Wiring a piezo pickup preamp system and a magnetic pickup with a 3 way switch

Hi guys, I'm working on a 6 strings CBG, and I'd like to install both a piezo and magnetic pickup; I don't know if it's possible, the idea is to use a 3 way switch to blend the magnetic and piezo, using them separately when I need: basically, position 1 is the magnetic pickup by itself, position 2 could be both magnetic and piezo, position 3 the piezo by itself.

I'd like to send the piezo through an EQ preamp system I've got on eBay (you can see it in the picture below), but I'm not sure about how the wiring works.

Any suggestions?

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Hi Matteo,

It is easy if you break it down into sections - the wiring of the piezo/magnetic pickup with a 3 way and then the preamp.

First part
Do you want passive volume or tone potentiometers added prior to the preamp? (note that a passive tone doesn't work on piezos). What kind of 3way switch do you have (telecaster type or les paul type)?
When looking at different diagrams just consider the piezo to be like any other pickup with a single + wire and a - wire. Places to look for ideas are here http://www.artecsound.com/wiring/wiring_book01.pdf, seymour duncan (though diagrams are often very complex for 4 wired pickups but still worth a look) http://www.seymourduncan.com/support/wiring-diagrams/
and Ted Crocker's diagrams (if the diagram has a disc piezo this can be substituted for a rod piezo) http://handmademusicclubhouse.com/photo/albums/wiring-diagrams-sche....

To make the rod piezo into a pickup with a + and - you cut about halfway along the length between the rod and the little silver jack plug. The outer wire braid can be teased off the inner plastic sleeve and twisted to form the - wire and if you carefully strip off the plastic inner sleeve you will find the + wire. These can then be added to your circuit (just check you will have enough length to get from the under bridge saddle piezo rod to the circuit, though in reality the preamp is for a large regular guitar so wire length is not normally a problem). Keep the other half with the little jackplug on as this will be used for the preamp input.

Variations - if rather than use a rod piezo you can wire in piezo discs instead and they will work fine with the preamp.
Rather than a 3 way as Wayfinder commented you can use a volume switch with a diode for each pickup so you can blend the signal from the two pickups (a blend pot can also be used but the signal ratio is fixed and offers less variation). The diodes are really cheap and the type I use are 1N5819 the concept for this I found from here http://www.strat-talk.com/forum/stratocaster-discussion-forum/13405...
The idea is that a volume pot acts as a signal divider sending the signal between ground and the live output. Once the pot is turned to zero the whole signal is lost to ground and you get no output. By adding a diode to the live output lug on the volume pot it acts like a one way "valve" to the signal separating the part of the circuit turned to zero from the rest.

So from the above once you have the circuit you want the diagram will end with the output jack. This is where you follow on with the preamp. I have used 4 of that kind of preamp and you need to be aware that once the battery runs out of power you lose the sound. I get around this by wiring the guitar circuit I want to a switchable 1/4 inch jack socket like these http://www.ebay.co.uk/itm/320690495233?_trksid=p2060353.m1438.l2649... they work by the jack plug lifting the wire bar from the connection on the other side (look at picture 2) without a jack plug the signal continues out the other set of lugs.

So if you decide you want the preamp inside the cigar box you now take the other half of the piezo rod cable (with the little jack plug attached) and tease the silver braid for the - and strip some of the inner sleeve to give you the + and wire it to the other side of the switchable jack (note the + wires link to the tip of a jack plug so solder these to the lug furthest from the jack opening) note wires from the guitar circuit go to the lugs with the arm over the top and preamp side wires to the short arms. The small jack fits into the small jackplug hole on the preamp module and the preamp module and battery/jack box have a lead that clips together.

Note that the preamp and box require a big hole for each so brace the box well or the 6 strings will bend the box. Also note the preamp will stick out due to the curve (meant for the curve of an acoustic guitar).

I am on my ipad so unable to add a photo (will do so later if needed) this should link to a preamp like yours in situ

And this is an old video (turn the volume up full as the camera mic sucked) showing piezo and magnetic pickups mixed with and without a preamp.

Also as Wayfinder suggested you can put the preamp in a separate box to use with all guitars

Once you have an idea of the guitar circuit you want just ask if you need further help.

David L

Thank you for your fast answers, you gave me few ideas that for sure will be useful for my CBGs.

