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Piezo Acoustic bridge project.......


BeAR

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Ive been toying with the idea of a piezo type bridge in an electric guitar for a while now and Im starting my next project.

It basically consists of 2 piezo transducers epoxied to the inner side of my Strat bridge. Running inside the main cavity to a small pre-amp (9volt), controlled by an independant volume knob which will replace on of the tone knobs on the Strat. The pre-amp is in the design stage ATM, but should be finished in a week or so. The output will consist of a stereo jack socket in place of the original mono one. I'll use a special tip ring sleave Y cable to split the regular output from the piezo output.

The piezo's I used started life as $2 buzzers from a local electronics store. I simply took them out of the plasic housing they came in.

Testing was done by literally taping the 2 piezo's to the body of one of my guitars and running the outputs straight into my amp. Simple.

Sounds ok but kinda weak. Alot of vibration is lost between the strings and the timber, especially with the Floyd Rose on the particular axe I tried.

Next I taped them to the cast block under the bridge......what a difference! Ballsier sound and quite nice too. Fixing them to the Strat bridge with epoxy will transfer the maximum string vibration to the transducers. A little EQing at the pre-amp stage should tailor the sound nicely.

Looking at the guitar you wont be able to tell there is anything different about it which is cool.

The best thing is Ill have a nice axe to record acoustic parts with, without the strain of trying to get my electrically spoilt fingers around an acoustic neck!!!! Or maybe I could wire it differently......................electric CRUNCH..........flip a switch..............acoustic bliss :D

Ill post some pics when time permits.

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hmm, that looks easy and sounds alot cheaper than these retrofit kits, where did u get your transducers again, out of what????????? because strat like saddles are usually like what bout a 100 bucks for a set to replace on a trem block, plus then you have to add the preamp which is what about another 100 bucks or so? btw is this a homebrew preamp or is it something you constructed yourself, more info on the way you wired the preamp and its componets etc.... would be greatly appreciated!!!! :DB)B):D I have always wanted to incorporate a piezo system into my strat, it sounds like you have done it for much less than what I had figured it would cost, wow, this info is worth more than gold, i love this site/forum

jeremy

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This is going to be interesting to see how it all turns out.

I've had the pleasure of working on a couple of double edge trems in the past, the biggist difference I'm seeing is the lack of a signal path board and also they wire the individual pickups inside each of the saddles themselves.

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Jeremy, the transducer came from an electronics store. It the element out of a piezo buzzer, only costs a dollar or two each.

Ive also had a change of mind about the pre-amp. I finished installing the setup into the guitar running passively and the bridge is giving a very hot signal :D . Im not sure the preamp is necessary. I wont have the neck on the guitar until the weekend so Ill make a recording with it when I do.

Heres what I did to wire it up.

1. Bought a 500k push/pull pot with DPDT contacts (double pole, double throw.)

2. Wired it in place of my existing volume pot.

3. Grounded the earth side of the piezo bridge to the volume pot case with the other pickup earths as per normal.

4. Here the clever part.....................remove the center pickup hot wire from the 5 way switch.

5. Wire the center pickup hot wire to one side of the Push/Pull pot switch.

6. Wire the piezo bridge hot wire to the other side of the Push/Pull pot switch.

7. Wire the push/pull pot common wire to the tag on the 5 way switch that used to have the center pickup wire.

Now what happens is this. With the push pull pot in, the guitar acts just like a regular Strat.

With it out, the center pickup no longer works but the piezo takes its place. Pos 1 is the bridge single coil, 2 is the bridge single coil and the piezo pickup, 3 is the piezo on its own, 4 is the piezo and the neck pickup, and 5 is the neck pickup.

This should give some nice combinations of pickup tones. Good thing is the tone and volume controls will have an effect over the piezo sound aswell as the regular pickups.

I'll report how it all works after the weekend.

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sounds good ,

i was thinking more along the lines of , as you said before , replace one of the tone controls with a volume for the piezo system, that way you can have even more blends of sound , and of the 5 pickup combinations with or without the piezo and any combination of volumes. what do you think? would that work also?

i dont know what way the tone controls are on a standard strat, but mine is a fat strat , so the first tone knob controls the neck pickup, the second one controls the middle pickup ,and the bridge(humbucker) has no tone control.

so can i simply use the one tone control for both pickups? or would the pots have different values?

thanks,

john.

