Piezo Questions

[killemall8]

I have wanted to do a guitar with a piezo for quite some time. After Pan kara did his nylon string guitar with it, it reallyk got me excited to do it.

But the thing is, i am completely clueless about them. I dont get how they work, or what i need for them.

I see the ghost saddles are the most popular. Stew mac sells them. But on top of that, i am guessing i need a preamp and all that?

Fill me in a bit. I just spent like 25 minutes going through every single thread that had to do with piezos, but i am still lost.

I found this one, built in to the bridge:

http://www.ebay.com/itm/Black-Nickel-Piezo-Tuneomatic-Bridge-ARB-Style-Bridge-Fits-Import-Lp-Guitars-/370802376247?pt=Guitar_Accessories&hash=item56558b3e37

How does that one work, when it only has 2 wires?

[pan_kara]

I'm not an expert but since I seem to be the guilty one here let me answer

What we call "piezo" is basically systems that exploit the piezoelectric effect, where voltage is generated through mechanical stress (pressure) in a piezo crystal. so basically you put this material under the saddle and as the string causes the saddle to vibrate, this gets picked up and translated into alternating current. So this is independent of the sting material, and on the other hand it will pick up things like knocking on the saddles etc.

Its best used with a preamp, the graphtech system has one, they call it the "acousti-phonic", but that's not the only option, I have a Mayones 7-string that has graphtech saddles, but they are using some preamp they designed themselves. The graphtech one lets you mix between the piezo and magnetic pickups (which of course wasnt needed in my case)

The reason the graphtech system has 6 cables is that it doubles as a hexaphonic midi system if you add some additional hardware, so you have separate signal from each string. But thats not necessary in general, typically electroacoustic guitars have a single piezo "pickup" under the saddle with just a pair of wires running to the preamp, and that is probably the case for the one you link.

Back in the 80's my brother had a really cheap acoustic guitar and he bough for next-to-nothing a small "piezo kit" which was a coin-sized thing that you attached with some sort or wax-resembling substance to the soundboard of the guitar, plugged a jack and played. No preamp. The tone was different depending on where on the soundboard you attached the thing.

hope this helps!

[ScottR]

K-

This one went in the Hook Custom I built a few years back along with the powerchip preamp.

http://www.fishman.com/products/view/tune-o-matic-powerbridge-pickup-1

Skullsessions has been happy with it.

SR

[dpm99]

It's hard to get information on this topic, but it boils down to this. You're going to at least need a piezo buffer if you want to blend in magnetic pickups. A preamp is better, and you're unlikely to get the sound you want without a preamp. For the piezo pickup itself, you can get those piezo saddles, and I think they're pretty good. But I think it was Pete that several years ago took the element out of a Radio Shack piezo buzzer and stuck it on the tremolo block of a Strat. Supposedly, the results were pretty good.

[killemall8]

Thanks for the replies guys.

I am contemplating making a guitar that will only have a a piezo. Are there schematics for the preamps and the piezos out there?

Scott,

That would work perfect, but i want it anything but chrome colored.

[ScottR]

The one I used was gold. I don't know what else was offered. Hook bought that one and had previous experience with Fishman. I'm pretty sure I saw some schematics on that website.....

SR

[killemall8]

The one I used was gold. I don't know what else was offered. Hook bought that one and had previous experience with Fishman. I'm pretty sure I saw some schematics on that website.....

SR

Now that i look at it, i am definitely not paying 200 bucks for it.

There have got to be some cheaper options!

[dpm99]

It is gonna be an Explorer-type? It sounds like you're trying to build something to stand in the place of an acoustic guitar. Am I right?

There are many, many cheaper options. I'm sure that bridge you linked to is fine. I'm of the opinion that with these piezo bridges, it's more about how the sound is processed than how the sound is originated, but that may just be me. If you need a lo-pro solution, here's one:

http://www.guitarfuel.com/Acoustic_Preamp.php

I have one of these in a drawer waiting to be installed, so I can't give a real review, but other products I've ordered from that company have been great.

[Ripthorn]

I really like piezos myself. So here goes a little bit of info.

The way a piezo works is that you have a piezoelectric element, which can be a crystal, a film, etc. The way these work is that their crystaline lattice structure is such that when they vibrate, they create a very small electrical signal. The two wires that come off of most piezo elements are simply the + and - of this signal, like a single coil pickup. However, because of how the signal is created, they have an incredibly high output impedance. The reason they sound thin and weak into an amplifier (or mixed with magnetic pickups and then into an amplifier) is that, although your amp has a very high input impedance relative to your magnetic pickups, it doesn't look so big to your piezo. This in turn results in an impedance mismatch which means that some of your signal is converted into reactive impedance which is essentially signal loss. It tends to be the lower frequencies that go first, thus the harsh sound and thus the need to buffer the signal.

As far as why you only see two wires, they tend to use either a single element or individual elements that get wired in parallel so that you have an easier wiring job. If you go with something like the ghost saddles, you can do all kinds of cool stuff from an effects point of view, but it is much more complicated.

