four-way switch, and  in-series M with B/Neck functionality

There was a bit doubt about whether my 4-way blade switch will give the series function position I want, but that seems to be cleared up?   It will work, yeah?


JohnH wrote:

On the series/parallel wiring to mix M with B and N: if you want independent volume controls for all that, I'd suggest treble bleed circuits on the volume pots. I'd suggest not to also have a Master volume, to reduce loading, unless you also add an active buffer (assuming you are having active circuits any way). Tone pots might benefit by being 'no-load' to help keep your treble in combined and series modes.

Noted.


JohnH wrote:

Another way to do that part of the switching, instead of a 4-way switch, is with two toggles, to engage the M circuit, N/B, both series or both parallel.

Noted, but the guitar already has a stock blade style aperture and chrome surround, so I intend to add a blade switch of some kind for some purpose.



8). value of pots for P90 pickups


I keep getting different advice and reading different things about this.   The consensus seems to be 500k pots are frequently used and are fine?    Thoughts?    Maybe I'll try to find two 500k pots with high variance in value on the low side.




9). putting a resistor across lugs on a pot to reduce it resistance value


QUESTION:
I didn't understand the technicalities,  but a couple of people completely poo poo'd my plan to put a 100k resister across the lugs of 500k pot in an attempt to acheive a 400k pot.   I've read about this being done numerous times, so is this just incorrect?   I don't know what to think. What if one doesn't really use their volume knob; will the the darkening affect work in that respect?


I think that covers everything.  

THANKS!

[reTrEaD]

Hello, Ro_S

Dec 13, 2015 15:49:01 GMT -5 Ro_S said:

8). value of pots for P90 pickups


I keep getting different advice and reading different things about this.   The consensus seems to be 500k pots are frequently used and are fine?    Thoughts?    Maybe I'll try to find two 500k pots with high variance in value on the low side.

Sorting pots for small difference in value seems overkill to me. I'd suggest using 500k for both volume and tone on a P-90. If you find the high frequencies to be a little harsh, use a resistor in parallel with either your volume or tone (experiment with decreasing values until you find a value that takes the edge off).

Dec 13, 2015 15:49:01 GMT -5 Ro_S said:

9). putting a resistor across lugs on a pot to reduce it resistance value


QUESTION:
I didn't understand the technicalities,  but a couple of people completely poo poo'd my plan to put a 100k resister across the lugs of 500k pot in an attempt to acheive a 400k pot.   I've read about this being done numerous times, so is this just incorrect?   I don't know what to think. What if one doesn't really use their volume knob; will the the darkening affect work in that respect?

Multifaceted question. I'll take this in separate sections.

1 - Your math doesn't work. Resistance adds in series but it doesn't subtract in parallel. You have to add the reciprocals then take the reciprocal of the result. For instance:
1 / [(1 / R1)+(1 / R2)] = R total

or you can take the product over the sum...
(R1 / R2) / (R1 + R2)

For the 500k and 100k values you cited:
(500k x 100k) / (500k + 100k) = 83.33k

2  -  400k on one pot probably won't sound all that much different than 500k but going below 100k sure will!

3 - The basic concept of using a parallel resistor to decrease the resistance value of the pot is valid.

4 - The "darkening" is caused by loading the pickup. Lower resistance = more loading. You will still tame down the high frequency peak by adding parallel resistance even if you don't turn your volume control.

5 - If the 500k pots result in a tone that's a little brighter than anything you would ever use, I have an idea for a quicker way to determine the optimum loading. It involves a jumper between the CW lug and the wiper of a 500k linear pot that would temporarily replace your volume control.  But we'll burn that bridge when we get to it. 

[Ro_S]

Hello,

I'm bringing back this old thread of mine as I'm posting now about my revised plan for the same modification project.   This relates to a teardrop-shaped hollow-bodied electric guitar I have.  

