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Latest on Piezos
- Thread starter Mickey666
- Start date
First, there's a lot of misinformation that's parroted about exactly what piezos are (or aren't...) and how they are best used in musical instrument applications. First, the no load voltage generated by the average pickup can be extremely high. That's the main reason they produce distortion at minimal gain levels if the preamp isn't designed to accommodate them.
In the right application piezos can be used successfully without the need of a pre-amp for impedance matching. K&K has sold boatloads of piezo guitar pickups and they can be used without impedance matching if they are directly feeding an amplifier with a 1 megohm or higher input specification. I have several acoustic guitars with K&K Pure Mini pickups that work fine with the amps I have available. Bonding to the bridge plate is critical, because the transducers work best in bending mode, as previously suggested.
Piezo transducers are rated as multi-megohm impedance elements and that physical specification combines with what little capacitance is present in the average guitar cable to make an efficient high pass filter, often contributing to the brittle high end tone they are faulted with producing. It helps to use a quality low capacitance 1/4" cable to minimize the effect on the resulting tone.
Manufacturers have known about the "filter problem" for a long time and Baggs and other preamp manufacturers suggest that the transducer to preamp connection be kept as short as possible, 6" or less being the ideal. Those details are why you find piezo undersaddle pickups often combined with a preamp that is mounted internally in the instrument.
You might be interested in a build I detailed (HERE) on Talkbass that uses a Baggs Element undersaddle transducer and end pin preamp. These are often taken out of brand new guitars and sold on the used market. I've bought 4 of them at $50 or less. They actually work well for bass, and the volume and tone controls can be simply be clipped off if running directly to a jack.
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That’s the Ghost system and I believe it’s been suggested. It works pretty well and I suppose you could figure out where you want the knobs set and add trimpots or fixed resistors instead of full size pots.
I like @Lo-E’s suggestion of checking out what the DB guys are using or, if you’re using and acoustic guitar type bridge, what those guys are using. I had a friend who played acoustic with a system that was passive on the guitar and went through a phantom or battery powered pedal and sounded really good. Can’t remember what it was though.
@Marc DLarosa looking forward to seeing pictures of the paisleyness when you’re done.
This bass sounds great. I didn’t build it, Cliff Bordwell built it for me. Piezo in the bridge. Fretless semihollow with tapes. Richter preamp on board.
Most piezo transducers have a resonance somewhere - often it's above 20 kHz - a lot of acoustic guitar pickups resonate somewhere around 40 to 50 kHz. While you think that'd be OK, it turns out that that resonance will mess with some wireless units (including the ones I worked on), which either use tones up there to know that it's one of your transmitters, or listen for signals in that frequency range to assess signal to noise, and determine when the signal is poor enough that it should be muted. So, a circuit I came up with, that I thought was genius, and that worked great in lots of applications, would mute the signal when someone hit a chord on an acoustic hard. We had to filter that signal out in the transmitter, so the receiver could behave properly.
One other practical issue with piezos is that they respond to pressure (changes in pressure become the signal), and if the interface between the bridge on an acoustic instrument and the wood beneath it isn't dead flat, you can end up with certain strings that are much softer than others - they aren't directly putting pressure on the piezo transducer. On fix for this is to cut the bridge saddle into several pieces - each string having it's own short saddle. Doing that, you guarantee that every string will push on the piezo, so the problem goes away. Of course, when you change strings, now you have 6 small bridge saddlettes to keep track of, rather than one long bridge saddle.
And yes, piezos need a high input impedance to have decent low end. If you have on onboard preamp, it does that for you. The Countryman Type 85 DI box has a 10 Megohm input impedance (much higher than most DI boxes) - it works fine with piezos that don't have a preamp on board. Every good sound guy/venue should have at least on of those on hand. I did have a band show up once that told me I had to mic their acoustic. I remarked that it had a pickup. They said it wouldn't work. I told them I had a DI that would. They told me "everyone tells them that". I said "humor me". It worked just fine.
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Piezo transducers are capacitive sources. They need a high impedance load to avoid rolling off low end, but loading a capacitive source (a piezo) with a cable (a capacitive load) DOES NOT result in a high pass filter - it forms a voltage divider, which means the cable attenuates the signal evenly across all frequencies - it makes it quieter, it does not change the sound. So, a low capacitance cable is useful, because it preserves signal level, not quality.
An acoustic instrument's wood top is an acoustical low pass filter - what radiates to the air is a "rolled off" signal. The reason the output of a piezo often sounds brittle is because it is NOT rolled off - it picks up vibrations that have not been filtered acoustically. If you want your amplified acoustic to sound like it does acoustically, a single pole filter rolling stuff off above about 3 or 4 kHz usually gets you in the ballpark of where you need to be.
