piezofilm pickup for electric upright bass

[Lovelock]

Hello All,

I am completing a solidbody electric upright bass, and obtained piezo film material.
Want to make pickups to fit in bridge slots "a la underwood". Would like some construction tips & feedback on my ideas here.

I have no questions regarding shielding, short cables or high impedance preamps.

What I am wondering about is the following: Should I use the material flat so it just compresses through (it's very minimal) thickness with vibrations,
or would it be a good idea to mount it ever so slightly curved over a piece of flexible material (thin solid neoprene?) so as to make it bend more with vibrations?

I will experiment, and will post my findings, but am just wondering if there are any thoughts or other ideas that will help make a better pickup.

[copperheadroads]

certainly interesting keep us informed

[Rick Turner]

I prefer piezo ceramic blocks for my URB pickups.

That said, it's all about location, location, location and geometry, geometry, geometry. The specific technology is far less important. Of course, the next issue will be buffering/preamping, how much or little gain you will require, and the fine tuning of the input impedance of your preamp to get the right low frequency response without getting too much of the sub-sonic "below the music" stuff.

I'm not going to tell you how I design my piezo pickups. They work to MY requirements. Design your own, but know the above important design parameters. Then do your own work and come up with your own signature pickup design.

[Lovelock]

Thanks for the helpfull advice Rick. I never expected a "just add water" recipe for piezo heaven here. I am not in the pickup business, and used to be quite happy mounting Ashworth pickups on the few bowed instruments I built. But since Alun Jones sadly passed away, these pickups are no longer made.
That's why I am now experimenting to make my own for this instrument. I have experimented with block ceramics quite a lot, but never tried piezofilm.
That's the reason for posting this tread.

Today I did the first experiment. I mounted a piece of film on a very thin piece of synthetic rubber with a very slight radius to it (as to make the pickup bend more when compressed). I shielded top & bottom with copper tape to keep the noise down and mounted it in the bass side wingslot of an acoustic upright.

The output of this pickup is far lower than with ceramic block types, so I had to use a preamp to get a healthy signal. I was expecting this, so last week I cooked up a first proto preamp (two cascading jfet stages with a volume inbetween and 10M input). I will change the input and add some dipswitches to play with the input impedance as Rick Turner suggested.

I was worried about the high end not getting through because of the dampening effect of the rubber, but the sound was actually quite usefull. It wasn't harsh either. It really needed the preamp though. If plugged straight into a Schertler Unico there was a definitive lack of low end and a very poor signal.
I'll construct a similar pickup on a flat piece of rubber next and then compare the two. I'll post my findings when I do so.

In the meantime I'll welcome any suggestions or thoughts for further experiments concerning piezofilm.