I had, in the interim period, been planning of instead using this same guitar for an exotic sitar-guitar project; but now I've reverted back to my earlier mod plans for this guitar!  So....

I've reviewed my earlier plan and re-reviewed the feedback I kindly received from forum members in this thread.

Here's my new, REVISED PLAN for this mod project . . .

PLEASE SEE DIAGRAM BELOW (my conceptual diagram - not a wiring diagram!)

    >> Feedback and thoughts etc invited, please <<

My commentary re: changes and new plan:

I've generally streamlined and rationalised the number of controls and features.

The replacement pickups remain the same:  two humbucker-sized P90s (bridge and neck pair), and a hot Tele neck style pickup in the middle position.  (I'm going for an Epiphone Casino type vibe mixed with a 60s Vox.)

The pickup selector switching will now have only a single control (a 5-way Strat style switch), instead of two switches and two circuits as previously.

I've eliminated the separate volume and tone controls for the middle pickup.  They'll just be a single, global volume control.  

I'm proposing 500k pots for all of the volume and tone controls.

I've eliminated the Jaguar style high pass filter 'strangle' switch.  I felt it was overkill given the passive bass cut control, which now affects all three pickups.

I've eliminated the on-board fuzz effect.

I've retained the separate output for piezo capability. As before, this will rely on piezo transducer discs and an outboard acoustic pre-amp device.  

I've added a second piezo disc circuit to blend in with the magnetic pickups.  This is just an experimental bonus thing, really.  I've incorporated a switch to deactivate this function and so that the blender pot - which adds the amount of piezo mixed into the magnetic pickups' sound - can essentially be used as a preset control.

Thanks!

[JohnH]

I like the diagram style! It does help to look at it when figuring out a scheme, ahead of the wiring details, and it goes into enough detail to consider the implications.

A couple of things:

The magnetic side all looks to be in the right order. If you want to use a 500k volume pot, I think you might do better with a larger value bass-cut pot such as 1M, to get better range, and be ready to experiment with the bass-cut cap value. GuitarFreak can help you with that choice since it can model your basic circuit.

You may have read what I did to get piezo discs to sound OK. You have two going out to a separate preamp, so I assume youll experiment with that before going firm. For the one being mixed with the magnetic, I think you will definitely need a bit of active circuitry to buffer piezo and magnetic and then mix them. They wont mix well together otherwise, since the magnetics are inductive and the piezo is basically like a capacitance (expect a dull honk!).

[Ro_S]

Jun 21, 2018 15:24:30 GMT -5 JohnH said:

I like the diagram style! It does help to look at it when figuring out a scheme, ahead of the wiring details, and it goes into enough detail to consider the implications.

A couple of things:

The magnetic side all looks to be in the right order. If you want to use a 500k volume pot, I think you might do better with a larger value bass-cut pot such as 1M, to get better range, and be ready to experiment with the bass-cut cap value. GuitarFreak can help you with that choice since it can model your basic circuit.

You may have read what I did to get piezo discs to sound OK. You have two going out to a separate preamp, so I assume youll experiment with that before going firm. For the one being mixed with the magnetic, I think you will definitely need a bit of active circuitry to buffer piezo and magnetic and then mix them. They wont mix well together otherwise, since the magnetics are inductive and the piezo is basically like a capacitance (expect a dull honk!).

Thanks.

Re: the piezo circuit that combines with the magnetic pickups' signal -

Point taken, but I don't want to get involved with any on-board active circuitry.  I appreciate it's not ideal, but I'll go with the passive circuit and see how it goes.  I've heard others, on youtube videos, using a passive circuit in the manner I propose and it sounds reasonable.  This is only an experimental feature, and the main piezo capability on this guitar is the other, entirely separate piezo circuit with its own output going to an external preamp I've acquired for such a purpose.   