I am not aware of any new piezo developments so things from 10 years ago are probably still valid -- or at least as valid as they ever were
In case you haven't read enough, here are some basics of piezo pickups:
Magnetic pickups are mostly inductive while piezo pickups are mostly capacitive. Without getting into the details, that basically means they work opposite from each other in many ways. The signal generated by a piezo is also pretty small which, combined with a typical bass preamp input impedance, means that they don't work that well with piezo pickups.
Being inductive means that magnetic pickups become low pass filters when loaded, while piezo pickups become high pass filters, making them sound thin in typical bass applications. A very high impedance buffer on the piezo will help preserve the low frequency response and normalize the level relative to magnetic pickups, but they you need to worry about how and where to put that buffer.
Anyway, ask more questions if you still have them and good luck!
The conclusions are mostly correct - but - just to be factual -
Piezos are mechanical - not capacitive. They are a tiny crystal that is vibrated by the string's motion that generates electricity. By their nature, they are very high impedance, higher than a typical guitar amp input, so the voltage level gets sucked down if connected directly, and the capacitance of the cable affects the sound as well. You want the input impedance to be typically 10x the load impedance. That is why a preamp with a VERY high input impedance of some kind is necessary for correct operation that has a low output impedance to drive the cable, etc.
Be aware that since the piezo picks up every little movement and has a wide frequency response, they also pick up finger noise very well.
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I love that you responded to @Jeff Siddall about electronics as though he was a noob.
My NS Design CR5 Radius basses have piezos as well as magnetic pickups. While I find that generally, the piezos are a little too "zingy" for my tastes, Ned Steinberger was kind enough to include a switch that cuts or boosts highs from the piezo circuit. With the high cut engaged, I find them to be a bit more usable, but honestly it's more of a novelty than anything else. My ear wants the magnetic pickups and the way they sit in the mix. Additionally there is a blend between magnetic and piezo - which ends up presenting a large number of tonal options. Even so, I tend to keep the knob spun toward 100% magnetic most of the time.
Overall it's a nice feature to have, but my personal needs haven't found much of a use for it.
Overall it's a nice feature to have, but my personal needs haven't found much of a use for it.
Not much to say except that I have Ghost piezo
in my Stambaugh with one Aero mag PU that needed a buffer.
Piezo has huge bass and very bright highs that I tame as a preference.
in my Stambaugh with one Aero mag PU that needed a buffer.
Piezo has huge bass and very bright highs that I tame as a preference.
In one direction,Piezo’s turn vibrations into electricity (pickups).
In the other direction, Piezo’s turn electric energy into sound (tweeters).
Piezo-electric devices are used in industrial devices that have nothing to do with audio- sensors, vibration damping…..
In the other direction, Piezo’s turn electric energy into sound (tweeters).
Piezo-electric devices are used in industrial devices that have nothing to do with audio- sensors, vibration damping…..
Lots of great information folks, thanks
I'll have to do some more thinking...
I may just have to change my original plans and go with mags... just because I want to play this thing before I lose the ability
I'll have to do some more thinking...
I may just have to change my original plans and go with mags... just because I want to play this thing before I lose the ability
If you're looking for someone who does this in CONUSA, Wendler does...
MagPi | Guitar Repair Kansas City | Luthier Acoustic Electric Guitar
Check out Schatten Electronics as they produce a very small inexpensive buffer you could use onboard before sending the signal to an amp. It would need a battery but not any volume or tone, just an output jack. I have one for a replacement in an earlier piece five string but haven’t had a chance to install and test.
Will do. Although... there's been a small change in plans. I decided to go with a Jazzmaster body. WOO HOO!!!
Interesting information, except it is incorrect. Bassamatic's reply provides the factual information relating to piezo transducers.
Piezo "pickups" as represented by the type we find in undersaddle transducers or soundboard transducers are not "capacitive OR inductive", although advanced transducers used in various industrial applications combine capacitive or inductive elements within the entire "sensor".
The type of transducer we associate with instruments is simply a "piezoelectric" material sandwiched between conductive materials that serve as electrical connection points. Piezoelectric material can take many forms from something as simple as a quartz crystal to one of the MANY ceramic or polymeric materials such as lead zirconate titanate. (Yes, I had to look up a list, as these aren't in my common vocabulary...) Even a cursory check of eBay for piezo disks will reveal some of the various materials used in the manufacture of "simple piezoelectric disks".
All of these materials do exhibit high "resistance" to the ability of a current to flow through it, but since it isn't strictly a conductor or insulator that resistance is normally referred to as "impedance".
All of these materials basically work by producing actual voltage then they are "moved" even a TINY bit. The effect is VERY efficient, and it's the exact same process that creates a visible spark across a gap in your two buck barbecue lighter.
Sorry, no "capacitance" involved in the process.
