Piezo preamp for piezo bridge

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Hi there. I searched the articles but nothing found about piezo bridge for electric guitars.Anyway i have a LesPaul guitar with piezo bridge. Bought it from ebay. I need some advice for preamp. This is piezo bridge + boss me50.

Les Paul Piezo Test - YouTube

So not exacly the sound of lrbaggs or fishman like sounds. I need a compact preamp for better volume and tone. I installed 9v battery box and 3 way(on-on-on) switch for select piezo / pickup / both. So all i need is a preamp that increases volume simply. Sorry for my english.
 
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^^Looks like a pretty good choice, note also that you can place capacitance across the input to control output level and LF response. Start as is and add a few hundred pF at a time until you get the bass response you want. (This will also help tame the potentially high peak output of the pickup when you play hard, and also lowers the general output level.) If you cannot get the sound you want you may also increase/decrease the input resistor value, lower values of resistance will push the LF corner up, slightly reduce output levels, higher the reverse. Large values of capacitance reduce output levels, but extend the LF response. You may have to fiddle with both to get it right.

If you use LTspice or other similator, measure the capacitance of your pick up and model it as a voltage source in series with that value of capacitance, that will help you to understand the relationship between input resistance, capacitance, gain and LF extension. (I would expect something like -3dB @ 80Hz -100Hz might be a reasonable starting point, and it could end up significantly higher than that) Excessively extended LF response may result in thumping when you handle the guitar or play it. It's all about the right tradeoffs.

I designed piezo pick up pre-amps (amongst other things) at Fishman for a number of years.
 
A newbie question regarding this type of construction:

I created the pre-amp using this design
http://scotthelmke.com/Mint-box-buffer.html

- (I did change two components back so they were applicable for guitar rather than bass)
- my first try... ended up in pyrotechnics due to soldering the one capacitor in reverse phase
- after correcting this... I end up with a strange result... when I place the battery in... the guitar signal goes through... but it sounds identical to a standard cable... as if the pre-amp does nothing at all... but... if the battery is out then there is no signal

Did I make the wrong assumption to solder all grounds together? (including the negative 9V clip wire)

Also... since that first capacitor blew its top... could any of the other components have been damaged? They look fine.

-Lid55
 
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Hi Lid55, Were you expecting some gain? A buffer does not have any gain, what you describe is excactly what a buffer should do :) It is for matching impedances, has a high input impedance with a low output impedance, to keep both source and destination happy. It should not alter the signal in any way.

Tony.
 
I don't have an onboard active preamp in my guitar... though this is eventually what I am intending to do with this. I have modified my guitar (came stock with three magnetic pickups) to now include a piezo pickup (I installed a large piezo underneath the metal bridge piece). I do like the extended frequency range of the piezo, but the piezo by itself is thin sounding in the lows and is unbalanced in level compared to the magnetic pickups. A problem for a later date probably is that there is bleed from the magnetic pickups in the blend pot (at 0% magnetic and 100% piezo... I can still hear the mags a bit).

So my goal then is to use this buffer to increase the lows, and if it's possible, to increase the gain to match the magnetic pickup level. I guess I have confused these two issues and assumed the circuit would address both. Does anyone know if this kind of circuit can be easily modified and used as an amplifier as well as a buffer?

But besides that... the lows are still unaffected... the piezo alone still sounds thin.

Here are a few facts/details about the situation that might or might not be problematic:
- I soldered the negative/ground of the input, output, and the 9V clip wires together
- the transistor's "ground" lead was not wired to the ground (assumed that this is just a naming convention)
- I am using mono 1/4" cable connectors on both input and output

any ideas?
- BrettC
 
Sorry about posting before testing thoroughly... it does work (as a buffer)... but only at low levels it seems. I tried the buffer with my electric before and there seemed to be no effect (and as you pointed out... I was expecting a volume gain as well). I just tried the buffer with my acoustic guitar which has a single piezo element... and it does add a lot of low frequencies...

oddly... it doesn't seem to work on my electric guitar ... maybe because of the wire setup already in my guitar?
 
It doesn't work on both my electric and acoustic guitars, that's the point I'm trying to make.

Anyhow, my next step is to do the breadbox/prototype thing... testing the circuits as I go... it is new to me to think of elctrc guitar guts as an extension of an outboard circuit...
 
So I just think I should add that... after more testing (two different piezos)... this buffer circuit is actually quite amazing / works well (http://scotthelmke.com/Mint-box-buffer.html)... it only cost me about $10 in parts (with lots of leftovers) and probably five hours research and soldering.

I am surprised to find how necessary it is for the buffer to immediately follow the piezo.

But of course.... it works excellent as a BUFFER and not as a PREAMP!... lol... won't make that mistake again...

So heres a thanks to Walter Harley and Scott Helmke wherever they are. Salud!
 
that's what i thought ... a piezo can only work with active onboard curcuit

No, that's completely untrue.

but then, why do they build combos with special hi-z input of several mega ohm intended for piezos :confused:

So you can plug a piezo straight in - your initial premise is completely wrong.

Personally I would suggest you're far better off having a buffer as close as possible because the high impedance means it's far more susceptible to interference, and the capacitance of the cable leads to high frequency attenuation.

So if you're NOT using a buffer, then make sure you use as short a cable to the amp as you can, and that it's very well screen and low capacitance.

It's a lot easier to bung a buffer in though, a simple single FET and a couple of resistors and capacitors is all you need, then you can use cheap and long guitar leads.
 
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No, that's completely untrue.

So you can plug a piezo straight in - your initial premise is completely wrong.


maybe
ofcourse I would also expect it to 'work'

but since it needs a preamp input with minimum 4M ohm, or maybe even better with 10M, then I would expect it to suffer in a passive bass guitar

so I reckon its natural 'raw' impedance is very high

but knowing the difference between series or parallel connecting the split coils of a P bass ... maybe it would work fine if just parallel connecting with a J neck pickup (or similar) :scratch2:

well ... I'm mostly only interested because I have a real stupidly long shortscale neck that apparently leaves very little room for pickups
 
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