On my diagram, I've labelled the mixing or introduction of the piezo circuit to the magnetic pickups' signal as a ''blender'' control.  
Question:  Do I wire this pot simply as one would a volume control and then wire it direct to the output jack?
(Like how the middle pickup is wired on ''nashville wiring'' method is employed on a Telecaster with an additional pickup?)   
And, if so, does that mean the two signal paths (magnetic and piezo) are essentially being wired in parallel?   Is that okay?   It doesn't seem ideal to the combined sound/output? 

thanks

[JohnH]

Its hard to know how to make the magnetic/piezo blend work well passively since I don't think its a good idea at all! But I know its an experiment so youll just need to try things. Id start with just connecting them together directly in parallel to find out what happens. Those piezo discs have a capacitance about the same as a tone capacitor (like 20nF), so expect the magnetic sound to be dulled right down. But you may get some piezo signal coming through on top to add highs. For a blender, you could try a 250k linear pot. Each end of it going to magnetic and piezo respectively and the wiper to the jack. If you have a dpdt switch, use it to disconnect the wiper and magnetic end, so that your main magnetic signal path is restored to normal. 

[Ro_S]

JohnH -

What's the importance of the (pot byass?) switch being DPDT?  I don't have one. Could I use Gibson style 3-way toggles switch be alright for this purpose instead?  Or I might have a spare push-pull pot?   What would happen if I didn't implement this switch at all?  What's the disadvantage?       

Re: blender pot wiring.    So, the magnetic signal hot wire would go to Lug 1; the piezo hot wire would go to Lug 3; and, the hot output from the pot would come from Lug 2 to the jack. 
Have I got that correct?

Would this extra pot in the circuit have a loading effect on the magnetic signal, darkening it?   I don't think I like that idea.   Is that why I need  switch and for the switch to be a DPDT?

thanks

[JohnH]

Jun 22, 2018 16:58:36 GMT -5 Ro_S said:

JohnH -

What's the importance of the (pot byass?) switch being DPDT?  I don't have one. Could I use Gibson style 3-way toggles switch be alright for this purpose instead?  Or I might have a spare push-pull pot?   What would happen if I didn't implement this switch at all?  What's the disadvantage?       

Re: blender pot wiring.    So, the magnetic signal hot wire would go to Lug 1; the piezo hot wire would go to Lug 3; and, the hot output from the pot would come from Lug 2 to the jack. 
Have I got that correct?

Would this extra pot in the circuit have a loading effect on the magnetic signal, darkening it?   I don't think I like that idea.   Is that why I need  switch and for the switch to be a DPDT?

thanks

DPDT gives you the ability to fully disconnect the piezo and its blender pot wiring, for normal use. But if you have a push/pull, that is a DPDT so you can use that.

The extra pot will add some loading, so yes that's why you'll want to switch it out fully, especially since its experimental and you don't want to mess with the normal mode.

[Ro_S]

Update -

Below is the latest version of my plan in diagramatic form for my teardrop partscaster mod project.

I've simplified the electric (magnetic) aspect of this hybrid guitar.   Pickups wise, I've eliminated the middle pickup so now it's just a pair of P90 pickups. Pickup selection is via just a traditional 3-way toggle switch.    

As suggested (see above posts), I've added a DPDT bypass switch in respect of the experimental piezo/magentic blender feature.

I've expanded the passive piezo aspect.  One of the discs will be affixed to an internal percussion shaker!  I haven't yet decided how to wire the piezo 5-way switch.  The piezo circuit still has it's own dedicated output jack, and will employ an external acoustic pre-amp. 

Note: the guitar body has great rear panel access. 

Any thoughts/feedback welcome.

[Ro_S]

Suggestions, please, for what pot values I should use for the (global) volume control and the two individual tone controls - for my project's humbucker-sized P90 pickups ?

I'm thinking maybe 500k for volume and 250k for the tones.  Or vice versa.   Thoughts?

The pickups' specs are: 8k ohms, 4 henries (bridge);  7.5k ohms, 3.7 henries (neck).  Ceramic magnets.

