Piezo transducers as mics, wiring and amplification.

[Tone Deaf]

Hi Guys.

Anyone any good with electronics and amplification? Please be gentle with me as I have very little experience when it comes this.

I have some questions regarding piezo transducers used as contact mics. I’m interested in various applications and am thinking of wiring three and five piezos together.

Am I right in thinking that piezos produce a relatively high output voltage but extremely low ampage and is this why piezos require a preamp?

How should they be wired together series or parallel? If parallel and on the same instrument, or environment recording the same source, will the increase in the power output of the ‘array’ be enough to negate the need for a preamp before amplification for headphones?

If you’d still require a preamp, could you use the same one for 1, piezo on it’s own, and / or 2, 3, 4, 5 piezos wired together.

Could you Bluetooth from a preamp to a monitor or Bluetooth headphones or would the signal have to go through an amp first? I’m sure answers will generate more questions so your indulgence is appreciated. Thank you kindly troops. 

[TwoTimesBass]

Hi Tone Deaf,

I'm not an expert but i can give you a few pointers for further research.

4 hours ago, Tone Deaf said:

Am I right in thinking that piezos produce a relatively high output voltage but extremely low ampage and is this why piezos require a preamp?

Sort of. Piezos do produce a much larger open-circuit voltage than for example, a dynamic mic. The key element you need to consider is impedance. Piezos generally have a very high impedance relative to typical input sources, which is why a preamp is used between a high output impedance pickup and lower amp/mixer input impedance.

Quote

How should they be wired together series or parallel? If parallel and on the same instrument, or environment recording the same source, will the increase in the power output of the ‘array’ be enough to negate the need for a preamp before amplification for headphones?

You can wire 'mics' together in series or parallel, but again you need to consider the impedance this presents to the input of the next bit of kit down the line. You'll either be raising (if in series) or lowering (if in parallel) impedance each time you add another mic. Most line inputs such as you'd find on a headphone amp are around 600 Ohms, so no, you won't get low enough to make that work. The complex phase interactions between multiple piezos on the same instrument are also worth bearing in mind.

Quote

If you’d still require a preamp, could you use the same one for 1, piezo on it’s own, and / or 2, 3, 4, 5 piezos wired together

Yes, subject to everything above.

 

4 hours ago, Tone Deaf said:

Could you Bluetooth from a preamp to a monitor or Bluetooth headphones or would the signal have to go through an amp first?

IMHO Bluetooth should be avoided for anything musical, the latency is just too great to be useful...

Hope this sets you off on the right track!

[Tone Deaf]

Flippin' 'eck TwoTimesBass. Thank you so much for taking the time to reply with such clear and concise answers to my questions. You clearly are an expert mate, at least in comparison to me..... and a large percentage of the rest of the planetary population. For this reason you are awarded 6 OHMS !  OHHHMMMMMMMMMM.

[pete.young]

A piezo typically requires a very high impedance pre-amp. An absolute minimum of 1 MOhm, more if possible.

[TwoTimesBass]

😀 6 Ohms... I like it! Always thought of myself as a low-impedance kind of guy 😂

[Tone Deaf]

12 minutes ago, pete.young said:

A piezo typically requires a very high impedance pre-amp. An absolute minimum of 1 MOhm, more if possible.

Hey Pete Young. Thanks for taking the time to read the mini thread and contribute mate. So I'm kinda wanting to build something myself and have seen this on Instructibles. What do you reckon? I'm still thinking of connecting multiple piezos probably 3 or 5. If connected in parallel as suggested by TwoTimesBass, above, would this be appropriate then? As you are suggesting MegOhms you have been awarded 6 Ohms as well. 

[Tone Deaf]

5 minutes ago, TwoTimesBass said:

😀 6 Ohms... I like it! Always thought of myself as a low-impedance kind of guy 😂

You and me both mate.

[Tone Deaf]

If anyone's interested here's a link to the pre amp build I found. https://www.instructables.com/id/Guitar-Contact-Microphone-Preamp/

 

[TwoTimesBass]

20 minutes ago, Tone Deaf said:

If connected in parallel as suggested by TwoTimesBass, above, would this be appropriate then?

Depends on the spec of the actual piezo units you want to use. For an example of multiple piezo pickup systems have a look at https://kksound.com/products/doublebigtwin.php

[Tone Deaf]

That looks like a great piece of kit TwoTimeBass. I ordered 10 Piezos @ 20mm and 10 @ 27mm a couple of days ago. I am a total tool tart but draw the line at an oscilloscope (at the moment at least). I do have a multi-meter. Would I be able to establish the impedance of the transducers with that or is it more of a moving picture whilst the transducers are being excited by a signal? Ooo errr Mrs.

