Guitar piezo preamp

[RipX]

Hi,

I want to build a cheap preamp system for my guitar. I have seen this piezo transductor : TRANSDUCTEUR PIEZO 3 A 30 VAC - Elecdif.com
But now I want to build a preamp for this ch*t

I have seen this post : http://www.diyguitarist.com/PDF_Files/FET-PiezoPreamp.pdf

Idealy, I want to build a model like this but with an adujstable gain. So, carac :

- 9V battery alim
- for piezo
- built in the guitar
- with an adjustable gain and a on/off button
- cheap !

Can you help me to find this product please ? Thanks !

 

[Frank Berry]

That is not a piezo microphone. It is a piezo alarm ... a very loud whistle!
You will need a piezo microphone and a preamp to provide gain control and a low output impedance.
Rather than a piezo element, you may want to use a condenser microphone element as they produce better fidelity and they are quite inexpensive.

 

[RipX]

Hi, thanks for this advise !
I want something pretty good but cheap, can you explain your idea with links of condenser micro element and a thread/pdf for build the preamp please ?

Thanks

 

[kevinkr]

You'd generally use piezo either in an under bridge transducer or as individual under saddle transducers.. You can also use them in the body of the guitar. Note that acoustical pick up with a mic on the guitar can be tricky to handle due to feedback..

You may be able to modify that piezo buzzer for use as a body pick up by removing it from the housing and mounting directly on the body. Is this an acoustic or solid body guitar?

 

[chrispenycate]

What will the preamp be driving into? If it's a further preamp with gain control and tone, you could probably just run the output of that buffer into a pot (replace the 10k resistor by a 10k pot to ground, wire the wiper to the output jack) If it's driving a power amp you're going to need more gain, and probably tone controls (I've never heard a pickup that sounds decent without equalisation).
A piezo is normally a contact mic; it takes the vibrations from the body of a guitar, or sometimes the bridge. I used to recuperate from crystal record player cartriges, and they didn't sound any worse than things like the Barcus Berry hotdot, but placement is critical – a couple of centimetres difference, and you get a whole different set of resonances. The electret gathers air vibrations, so the sound is more accurate – but if you mount it in the sound hole, you get what a guitar sounds like in the sound hole, which requires some treatment before it's anything like what a guitar sounds like from anywhere you might listen to it normally. The electret will feed back earlier, but has it's own preamp incorporated, so really only needs a potentiometer and wiring up (unless, as I've previously said, it's driving straight into a power amp).

Et tiens, il est parti. And I see someone types faster than me, though with many of the same opinions.

The problem I always had was how to mount the battery without damaging the instrument; I just hate having to take all the strings off to change it. I finished up putting XLRs on the instruments and phantom powering them from a box on the back of the stage (which also held the equaliser). Overkill, probably.

The standard on/off switch (which is horrible but does work, usually) is a three pole jack socket on the instrument, so plugging in a standard two connector guitar lead shorts between ring and sleeve, and makes the ground connection. Thus, unplugging the guitar removes your battery drain. You can even buy jack sockets with make connectors on them as well as break – or, if the instrument's going to spend the entire set plugged up and ready, for just one number used, it's easy enough to add a discrete switch. Less messy than the volume control, anyway. Perhaps a rechargeable battery while it's on the stand so you never need to open it up.

Piezos are capacitive (almost perfectly). Contact mics are frequently boomy (not the bridge ones, the panel ones). Changing the input impedance changes the low frequency response -bingo, equalisation.

As placement in the instrument is so critical, it's generally a good idea to set everything up outside the instrument, with an amplification system, and try sticking the mic ti different points with chewing gum (all right, bluetac). I can do diagrams if absolutely necessary, but I'm no artist.

 

[RipX]

Hi guys, thanks for all !

It's an acoustic ukulele. i'm not a pro but I have a folk with a preamp, just one buton for gain, all integrated in the guitar. I plug the cable to a guitar amp and it's working fine ! I want this ...
I think "You may be able to modify that piezo buzzer for use as a body pick up by removing it from the housing and mounting directly on the body." it's a good idea and "unplugging the guitar removes your battery drain" it's a good idea

What type of material can work for me ?

