Piezo Plate instead of Disc for pickup?

Nate74 · #1 03-05-2012, 06:00 PM

I've been messing around with a Radio Shack piezo disc and have been very pleasantly surprised at the sound I got just sliding it under a .250" thick maple bridge (very simple). It sounded good enough I'm toying with designing a bridge specifically to work with it and trying to construct something like the Realist pickup with it. Then the thought occurred to me that the Realist is rectangular and I found:

STEMINC - SMPL26W16T07111 - Piezo Ceramic Plate Voltage Generator

Has anybody tried something like this for an under bridge pickup for DB or EUB?

Paul Barsic · #2 03-06-2012, 09:14 AM

I think the Realist package is square because the bridge feet on a double bass are square. I do not know the shape of the element inside the package.

I use a square piezo element with my double bass. I sandwiched it between copper sheeting for shielding. This is the element I used:
Piezo Vibration Sensor - Large - SparkFun Electronics
I chose that one because I could put the piezo element between the bridge feet and the top table and have the electrical contacts hanging off to the side. Side-by-side comparison with a Realist showed that the realist was hotter and sounded better without adjusting the EQ on the amp, but a pre-amp and good EQ settings compensated.

Nate74 · #3 03-06-2012, 09:35 PM

Quote:

Originally Posted by Paul Barsic

I think the Realist package is square because the bridge feet on a double bass are square. I do not know the shape of the element inside the package.

I use a square piezo element with my double bass. I sandwiched it between copper sheeting for shielding. This is the element I used:
Piezo Vibration Sensor - Large - SparkFun Electronics
I chose that one because I could put the piezo element between the bridge feet and the top table and have the electrical contacts hanging off to the side. Side-by-side comparison with a Realist showed that the realist was hotter and sounded better without adjusting the EQ on the amp, but a pre-amp and good EQ settings compensated.

Outstanding insight! Thanks. I actually got a couple of these film type piezo elements from the Mouser catalog a while back. But honestly, never figured out a good way to use one. So you have this under the bridge?

Paul Barsic · #4 03-07-2012, 11:02 AM

Here are some notes on my pickup. I hope they help.

It is important to realize that the back of these piezo film tabs are conductive. If you forget this, you may get a whole lot of nothing out of your amp.

I bought the copper from a place that sells craft supplies. I bought a sampler pack of 6"x6" copper sheets of varying thicknesses.

Attached is a picture of my pickup. There are two pickups in the photo, one is clamped in the bridge wings and the other is under the bridge foot. I preferred the sound under the bridge foot, so the one on the wings is gone. The Realist has the fat roll under the bridge foot rather than the side, which is a better design because it makes it easier to verify that the bridge feet are in line after making bridge adjustments. If I were to do it again, I would copy this feature of the Realist.

Here are things that I did. Some of them will be irrelevant to you.
1. I encased the signal wire in fabric by taking a shoelace, cutting off both ends, and working the cable through it. The piezo element will pick up taps on the cable, the fabric will reduce this.

2. I slipped grommets (from a hardware store) around the barrel of the jack to keep it from making clicking noises on the tailpiece. It was held in with a Velcro cable tie, while now it is held in with a zip tie, sits behind the tailpiece, and is oriented horizontally rather than vertically.

3. There is a loop in the cable so that the slack in the cable does not knock against the bass. The loop is held in place with another grommet.

4. For stability, there is a stiff wire soldered to the foil and going into the first 1/2" of the cable sheath.

5. There is heat shrink tubing around the cable sheath at the top to prevent fraying and to provide an anchor for the stiff wire.

6. The copper shielding is grounded.

7. The copper foil shielding is held closed by a dot of super glue. This is because using the bridge height adjusters causes some torque on the feet and the shielding will slip against the piezo. I tried to keep it off the piezo tab since some plastics are degraded by super glue.

Nate74 · #5 03-07-2012, 06:17 PM

Good info Paul. Thanks. I may get some time at the work bench in the next couple days so will mess around with the piezo film tab. The discs seem to be a dead end when it comes to under saddle designs...

Paul Barsic · #6 03-08-2012, 08:19 AM

I'm glad I could help. Let me know what you end up doing.

I did this two years ago, and _nobody_ has been interested in it, so I appreciate the opportunity to blather on about it.

I also have a Stagg EUB, and they use a piezo wire, like this one:
Piezo Coax
They put a channel in the underside of the bridge feet to seat the cable. This kind of piezo is also used for some acoustic guitar pickups. If the tabs don't work for you, this is yet another option.

Paul Barsic · #7 03-08-2012, 08:22 AM

This is another good source for parts: Electronic Hardware

Nate74 · #8 03-08-2012, 09:02 PM

Paul - this is actually a two part project. I did my first EUB build about two years ago and only recently got the pickup worked out but I'm still tinkering. I ended up using an "under saddle" pickup and this bridge design:

It works well but really has no acoustic sound to it. I'm OK with it but thought maybe I could find a way to use a design under a bridge foot, but the discs get smooshed and stop working pretty quickly.

My latest built will use a 1/2 DB bridge so I'm hoping it will vibrate enough to open up some other options, like one under a bridge foot etc.