Now for preamps/buffers. A preamp is simply a buffer that has some sort of tone shaping to it. It can be simple or complex. A buffer, strictly speaking, is just an opamp or transistor that has (in our case) a very high input impedance and a low output impedance. This makes the guitar amp's input impedance look big again, so there is no (or very little) signal degradation. The DIY design that I really like and have in my bass is the PZP-1 from Cafe Walter. It is simple to do, has a relatively low parts count, and sounds good. The only thing is that I wired up the output pot as a typical volume pot instead of a variable resistor. I did this because the output was too hot relative to the magnetics I was blending them with. I can now turn the volume down so that there is no spike in volume as I go from all magnetic to all piezo. Piezos and magnetics on blend pots sound amazing.

As for commercial units, they all basically consist of a buffer and some tone shaping. Of course, cheaper ones use cheaper components which may not hold spec terribly well. But if you build one yourself, you should be able to get something really good for cheap. I think mine cost $2-4 for the materials and took about 30 min to put together, and that was well before my effects building days, so I had basically no experience.

[Workingman]

I have been experimenting with piezos for upright bass pickups for the last several months. There are a few things to be aware of. The ceramic crystal piezos degrade over time. On upright bass pickups they tend to last around five years but can go bad in as little as six months. This is an inherent part of the crystals. If you are going to use them, make sure they are replaceable. An upright bass does subject them to a lot more pressure so I don't know how they would last on a guitar.

As Dpm 99 said, you need somthing to bring the output from the piezo in line with that of a magnetic pup if you are going to use the guitar with a standard guitar amp. Some amps designed for acoustic instruments have dedicated piezo inputs. A pre-amp is best and one suing a simple op-amp circuit will work fine.

Piezos are cheap and you could buy a few different kinds and experiment. Most piezos are very prone to picking up rf interferance and 60 cycle hum. They make a Strat pup seem like the best HB ever. Some form of shielding is nesccasary.

[ScottR]

Check out johnnyforeigner's first build. It seems like he made a very simple and cheap piezo setup that worked with his TOM.

SR

[Workingman]

Prompted by this thread I tried on of my upright bass piezo setups, installing under a Fender style bass bridge. It worked fine but still sounded pretty much like an electric bass. There was some attenuation of the highs but otherwise no big idfference.

[dpm99]

Prompted by this thread I tried on of my upright bass piezo setups, installing under a Fender style bass bridge. It worked fine but still sounded pretty much like an electric bass. There was some attenuation of the highs but otherwise no big idfference.

Wait... I'm sorry. You hollowed out a spot underneath the bridge on a solid body electric bass and affixed a piezo to the bottom of the bridge? I've heard of people doing stuff like that before.

You say it sounded like an electric bass. Did it sound good?

[Prostheta]

There's no reason it wouldn't work David. Think about undersaddle or even acoustic soundboard transducers. A transducer attached to the headstock stills "hears" the instrument playing hence clip-on tuners. This would be more or less unusable as audio however and only serves as an extreme but real example. Piezos and electrets reproduce the physical resonances in the instrument which affect the transducer rather than reading one part indirectly; metal string mass moving through magnetic fields. Given that a bridge as a unit couples the endpoints of the strings to the body, putting a transducer under the plate puts it slap bang in the point from where frequencies propagate through to the instrument. It does open up interesting ideas such as "what would one sound like in the pocket of a bolt-on?" for example. Excellent fodder for messing with the heads of set/through neck purists.

I've also been thinking about integrating an electret (a B-Band UST - a good alternative to piezos) under the saddle of an archtop bass to complement the magnetics and add more of that acoustic element back in. The idea has been there for a while. Pankara's demo video just blew me away and made it a must-have rather than a mere option.

Ripthorn said it all quite admirably about pre-amps and their importance in piezo/electret circuits. If you go hunting around for candidate circuits, I highly recommend those with FET (field effect transistor) input stages. These present a phenomenally high input impedance to the transducers and give you more honest reproduction. I can't imagine many people wouldn't use them to be honest. If you want to go with a chip-based op-amp with FET input stages rather than soldering in canned trannies, my favourites are things like the OPA2017:

http://www.ti.com/product/opa2107

TI will happily send you 3 samples FOC.

Most op-amps will work well however ensuring they are stable at unity gain is a must since you are building a buffer. Joel's/Cycfi's thread and his blog are good places to get good information on chip hunting. I defer to his judgement in these matters.

[Workingman]

dpm99, what I used was a piezo film (much thinner than piezo crystals that most people are aware of). I didn't have to hollow anything out. Sonicly it sounded like an electric bass, not an upright bass or an acoutic bass guitar. It wan't bad but I don't think it would be worth the effort of a permanent installaion.

[Prostheta]

Nice proof of concept though. Since I am moving more towards learning the ins and outs of archtops and acoustics the methods of amplifying these usefully is a subject I have a lot of interest in. What kind of piezo film was it? Kind of like the thin heart monitor films?

[Workingman]

Nice proof of concept though. Since I am moving more towards learning the ins and outs of archtops and acoustics the methods of amplifying these usefully is a subject I have a lot of interest in. What kind of piezo film was it? Kind of like the thin heart monitor films?

I am not familiar with the heart monitor film. What I am using is about 2cm X 1cm by about 4ml thick. The problem is piezos are very prone to picking up RF and other electrical noise. They have to be shilded. If you are puting them under a bridge, the top of the bridge should shield and you could put some copper tape underneath. The wire could run through the ground wire hole. A pre-amp while not absulutly neccassary, is a big help.