Thanks

 

[Struth]

Hi Guys

As stated, peizo pickups are capacitive. You just need a jfet buffer to capture the full tone, then place a volume pot after it.

If you've tried the raw peizo into a standard guitar amp input or anything else, you'll get a weak signal that has no bass at all. This can lead you to the mistaken impression that a lot of gain and bass boost is needed. However, all that is required is a very high input impedance >10M. If you really need gain, then use a jfet input opamp. These pull more idle current than a single jfet unless you use a low-power version, but then the sound quality is much poorer.

There is an acoustic preamp project in "Tonnes of Tone" (TOT) on my site. This project was also published in Guitarist magazine in the UK back around 2004.

Have fun
Kevin O'Connor

 

[RipX]

Hi and thanks ! Sorry but I have not the budget for this preamp !
So, to make it simple :

- What mic I need ? Piezo or condenser mic or something cheap like this ?
- And, have you a preamp design or how to build for this mic ?

Finally, I think http://www.diyguitarist.com/PDF_Files/FET-PiezoPreamp.pdf is not so bad ... but I like a pot for gain control and a system for stop the battery drain when I unplug the câble !
I think it's not very difficult to find for a pro like you guys

Thanks

 

[Nigel Goodwin]

Finally, I think http://www.diyguitarist.com/PDF_Files/FET-PiezoPreamp.pdf is not so bad ... but I like a pot for gain control and a system for stop the battery drain when I unplug the câble !
I think it's not very difficult to find for a pro like you guys

It's a bit of a bizarre circuit?, the switched gain at the input halves it's input impedance, and only has a very minimum effect. Also there's the strange comment to change R4 to 220K for bass guitar? - crazy!!

Simply remove the input switching and 4.7M resistors, and stick a volume pot on the output to make it adjustable volume - personally I think 22K for R4 sounds too high, and I'd make it lower whilst checking the source voltage (aiming for around 4.5V).

 

[Struth]

Hi Guys

The peizo buffer costs less than a dollar, even with a volume pot on its output.

Use a TRS jack - tip,ring,sleeve, aka 3-circuit jack. Sleeve ties to circuit ground, tip to volume pot wiper, ring to battery negative. When you insert a mono 1/4" plug, the ring and sleeve are shorted and the circuit is powered. Unplug and the battery disconnects.

Micorphones that mount on the instrument are probably about the same price or more than a peizo pickup for under the bridge. A mic preamp is more expensive than the peizo pre as the mic requires significant signal boosting to even be as high as an instrument pick up - about 30db of gain. I don't see how this is less expensive than the other, except for possible labour savings if you have to pay someone to mount the peizo.

Have fun
Kevin O'Connor

 

[RipX]

Hi, thanks for the tips !
So I choose the piezo mic. For the preamp Struth have good idea !
I think it's possible to modify my "diyguitarist preamp" for adapte to my use ? (like Niguel)

Thanks

 

[RipX]

I try to modify the original shematic and I have some questions :

- What is the value for the pot ?
- What is th value for R4 ?

And, my shop has not piezzo mic, but I have found this on the net L'ATELIER DE LUTHERIE FABRICE GOUGI/Shretler/Micro pas cher and my store has the piezzo parts ... good idea ?

Thanks !

 

[JMFahey]

If you want to add a piezo sensor to your Ukelele spending little, you can:

a) pull the piezo disk from that alarm buzzer you show, you'll have to clean it because it's usually glued with silicone adhesive (Silastic) and glue it to your ukelele from the *inside*, below the bridge.
It involves some dexterity , maybe you'll need a Luthier friend to help you.

b) build a simple FET preamp.
There's a model of which I built hundreds (lots of Tango and Folkloric music Guitar and Fiddle players around here) and I can give you the PCB and layout design; no schematic needed because it's so simple, but you'll need to make your own PCB.

