Piezo pickup question

[bluemonk]

I'm tweaking with my archtop and cheap disk-shape piezo pickups (inspired by K&K Pure Archtop). These piezos have decent output level but of course are harsh. Running them thru a preamp doesn't help
Got a good tone with a 10k resistor in series and a .047 cap in parallel. Is there something wrong doing that? (Apart from a lower output level?).
Thanks in advance.

[Mark Hammer]

Preamp needs to have a fairly high input impedance. Not just any preamp will do, but I suppose you probably already knew that.

There is also the matter of where you put them, the size of the disc (bigger disc, lower resonances), and what you affix them with (some adhesives will damp mechanical coupling and reduce bandwidth).

Failing that, you can always consider inserting a gentle broad passive mid-scoop in the preamp circuit to lend some tonal balance.

[bluemonk]

Yes, I tried a DIY preamp (www.dogstar.dantimax.dk/tubestuf/instpre.htm) and a Barcus Berry piezo-preamp. Piezo disk is 1 inch large.
"Passive mid-scoop": how to do it?

Experimenting with passive components I damped the harshness and got a better tone by adding a resistor in series and a cap in parallel. It lower overall output but seems to work. I wonder why nobody mention this kind of arrangement. Is there something wrong?

Thanks

[David Schwab]

That tube preamp looks much too complicated for what you need... it's surly altering the sound of the piezo. Also with the tone controls in that preamp yuou should be able to roll off the highs and scoop the mids if you need it.

I'd try a simple FET buffer first to see if that doesn't fix the problem.

[bluemonk]

I did try a Barcus-Berry piezo-preamp but doesn't seem to solve the problem.
Regards

[Guitarist]

Well this seems to be one of the most basic (see att.).

I'm wondering how to power this from a mixer's 48V phantom power via the 3 way/XLR cable to the guitar's 1/4 larger Switchcraft right angle that's currently housing the fet and 3 resistors.

A lot of sites posters say easily adapted to phantom power but nobody elaborates. Max 40V allowed to a J201. Sure would be nice to opt out of the 9V box.

[Guitarist]

Well I get to answer myself: I got the phantom thing to work great- as a first try anyways. I converted the dumbed down mic cable back to full and took the - pin wire and added a voltage dropping resistor I think 33K or so. The + comes off the "plate" and shield gets ground. I'll try and draw up a schematic. I used a 10Meg input resistor.

I have to say it sounds amazing will all the following: especiallly with B-Band element in a dreadnaught (slight hiss and req. 100% shielding or faint hum),

3 daisey chained piezo disks (no hiss or hum even totally unshielded) in a Framus classical (could use some flattering eq),

and using an electric (so versatile: acoustic sim. at the best I've heard).

All were simply heard with phones into a mixer with and without reverb/delay.

This seems to be one of those significant wraps for me personally and I'm really impressed with these new, HIGH quality tones. A fun a satisfyin project.