(p.s , the transducers are wired paralell yeah? , just checkin)

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I would highly recommend adding a pre-amp for your piezo system. The piezo has plenty of output but is a very high impedance device (about 1Meg) and wiring it directly on to a potentiometer will load it differently across the range of the pot which will result in different frequency responses for different volume settings.

A colleague and I have just modelled a similar system on software and buffering the piezo with a preamp makes a huge difference.

I would suggest using a jfet buffer directly off the piezo. Have a look at this link: http://www.cafewalter.com/cafewalter/piezo.../oppiezobuf.htm for some designs.

You can then follow the buffer with a pre-amp with tone controls for equalisation. A gain of one through all this is fine as there is plenty of output from the transducer and the only thing to worry about is getting a decent frequency response out of the system in to the amp (we don't want to overdrive the amp here, this is acoustic type sound not death metal), even the length and impedance of the cable will make a difference with a 1meg impedance source.

I am about to fit the system to the acoustic guitar I am building. I have a modelled design of the tone circuitry if anybody is interested. I will be building it and testing soon.

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Hi Keith, thanks for your input.

Im unable to test the output of the raw piezo ATM as Im still waiting for my neck to get back from getting refretted. Hopefully tomorrow.

I see your point about the piezo load and I figure your prolly right. For the sake of a few dollars worth of parts I might try out your design and see how it sounds. My main goal was getting an even sound across all string with a ballanced output, however large.

Tailoring the sound wasnt primarily a big concern for me as I was only intending to use the guitar for recording DI'ed into my mixer. I was gonna EQ from there.

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What I would suggest is: Put the JFET buffers as close to the piezo's as you can. There should be room for a tiny circuit board in a Strat with a 9v battery. Trim the outputs of the buffers with trim pots mounted on the circuit boards to get a good balance. Replace the Strats jack socket with a stereo one and wire the magnetic pickups to one channel and the piezo's to the other. You can then plug a stereo cable through to the equalisation box which could be clipped to your strap or on the floor with your other effects.

If there is still not enough room in the Strat for the 9v cell it is possible to feed the power on the output lead. I would have to discuss this with my audio expert colleague and come up with a good design. The important thing is to keep the high impedance bit short. ie from the transducers to the FET buffer.

Keith

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  • 3 weeks later...

I'm not 100% following the exact procedure going on here, I guess because I can't visualize all of the parts. Running the risk of sounding like a moron, could someone post a full shot of what the complete circuit would look like?

I'm in the middle of refinishing an Ibanez RG770, and I would love to install a piezo somehow without having to replace my Lo Pro Edge tremolo. I don't have a use for the tone knob, so that spot would be open for a piezo pot if necessary, and since I've got it completely dissassembled, I can do any rerouting work now that may be needed. Ibanez makes a "Double Edge w/ piezo" bridge, but sells it exclusively on their new guitars, no exceptions.

Any help would be greatly appreciated. :D

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What I would suggest is: Put the JFET buffers as close to the piezo's as you can. There should be room for a tiny circuit board in a Strat with a 9v battery. Trim the outputs of the buffers with trim pots mounted on the circuit boards to get a good balance. Replace the Strats jack socket with a stereo one and wire the magnetic pickups to one channel and the piezo's to the other. You can then plug a stereo cable through to the equalisation box which could be clipped to your strap or on the floor with your other effects.

If there is still not enough room in the Strat for the 9v cell it is possible to feed the power on the output lead. I would have to discuss this with my audio expert colleague and come up with a good design. The important thing is to keep the high impedance bit short. ie from the transducers to the FET buffer.

Keith

i was thinking more along the lines of using a stereo jack , but wiring the magnetic pickup output to one channel and grounding the piezo J-fet buffer to the other , this would mean that the battery would not drain when the guitar is plugged out , but alas would not allow stereo seperation .... i dont mind.

im thinking of including such a system in the bass im building.

p.s , does anyone have any good schematics of pre-amp systems with Eq controls ?

thanks,

john.