It has volume and Treble/Bass "trim" controls, in the tradition of the original Barcus Berry preamps, but you can build it with Volume only.

9V battery powered, of course, and very long battery life.

I usually glue a piece of Velcro to the inside of the guitar back (you can see it straight through the soundhole) and the matching strip to the battery itself (which lasts over a year in normal use) .

Or you can mount only the Piezo inside the Ukelele, connect it to a jack (regular or 3.5mm) , build the preamp in a small box and attach it to the instrument strap, or even carry it in your shirt pocket or your belt.

Je suis Francophone mais même ça écrivez en Anglais.

 

[RipX]

Hi,

L'anglais c'est dur pour moi, mais bon c'est en écrivant qu'on s'améliore
Thanks for your reponse :

a) Really, I just opened, remove plastic enclosure, clean and it's all ? I have a piezzo mic ?

b) Please, if you have this, it's PERFECT

I want all built in the ukulele, more practice for daily use !

Additionnal and for my electronic learning, I like have a respond to my last questions for the modification of the preamp :

- What is the value for the pot ?
- What is th value for R4 ?

Thanks for all

 

[JMFahey]

OK, I'll convert my .PCB files to some graphic format and add some cm. scale inside so you can print it real size with a Laser and make a toner transfer PCB.

I designed it over 15 years ago on DOS based PCB software (even EAGLE was DOS based ) so it takes some format juggling to make a .gif or .png out of it .

You can use just the Volume pot or all 3.

The PCB is very small, the size of your little finger, and "hangs" from the pots, so you need no additional mounting.
It uses 3 x 16mm pots for compact size.

As a free sample, (later I'll send you the actual copper etching and silkscreen B/W artwork), this is just a screen capture of what RIMU "reads":
PzoPre2-RGB.png

By the way, the Spanish labels will be easy for you
Ag: Agudos:Aigu
Gr: Graves: Grave
Sa: Salida : Sortie
Vo=Volume

EDIT: as of the Piezo mic, inside that buzzer round plastic box you *should* find a round brass disk, with a smaller piezo disk attached to it, glued around with some flexible transparent silicone sealant.
They mount it this way so the center is free to flex forward and back to make sound.

Once you have the clean disk, brass is ground and the ceramic has a very thin metal layer, to which a contact wire is soldered, that's your "hot" terminal.

Be careful because overheating this solder point will make it fall off.
Use a small solder iron, pre tin the wire and just tack solder it to the ceramic contact.

Then you can glue/epoxy the brass side to te inside of the Ukelele .

 

[RipX]

Thanks for all, i'm waiting for the pcb now You're pro !!

 

[JMFahey]

OK; here's the PCB.

Here I show everything from the copper side, I added "rulers" so you scale your drawing on the paper.

*Best* quality, by far, is with photosensitized "Positive" PCBs.

You print the tracks/copper side as-is on a transparency or drawing (Vellum) semi-transparent paper, sandwich it over the sensitive side and expose and develop according to instructions.

PRO results, and usually the hardened resist can be left, because it protects copper from oxidation and evaporates with solder, works like flux.

*If* you are experienced with thermal Toner Transfer (avec un fer à repasser), go for it, but you must "mirror reverse" the drawing when printing.

I have no step by step instructions, these images should be enough, I have no "Hobby" page nor sell kits. (Nor Books )

An externally hosted image should be here but it was not working when we last tested it.

NOTICE: the resistor leads are bent into a "U" shape and they are mounted "Vertical" to save space.
The "circle" in each shows the body and the "line" is the bent lead.

 

[JMFahey]

I forgot some details:

1) these tone controls are "cut" type (similar to what's standard in millions of passive guitars).
The *real* tone control is the one on the amplifier or mixer; these on the preamp allow the musician to cut boominess/shrillness/low or high frequency feedback without depending on the Sound Operator.
"Boost" contols are dangerous, can easily cause uncontrolled feedback, and *that* makes the audience angry.