[newey]

I'm thinking maybe 500k for volume and 250k for the tones.

I think that sounds like a reasonable choice, but tastes may differ.

Or vice versa. Thoughts?

I think versa would be a vice.

(That's a joke, perhaps a lame one. The resistance to the circuit is the same either way, but the 250K tone pots may have a better "feel", that is , more incremental changes). Any difference will not be huge.

[Ro_S]

newey - 

Thanks.

Would 500k pots throughout be too bright in your view, for P90s?

[newey]

Would 500k pots throughout be too bright in your view, for P90s?

Not in my view, but then, I'm an acolyte at the Church of Bright.

Bear in mind, turn a 500K pot down to about 7-8 or so (depending on the pickups involved) and you'll be at the equivalent of a 250K pot. Brightness can always be dialed out if it's excessive, but it's tough to add it if it wasn't there to begin with.

[Ro_S]

newey - 

Yeah, I agree; I'd much prefer something to start off being too bright than too dark.  

Epiphone Casinos of the 1960s used pot values of entirely 500k, I gather, so I can't see 500k being a bad choice for my purposes.

Now that I no longer have any in series pickup combinations in my plan, perhaps the bass cut control is rather redundant? Especially if I were to go with 500k pots?

I could omit the bass cut control, and go with a traditional 2vol/2tone configurations, all 500k pots.  What do you think?  That would help tame the both pickups in parallel selector position from being too bright, as there would be a 4th 500k pot in play?

What taper types do you suggest for volume and treble cut pots?   I know the rule of thumb often read on the internet is audio/log for volume and linear for tone; but what taper type allows for the best control in respect of each control type in your and others' view?

thanks

[newey]

I know the rule of thumb often read on the internet is audio/log for volume and linear for tone; but what taper type allows for the best control in respect of each control type in your and others' view?

This is mostly a matter of personal preference; I go with the conventional wisdom. As far as adding the bass cut, there again, it's a matter of preference. It simplifies things to omit it, certainly, but it's not only useful for series settings. In parallel, you can back off the treble a bit with the regular treble cut control, and then cut the bottom a little bit as well with the bass cut, leaving a sort-of "mid gate" filter. But I've never personally built or owned a guitar with the bass cut control, so no personal experience on my end.

[Ro_S]

Below is my latest version of my plan for this mod project, represented in my 'conceptual diagram' format.

I'd appreciate people's thoughts and advice on the following aspects, please:

1). is the best place for the VOLUME control in the circuit before or after the piezo blender feature?

2). will the bass cut control work fine in its indicated place in the circuit?   If I place the piezo blender control between the bass cut control and the volume control, will the bass cut control still work properly?

3). will it be possible to implement the blower/direct through modes okay?
To be clear; I want this feature to default the bridge pickup, superseding the 3-way selector switch, and bypass ALL of the tone controls, including that pickup's treble cut tone knob, with the signal going direct through to just the volume control. And I want an additional and similar direct through mode option to be a pseudo cocked wah sound.   

4). is the varitone type control in the most suitable place in the circuit?

thanks

Here's a summary of my planned mods to accompany the diagram below: 

• two pickups.  humbucker-sized P90s.
  
• pickup selection via a traditional 3-way toggle switch.
• single, global volume control.
• independent/dedicated tone (treble cut) controls.
• bass cut control - a la  G&L 'PTB' scheme.  global.  (ideally a reverse taper 1meg pot, but I may use a 500k audio pot wired backwards.)
• some kind of varitone type control.  six-way, 2 pole rotary switch with a bypass position.  treble cuts and bass cuts.  
• an experimental feature that blends a piezo disc in with the magnetic pickups' signal.  with true bypass to eliminate it wholly from the circuit.  
• a 'blower' (or 'solo') mode.
• a pseudo cocked wah mode.
• 
  

click HERE to access a version of the image that can be enlarged

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