[itu]

First of all, I cannot see the need for more than one or two piezos. One/two piezos under the bridge, and that's it. If you want to use several, consider both placement and active mixing.

They can be pressed a lot (make a tiny cavity under the bridge or put one to the neckpocket), but bending kills these fragile parts easily. They are usually glued to brass disks and pre-soldered with short wires (buy these!). If your deal includes disks without wires, I would strongly suggest metal pogos or springs instead of soldering. The lead-titanate material tends to melt accidentally and soldering them is really difficult to master. Believe me, I have tried it several times in professional surroundings.

Usually FET-based preamps and opamps have so high input impedance that a piezo output is not an issue. I have found out, that the old t c electronic SCF can eat any piezo with ease. Keep the wires short, high impedance is prone to interference.

The size (diameter) affects frequency response. Very roughly a larger sensor produces more low frequencies and a smaller will be better with higher frequency content. Don't you worry 'bout a thing: your disks are pretty close in size with each other.

A reasonable impedance measuring system would be expensive.

[TwoTimesBass]

30 minutes ago, itu said:

Keep the wires short, high impedance is prone to interference.

+1 for itu's suggestion, keeping the preamp close to the transducers is good practice, and good advice in the rest of the post too.

If your piezos don't come with a spec sheet, then I guess given the amount you have coming, just experiment to your liking. The benefit of the piezos is that they are pretty robust electrically and mechanically...

I look forward to seeing/hearing what you come up with 😀

[Tone Deaf]

2 hours ago, itu said:

First of all, I cannot see the need for more than one or two piezos. One/two piezos under the bridge, and that's it. If you want to use several, consider both placement and active mixing.

They can be pressed a lot (make a tiny cavity under the bridge or put one to the neckpocket), but bending kills these fragile parts easily. They are usually glued to brass disks and pre-soldered with short wires (buy these!). If your deal includes disks without wires, I would strongly suggest metal pogos or springs instead of soldering. The lead-titanate material tends to melt accidentally and soldering them is really difficult to master. Believe me, I have tried it several times in professional surroundings.

Thank you itu. You know what it's like, you start Googling a subject and it runs away with you... it does me any way. So in short I started looking at miking up my acoustic guitars. I've come back to music after a generation away (Children and making money for the Man). I downloaded Audacity and Hydrogen to get started and just got carried away. Anyway long story short, started thinking about percussion, drums etc. and one thing lead to another and I got to thinking about something I wrote donkeys years ago.... kinda had an aquatic theme. So there's immersion at one point, and logically I guess, emersion. Anyway I hope that partially explains my fixation with piezos. I didn't fancy soldering tails to the things so I bought pre soldered with 6" tails.

[Tone Deaf]

2 hours ago, itu said:

Usually FET-based preamps and opamps have so high input impedance that a piezo output is not an issue. I have found out, that the old t c electronic SCF can eat any piezo with ease. Keep the wires short, high impedance is prone to interference.

The size (diameter) affects frequency response. Very roughly a larger sensor produces more low frequencies and a smaller will be better with higher frequency content. Don't you worry 'bout a thing: your disks are pretty close in size with each other.

FET is a type of transistor yeah? What's the difference between a preamp and an opamp and should I consider one over the other? Thanks for the advice re the diameter. I'd kinda guessed that might be the case but as you've mentioned it, I have seen 50mm piezos. Do you know why you wouldn't produce an array with say 20mm and 50mm for say an acoustic bass? would that be something to do with the phase discrepancy as mentioned by TwoTimesBass? Thanks everso much for your time itu. Fantastic advice written in a way that I can at least grasp the concepts. For your awesomeness and the way you got me to spill some guts you have ascended to the level of 7 Ohms. Nice one. Thanks mate. BTW. Did you have a look at the diagram I uploaded?

[Tone Deaf]

2 hours ago, TwoTimesBass said:

+1 for itu's suggestion, keeping the preamp close to the transducers is good practice, and good advice in the rest of the post too.

If your piezos don't come with a spec sheet, then I guess given the amount you have coming, just experiment to your liking. The benefit of the piezos is that they are pretty robust electrically and mechanically...

I look forward to seeing/hearing what you come up with 😀

Thanks TwoTimesBass. itsu is very cool and current...ly has 7 Ohhmms. If my order ever arrives (from China) I will have a lot of fun experimenting. They cost next to nothing and the applications seem, in part, only limited by ones imagination. If only I'd been more of a geek in school. Anyway, two more for sticking with it. Thanks TwoTimesBass. 

