Optimizing standard guitar effects for use with passive piezos?

[no one ever]

A violinist friend of mine is using my OC-2 for a great intro to a song; but the overall level is too low for the effect to be easily used. Any ideas?

[Paul Perry (Frostwave)]

The trouble with passive piezos, is the huge impedance (which means even a tiny amount of cable will suck an astonishing amount of signal, esp. highs).
What does the violin pickup normally run into?? That will give an indication of what you need.
Unless you are going to build something specially, I'd be looking at a small preamp/mixer & put the FX after it, or in a loop.

[R.G.]

Piezos have high source impedance and also high output levels in general.

Don't most piezos have on-board buffers to allay some of the problems with then driving cables?

A small JFET preamp or JFET-input opamp on the violin would be the ticket. You might have to buffer and either amplify or pad down the signal. Be ready for either one. I wouldn't use a piezo with a buffer having an input impedance less than 1M.

[George Giblet]

I'm with Paul and RG.

Checkout part 3:
http://music.calarts.edu/~chung/gear/vioamp1.html
http://music.calarts.edu/~chung/gear/vioamp2.html
http://music.calarts.edu/~chung/gear/vioamp3.html

Checkout the manuals/specs for Fishman PRO EQ II and the LRBaggs
They both quote the ubiquitous 10MEG input impedance for piezo preamps.

I seem to recall the Piezo compatible SWR amplifiers had 3.9MEG input impedance.

A JFET preamp would be the first choice.  A preamp using JFET input opamps would be next.
I wouldn't use a MOSFET, regardless of input impredance, because the input capacitance is too high.
Avoid adding caps to ground for RF purposes at the input of the preamp.

Place the preamp near the instrument, no long leads, good shielding.

[syndromet]

I used this on my piezo equiped guitar, and it sounds great! Helped the sound a lot. I'we also gotten mail from another guy trying this with his mandolin with great results.

[no one ever]

now I have to think of where to mount the thing on the violin...

[syndromet]

This kind of circuit is amall enough to slip in the f-holes of a violin. If it already has a jack output, I guess you could just substitute it with a stereo-jack, and provide power through the ring of a stero-cable from a stompbox. The preamp should be placed as close to the piezo as possible. Is it a "bridge"-mounted piezo transducer? Are the wires internal or external?

[Eb7+9]

give the Boss TU-2 tuner a try - it interfaces well with many Piezo's even though Zin is "only" 1Meg

[Satch12879]

I used this on my piezo equiped guitar, and it sounds great! Helped the sound a lot. I'we also gotten mail from another guy trying this with his mandolin with great results.

Um, I'd check this layout because it's got the input grounded by the 1M going into the source of the J201 where it should be going to the gate.  It also seems to have a jumper connecting the V+ to the output...

[bwanasonic]

Um, I'd check this layout because it's got the input grounded by the 1M going into the source of the J201 where it should be going to the gate.  It also seems to have a jumper connecting the V+ to the output...

That original schematic shows wires crossing without a *node dot*, which can be very misleading.

Kerry M

[syndromet]

I used this on my piezo equiped guitar, and it sounds great! Helped the sound a lot. I'we also gotten mail from another guy trying this with his mandolin with great results.

Um, I'd check this layout because it's got the input grounded by the 1M going into the source of the J201 where it should be going to the gate.  It also seems to have a jumper connecting the V+ to the output...

You are right. When I look at it now, I see that this is my first layout, wich I corrected later on. Now I can't seem to find the revisited version, but that cap is a filter cap for 9+, and should go from 9+ to ground...

EDIT:: I found my correct layout!! The link futher up is updated, and so is my webpage. ::EDIT

BigMan posted a layout for this one at http://aronnelson.com/gallery/TheBigMan-Layouts/preamphere, so I guess you should use this one instead. From what I can tell, he has not included the power-filter cap in question.

EDIT:: I found my correct layout!! The link futher up is updated, and so is my webpage. ::EDIT