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Old 19th June 2013, 04:02 PM   #11
RipX is offline RipX  France
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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
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Old 19th June 2013, 08:25 PM   #12
RipX is offline RipX  France
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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 !
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Old 20th June 2013, 07:08 AM   #13
JMFahey is offline JMFahey  Argentina
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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.
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Old 20th June 2013, 08:08 AM   #14
RipX is offline RipX  France
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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
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Old 20th June 2013, 03:25 PM   #15
JMFahey is offline JMFahey  Argentina
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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(n)

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 .
Attached Images
File Type: png PzoPre2-RGB.png (58.7 KB, 120 views)

Last edited by JMFahey; 20th June 2013 at 03:37 PM. Reason: Forgot mic.
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Old 20th June 2013, 06:26 PM   #16
RipX is offline RipX  France
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Thanks for all, i'm waiting for the pcb now You're pro !!
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Old 23rd June 2013, 02:39 AM   #17
JMFahey is offline JMFahey  Argentina
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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 )

Click the image to open in full size.

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.
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Old 23rd June 2013, 03:30 AM   #18
JMFahey is offline JMFahey  Argentina
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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.
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Old 23rd June 2013, 08:40 AM   #19
RipX is offline RipX  France
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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
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Old 23rd June 2013, 01:16 PM   #20
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by RipX View Post
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.
Quote:
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.

Quote:
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.

Quote:
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,

Click the image to open in full size.

the second plays in a Symphonic Orchestra in Germany.

Click the image to open in full size.

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