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I have a schematic for the preamp with equalization. e-mail me and I'll give you a copy. We designed and modelled it on software and I have not built it yet. The acoustic guitar it is going into is not yet ready for the electronics yet.

Have a look at Piezo Buffer for a design for the buffering of the actual piezo wafer.

Keith

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Interesting thread this. I experimented with a couple of under saddle piezo strips, as used on electro acoustics, but had little joy. In the end for my strat, I plumped for the Graph Tech saddles with piezos and preamps, wired to a stereo jack so my mag pickups go to the guitar amp, while the piezo output goes to the mixer. Bit fiddly - had to rout a little more room in the control cavity for the preamp, plus a hole for a battery box behind the bridge on the reverse. Apart from having to use a custome cable, and also wanting the same on my tele, it's wonderful. Even with time included, it cost me less that the powerbridge equivalent and sounds as good.

This project is closer to my original idea, so keeping an eye on it for the tele in a few months! :D

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Ive been using a Parker Nitefly for about a year now. Basically I started into it because I have a Tacoma RoadKing that im not thrilled about dragging around. (ive yet to play an accoustic since that i like anywhere near as much.(Taylor,Takamine,Larivee,Breedlove included)

What I expected was to use the accoustic sounds live for a comfortable stage guitar. I was immediatley impressed by this use, so were my bandmates. What was also clear right away was that it was good for a whole lot more.

It can get some wicked boost to electric tones. Really cool percusive effects, thicken up wierd rythm parts. Once you have one its hard to understand how you lived without it.

There is a downside, when switched on it makes noise, not hum. Its sensetive to movments on the guitar, grabbing the arm, palm mutes, etc... So if you put one in make it switchable.

I read about this concept years ago with the buzzers and electret mikes. What I want to try is to put one in the neck pocket. They are presure sensetive devices the neck pocket and under the bridge plate of a tele always seemed the place.

I think I have a schematic for a preamp somewhere that i can email into the webmaster for posting.

John :D

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I've the probs with the 'noise' as well, exactly as you say. I roll the bottom off to get rid of some of it. Mine's on a 3-way micro switch, so I can any combination of electric, both and acoustic. I gigged the guitar tonight actually, and you're dead right about the added dimension it adds to the electric sound - it makes the strat almost more stratty on some tones, while on others it gives a really credible Rickenbacker 330 sound! Lot cheaper too...

On the neck pocket idea, I'm sure I read a Zappa article many years ago, in which he was talking about the ex-Hendrix Strat that his son is hawking around auctions. I'm 99% certain he said that at one time he had fitted a Barcus Berry contact piezo ansducer into the neck..

:D

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and by the way, the volume pot on the strat has one of those little circuits across it which keeps the treble up when you turn the volume down. The middle pot is a mid cut/boost now, while the rear tone pot is now the volume control for the piezo. I've got the mini switch (a DPDT as mentioned earlier in this thread) between the p/u selctor and volume pot. With hindsight, it's a little too easy to flick when grabbing the volume B) , so I'd move it further back should I ever change the pickguard.

:D

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  • 2 weeks later...

hey guy's I'm really interested in fitting a similar system to this into my jackson. I went out and bought 6 buzzers to play with, and I havent fitted/tested any yet, just taken a couple out of thier plastic housing. I was just wondering, the buzzers I have come with the thin wafer element, but also a small PCB board on the back with 3 resistors. Is this an integral part of the transducer, or a seperate preamp?. Also, I was wondering if you guys could hook me up with a possible wiring config for my control setup. It used to be vol/tone/5way, now its just the vol and 5 way, with the vol where the tone used to be. I randomly bought a DP3T, on/off/on switch and have mounted itwhere the orignal volume knob was (ala petrucci, kinda) and would kind of like to have it as a neck pu/mag piezo blend/bridge pu switch, but I dont know if this is possible(mainly cos of the off pos.). Any suggestions from you guys? I was also toying around with the idea of putting the tone capacitor on one of the 5 way contacts, if I ever wanted to rop all my treble, but I dont know how to wire this stuff up. Its an H/S/S config guitar with a duncan JB in the bridge, thanks for anything you might have :D

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