Hi everyone. I'm looking for a preamp diagram for a piezo pickup. I'm looking for a schematic that works with 48v phantom power connected to a mixer. I need it to have a good bass response. The purpose of this circuit is to experiment with the possible amplification of a wooden box used for percussion in live concerts. It seems like a good idea to build the preamp with FET transistors, rather than with integrated circuits. Any ideas are welcome.
You can also experiment with the so-called "exciter" speakers, meant for driving sound into a panel. They work in reverse also, as a sound pickup. I've got - at times - pretty good sounding, deep response out of these, attached to the soundboard of an acoustic guitar.
They also break, as a guitar moves about when played and these things are basically a heavy magnet dangling off a spider suspended voice coil. If the "box" is something like a Cajon, where someone is sitting on it and stationary, that shouldnt be as much of a problem. If on a strap and mobile with the percussionist - they can run about the stage with it - you'll have to figure out how to support the magnet part without mechanically short circuiting it to the board it's picking up sound off of.
I've found the exciter voice coil winding drives the low-Z, balanced input of a mixer no problem. No need for any support amplification at all, just good wiring practice. Connect ground to the exciter's metal frame, if it has one.
Something like this, with helper feet to support the heavy magnet part;
I have one of these in a guitar now, but I broke off the additional support feet to get more placement latitude between the guitar soundboard bracing pattern beams. 8 Ohm ones are going to have a bit better signal than a 4, as above.
They also break, as a guitar moves about when played and these things are basically a heavy magnet dangling off a spider suspended voice coil. If the "box" is something like a Cajon, where someone is sitting on it and stationary, that shouldnt be as much of a problem. If on a strap and mobile with the percussionist - they can run about the stage with it - you'll have to figure out how to support the magnet part without mechanically short circuiting it to the board it's picking up sound off of.
I've found the exciter voice coil winding drives the low-Z, balanced input of a mixer no problem. No need for any support amplification at all, just good wiring practice. Connect ground to the exciter's metal frame, if it has one.
Something like this, with helper feet to support the heavy magnet part;
I have one of these in a guitar now, but I broke off the additional support feet to get more placement latitude between the guitar soundboard bracing pattern beams. 8 Ohm ones are going to have a bit better signal than a 4, as above.
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Thank you for this interesting information. The first idea is to amplify a small wooden box with internal springs that emulates a flamenco cajon. The box is smaller, about a quarter of the size of a cajon to sit on, but a musician can carry it hanging. Regarding the Dayton speaker, I have a question. In principle, I understand that you are talking about connecting the speaker directly to the mixer; my audio inputs are XLR. With an impedance of only 4 ohms, if the 48v phantom power is connected by mistake, the mixer will practically be a short circuit. Isn't that true?
You're welcome. I believe that +48 volts is applied equally to the two balanced signal pins, with ground being the negative or return. Ordinary dynamic mics dont burn, nor does the mixer when "+48 phantom" is turned on, as there's no path to ground from the balanced signal ordinarily.
They figured "It's going to happen" (+48 phantom on/off, regardless of what's out at the cable end) so they designed it accordingly.
Below you can see what I mean schematic wise, as lifted from the Shure website. Pin 1 is "ground" or "return", 2/3 are the balanced signal, what would be connected to the dynamic mic's coil or exciter speaker coil.
An electret microphone or mems setup on a small board with preamp 3.3 to 5v
Arduino 20 to 20khz response.
If you need to use 48v you will need a step down regulator as well.
Arduino 20 to 20khz response.
If you need to use 48v you will need a step down regulator as well.
I think you can start with a basic condenser mic preamp like the one below, it is phantom powered.
Since your pickup is piezo you do not need C5, C6, R7, R8, R9.
J112 instead of obsolete 2SK170 should be fine here.
I think R10 >10MOhm should be OK too. Wire your pickup in parallel with R10.
The low (bass) output may need extension - increase C1..C4 2..5 times, though I did no calculations.
Since your pickup is piezo you do not need C5, C6, R7, R8, R9.
J112 instead of obsolete 2SK170 should be fine here.
I think R10 >10MOhm should be OK too. Wire your pickup in parallel with R10.
The low (bass) output may need extension - increase C1..C4 2..5 times, though I did no calculations.