 

 

Edited July 1, 2020 by Tone Deaf

[itu]

6 hours ago, Tone Deaf said:

What's the difference between a preamp and an opamp and should I consider one over the other?

Do you know why you wouldn't produce an array with say 20mm and 50mm for say an acoustic bass? would that be something to do with the phase discrepancy as mentioned by TwoTimesBass?

Did you have a look at the diagram I uploaded?

An operational amplifier is a component inside a preamp. A preamp may be a floor box or a unit inside your instrument. Some common opamps are TL07x (x=1/2/4, depending on the "channels" within one part), NE5534, OPA-series, and so on. You have to check their specifications from their respective datasheets. It is common to do trials with different opamps, if they are pin compatible. Quite many are.

I would say that one or two disks is enough, a bigger array has phase issues and may require sophisticated mixing system. Most of the data is captured with one. Another story is if you buy a bridge with individual piezo saddles and drive each channel to a MIDI system or have other special needs. For effects like handling noises you can use several, but the mixing needs preamps for each channel. It is true there are many piezo systems with a piece of ceramic under each string and they are just in parallel. Trial and error...

I took a quick look and the circuitry is based on a FET (2N5457; these have very high input impedance by nature), and I have a hunch that this might work.

About immersion: nearly two decades ago I was a bit involved in a research project, where big piezos where studied. They were something like over 10 mm thick. Impossible to get, because they were meant for very low speed communication between submarinesor like. The result: no project output because of the costs and availability. Those were the days.

[bertbass]

Good luck with this and I'll be following it to see how successful you are.  It's a road I went down a few years ago but could never get to work properly.

[Tone Deaf]

On 02/07/2020 at 07:26, itu said:

I took a quick look and the circuitry is based on a FET (2N5457; these have very high input impedance by nature), and I have a hunch that this might work.

About immersion: nearly two decades ago I was a bit involved in a research project, where big piezos where studied. They were something like over 10 mm thick. Impossible to get, because they were meant for very low speed communication between submarinesor like. The result: no project output because of the costs and availability. Those were the days.

Hey Itu. Thanks for having a look at the circuit mate. Based on your input I feel more confident about building this. WOW I can't imagine a 10mm thick piezo actually vibrating. I love your whimsical comment.... "those were the days" If you'd care to share some memories I'd be fascinated to hear them. At this point Ohms seem almost redundant so.... one last. Thanks Ito.

On 02/07/2020 at 12:32, bertbass said:

 

 

On 02/07/2020 at 12:32, bertbass said:

Good luck with this and I'll be following it to see how successful you are.  It's a road I went down a few years ago but could never get to work properly. 

Hey bertbass. I'll keep updating once I start experimenting. Building does rely on the delivery from China of course. If you'd care to share what didn't work I'd be very grateful so I don't start down roads that might not connect (dead ends). Also any plans, circuit diagrams, observations and details of what did work would be great. 

Of course I know I'm asking a lot. Whatever you decide is great mate.

[itu]

http://www.scotthelmke.com/Mint-box-buffer.html

[bertbass]

Well, it's like this!  I wanted a quiet drum kit for recording as I thought that that was a far cheaper and better way to go.  The other way was to try and build a totally soundproofed room / shed.  Buying a Roland electronic drum kit would have been perfect but I'm a poor person so it was not to be, so I built an electronic drum kit using piezo transducers which ran into an Alesis DM5 drum module.  This worked quite well but the cymbal sounds weren't quite right and drum rolls always sounded like machine guns and I wanted each drum on a separate track whereas the DM5 only gave a stereo output.  The piezos into the DM5 worked perfectly though.

 

This brings me to plan B.  Why don't I try a real drum kit, heavily damped to make it quieter and use piezo transducers as mics.  That should solve the machine drum problem and I would sort out the cymbals later.

 

I mounted all the piezos and tried them and yes they worked but sounded terrible as I expected they would as I needed preamps for the transducers.  I built 8 preamps, infact, the circuits you posted, http://www.scotthelmke.com/Mint-box-buffer.html and excitedly connected everything up and tried it.  Didn't work very well.  Checked all the circuit boards and they were all built correctly, tried it again with the same result.  It sounded crap.

 

Here my tale ends as I gave up and went to plan C.  Put mics in all the drums then stuff them with foam to keep them quiet but due to lack of interest from others, I've still to try plan C although now we've got this virus, the others seem more keen to record.

 

I should mention that I'm not a drummer and don't play drums but I am a bass player so by extension, I'm the only one who understands these things and knows how to do them.