Anyway, to answer to David: the 3-way switch I have is a Les Paul style (you can see it from eBay in this link: http://www.ebay.it/itm/271594846083?ssPageName=STRK:MEWNX:IT&_t...).

The links you provided me have been useful to get new ideas, expecially Ted Crocker's diagrams: there I've found some schematic plans about how my CBG has to work.

I did a new image, to better explain my original idea, just to know if that could work; I need the preamp just for the piezo.


I can see what you are trying to achieve, but the preamp is switched on by the insertion of a jack plug into the battery/jack socket part - they split the battery negative wire and use a stereo jack socket which has two sleeve terminals (so it has 3 contact points for stereo outputs ie left, right and a common ground). If a mono jack plug is inserted instead of a stereo plug the two sleeve contacts are connected giving a way to split the battery negative wire going to the common ground. This then acts as an on/off switch (it also means you drain the battery if you forget to remove the amp cable after playing).

For your preamp part of the circuit to work as you want you will need to add an on /off switch to connect the negative battery wire to the common ground.

If this isn't clear I can add a photo or diagram when I am on my desk top computer.

David L

As drawn here, it will work fine. The pre-amp appears to have a power on-off button, and if true, the comment from David L. regarding a switch, etc. is not needed.

One thing to note: when the 3 way toggle is in the middle position, the volume and tone controls for the humbucker will be bridged to the pre-amp. This likely will not result in the h-bucker volume affecting the pre-amp controls. But the h-bucker tone with its tone bleed capacitor can modify the overall sound. Not that this is a bad thing. Just go for it.

This is good, do this. But. Pop a diode where the coil pickup enters the 3 way switch or otherwise the top end from the preamp can sneak off down your tone circuit.(when both pickups are on) , and it can also go to ground when you roll off the coil volume.. Remember a signal will always follow the path of least resistance to ground, that other volume/tone circuit is a much easier path to ground than going all the way through the amplifiers circuit.

Because that preamp has a volume slider, if you do this you will have complete control in the middle position, able to roll either or both down a little. You might want a master volume as well, between the switch and the output jack, I probably would want it at any rate.

Plus yep, do what davidL says there about a trs jack cutting the battery power..

The best :)

Edit farmer Scott, doh, I didn't even see you'd put that already sorry mate
Thank you Wayfinder :0)

The power button is for the onboard tuner so you can tune the guitar without it plugged into an amp, rather than being an on/off switch for the whole preamp. It might work for the eq too as Scott suggests, but the addition of the tuner more than halves the battery life and will mean the tuning lights blink as you play notes. (It might be worth a try if you don't want to solder too much of the circuit and the addition of an on/off switch can be added later).

These eBay preamps are copies of the Belcat series of Prener preamps.

Here is a link to the Belcat Prener LC instructions

The link is for a 4 band preamp not 5 but check the measurements on the last page of the link to see if they are the same for your preamp as it gives a template which will make cutting the holes much easier.

Ok, guys, some news... Today I tested the preamp. First, David is right, the preamp turns on when I plug the jack, that's confirmed by the led you can see right under the grey buttons, it blinks when I do that. Secondly, the two greys button work just for the tuner: the "Power" button it's to turn on the tuner, while the "Note" button works to choose the note you want to tune (it's very useful for open tuning).

Anyway, considering it's a cheap EQ, it works pretty fine, and yes, it's a copy of Prener LC-5 preamp.

So, it looks I need an on/off switch, as David said, to connect the negative wire from the battery to the common ground from the whole circuit. I guess it's the best solution for the circuit to work, instead of using the onboard power button: as David said, the display it drains the battery, also it's annoying to see blinking leds when you play, unless you're installing the preamp on a Christmas Tree. :)

So David, if you could post a wiring diagram when you're on desktop PC, it would be helpful; besides could you post a link of the type of switch I need? I'd be thankful!

Thank you guys for all your answers, I'm glad to know that my question could be helpful for other users here.

P.S. This site and its users are awesome!

Hi Matteo,

I will dig out a spare preamp so I can take some photos (rather than try to describe it in words).
I should be able to add the info you need tomorrow.


Hi Matteo,

If your amp is wired the same as this one it has a fault with the wiring such that the preamp is always on.  If this is the case it will be much easier to add a switch.