So these tone controls must be used on full (on 10) and you cut shrillness or boominess as needed.

If you want the simplest (always flat) preamp, do not mount Treble/Bass pots , and bridge the bass one with a wire jumper.

*Really* the tapers should be: Log/Audio "A" for Treble and Volume and Reverse Log "B" for Bass, but easier to find Linear "B" are adequate.


2) I used a 1M input resistor, which is more than enough for a large piezo such as the one recycled from a buzzer or wristwatch alarm.
Those typically have around .1uF capacitance, do the math. (.1uF / 1M)

*If* you have a very small piezo then you can rise input impedance up to 10M .

3) use a stereo jack to switch the 9V battery, the Pedal Sites have ample info about it.

Good luck.

PS: if you want to make a couple with Thermal Transfer, I can post a drawing to print 4 or 8 at once, the PCB is *real* small anyway.

I usually make batches of 16 or 32 and give a few to good customers.
Easy, they fit in a single A4 sheet or coated printing paper and it's the same to make 1 or many.

 

[RipX]

Thanks for all

I use photosensitized copper with pnp blue paper, toner printing and thermal transfert. Usually it works not so bad

1) I want to build this into the ukulele, and I wanted tu put just the volume pot with a little dial just glue below the rosace ... Do you understand my idea ? Working ? For the another pots, if I have good understand, I must bridge the pots with a wire ? But the 3 points or just 2 ?

2) What is the size of a conventionnaly large/small piezo ? I think I want recycled a buzzer

3) As advised up in this tread, I can use a TRS jack for stop drain battery, right ?

I want to build just one, I believe, for the moment, but thanks

Thanks, for all, I go to my electronic shop ! If you want, I can post photos of the finished preamp in one or two weeks

 

[JMFahey]

Thanks for all

I use photosensitized copper with pnp blue paper, toner printing and thermal transfert. Usually it works not so bad

1) I want to build this into the ukulele, and I wanted tu put just the volume pot with a little dial just glue below the rosace ... Do you understand my idea ? Working ? For the another pots, if I have good understand, I must bridge the pots with a wire ? But the 3 points or just 2 ?

Ok.
The tone pots actually use only 2 legs , the third is already bridged to the center one.
To keep them out of action, you simply do not use the treble one, no added link, nothing and bridge the two "free" holes for the bass pot with a little wire.
Then both are set to "max"="flat".

Not your case, but some users who wanted no holes/pots in their instruments , have also avoided the Volume pot, bridging midd>max holes, and wrapping the small PCB in foam (or cardboard ) and just dropped it inside some cavity.

I forgot: you can use practically *any* N Channel FET: 2N5457/MPF102/BF245/BF256/2N(PN)4391 or any from their families.
Just check the pinout and if necessary rotate or slightly bend its legs to fit in the proper holes.
Remember the tracks and the layout are seen from the copper side. (as if the PCB is "transparent")
I find it easier to avid errors that way, because you see what's connected to what all time long.

2) What is the size of a conventionnaly large/small piezo ? I think I want recycled a buzzer

Commercial Piezos are usually very small, or the "toothpick" type put under the saddle, while recycled buzzers are 15 to 20mm diameter, much easier to mount.
Most important: their large size gives higher signal and higher capacitance (lower impedance) so they are much easier to interface.

3) As advised up in this tread, I can use a TRS jack for stop drain battery, right ?

Yes, check what floor pedals do.
Basically the +9V terminal is always connected and the - terminal goes to the "unused" or "ring" terminal in a stereo jack.
When you put a mono (standard guitar) plug there, its body bridges the "extra terminal" and ground, turning the preamp on.

I want to build just one, I believe, for the moment, but thanks
Thanks, for all, I go to my electronic shop ! If you want, I can post photos of the finished preamp in one or two weeks

Please do.

Just as an example, these are 2 Double Bass players using my systems, the first one is a Jazz player,

the second plays in a Symphonic Orchestra in Germany.

Neither of them wanted holes in their cherished instruments so the preamps were built in small "pedal" boxes.