Here you can see the four wires linking the EQ unit and the battery/jack module

From top to bottom

yellow B+ (positive battery connection)

whiteB- (negative battery which should be connected to one of the two jack socket sleeve lugs)

red OUT (live signal from the preamp going to the jack socket live lug which connects with the jack plug tip)

black GND (common ground which should connect to the other jack plug sleeve lugs)

So you can see better the 4 wire clip is removed and you can see a black wire from the battery (that I can trace going to the left of the white 4 point block to the lower right solder point for the jack socket) and a red + battery wire going to the yellow + of the 4 wire block via the circuit board (checked with multimeter).

The part we are interested in is the left hand side with the 1/4 inch jack connected ie the three left hand big blobs of solder.. Checking with my multi meter continuity function the signal live goes to the top blob.  Theoretically the battery black wire connects to the right of the lower blobs and then the lower left blob should connect to the white battery - of the 4 wire block so then the jack plug acts as a switch between these two connections.

On this unit the two ground points are permanently connected (both of the lower two solder points, the black battery wire, the white B- wire and the black GND wire are all permanently connected with or without a jack.  If I plug in a piezo rod to the EQ unit I can use test wires to an amp lead and without the plug inserted to the battery unit I can get a preamp signal using the top solder blob connected to the tip of the amp lead and either of the two lower blobs connected to the shaft of the amp lead jack plug.  This means for this unit the EQ is always on even when not plugged into an amp (and also explains why I was getting a short battery life).

If yours is the same it will make adding a switch so much easier. (if you have two test leads you can quickly check by the above method ie plug in the piezo rod into the eq and connect to an amp using the two wires to connect the tip of the jack plug lead to the top blob of solder and the shaft of the jack plug to either of the two lower blobs.  then tap and rub the piezo rod and listen for the sound transmitted through the amplifier).

This is (I think) how it should work

 If you find your peramp is constantly on then you can do the following

The black battery wire needs to be cut in half and add an extension wire to each to connect to the on/off switch and the power on/off is sorted.

To connect into the 3 way switch you solder a wire from the top blob of solder to the piezo connection on the 3 way and the ground is soldered to the common ground all the other grounding points are going to (back of the volume pot commonly).

You asked about switches any can be used such as a mini toggle switch (single pole single throw sp/st or single pole double throw sp/dt or a rocker type switch avoid any switch that is "momentary" as they don't latch and stay on)

some links but check on ebay for lowest prices 




If when you check your module works correctly (ie no continuity between the two negative blobs of solder on the jack/battery module let me know and I will draw up the wiring you need for that to work.

Anything that is unclear please ask.



Thank you David, my module is wired the same way as yours; the only difference is that I don't have any capacitor in the top right corner (as it shown in the photo).

I don't know if this could be an issue, I hope it's not, because the way you explained it looks pretty easy to do.
If it's not a problem, I'll try to check in these following days.

Regarding switches, I've found on eBay these two types. Are they good for my purpose? Which of them it's better?

Here are the links:



P.S. By the way, here's a picture I just took, to show you how my module looks.

Hi Matteo,

The first switch is no good (it is a momentary switch used for things like door bells or car horns - the signal only works when the button is pressed). The second type would work (I am not sure how you connect the LED bulb though as never used one).
Or these type if you can find a cheaper supplier http://www.ebay.it/itm/SPDT-ON-ON-Toggle-Switch-/161668550064?pt=LH...

The fact your jack/battery module is different makes me concerned it might be wired properly in which case you would need to hack into the battery circuit in a slightly different way.(connection to the 3way and common ground would be the same). Do you have a multimeter to check circuit continuity? Or are you able to check it is switched on without a jackplug inserted as described previously?

Ok, everything's clear about switches :)

Regarding the battery module, I'm almost sure the connection to 3-way switch and ground are the same; I should have a multimeter to check the circuit continuity, but I'm not sure about how to do that, I'd be thankful if you could explain what I need to do.

Unfortunately, I'm a wiring noob, I'm not able to check if the module it's switched on by the jackplug, but I'd like to learn this kind of stuff; if it helps, I can surely say when I plug the jack, the red led placed right under the grey buttons it blinks for a fraction of a second, the same whe I pull it out.


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