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Permalink Reply by David McQueen on May 17, 2013 at 3:15pm

You would probably get better match using a preamp on the piezo. You would also be able to use a common tone control. A raw piezo needs some special,treatment to use a passive tone control and cannot use the same control as a standard pickup.

One thing to watch. i have been playing with building my own preamps this winter. So I have been looking at the preamp designs. Most of the simple designs using JFET's (field effect transistors) invert the signal. You specifically need a preamp that won't do that if you want to mix the pickups. For a JFET preamp that would mean it has to be a two stage amp. Not sure what would be required with the ones using an integrated amp circuit or mixed JFET buffer and an IC preamp.

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Permalink Reply by Kevin (Voodoo Rat) Hoelting on May 19, 2013 at 7:57am

Wow, thanks David. The inverted signal, and the signal cancellation I am assuming would result is EXACTLY the type of headache I was talking about.

I actually have a CBG that is my crash test dummy. The back opens up and the poor thing has had more wires run through, and cut out of it, than a medium sized arcraft. On a whim, I hooked up an old pup from a mexican strat, and a disc piezo. Two circuits, two jacks, two cords, run into the two channels of a fender hotrod amp. I kind of matched the levels up with the volume pots.

And the verdict is...........................

Mehhh. I mean I could tell what was going on, but it wasn't the sonic revelation I was hoping for. On a resonator, I believe the tone would be worth pursuing. Nothing cries like steel, but I think I will shelve the idea for a cold, rainy winter day.

Thanks a ton for your time and thoughts.

 

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Permalink Reply by David McQueen on May 19, 2013 at 8:39am

You need the preamp. Discs are actually good pickups, but the impedance is far too high. Here is a link to the simplest one I have found. It is really high impedance input and it is pretty much silent.

http://personalpages.tds.net/~fdeck/bass/quickand.pdf

I added a couple,of 5.6 v zener diodes just past R3 for protection.

I think two of these back to back might give you exactly what you want. A high impedance, zero gain preamp with double signal inversion. You would have to experiment.

I go out and play once a week. I have a 6 string cbg with dual pickups. One is a single piezo disc at the bridge and the other is a 3 disc piezo belt in parallel by the neck. I am using pots that actually have an off setting so I can definitely use one or the other or mix them. I have been able to mix and match running both through the preamp and then a small bass amp such that I am getting comments that the spund is really good.

I also tried a passive tone control on a 500 k-ohm pot. I can hear some difference, but not enough to make it a successful experiment that way. Another thread talked about using megaohm pots, which sounds like it might be the way to go if one is going to have the preamp as an external box.

So the short story is a raw piezo is a really affordable pickup, but with some more work, it can be more than that.

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Permalink Reply by Kevin (Voodoo Rat) Hoelting on May 29, 2013 at 2:05am

Hey thanks Dave. Sorry for the delay in responding.

You don't have to sell me on piezos. I LOVE the things. Thanks for sharing your knowledge on the little critters.

The main reason I was wanting to do something like this is that I am not quite ready to "evolve" to rod piezos and mag pickups. There is too much sonic mojo that they simply miss. That, and I have a bag of 20mms that I am not about to waste.

Thanks for sharing the plans. The parts are on the way to build 5 of them. I like the idea of everything being onboard. It builds the mystique of "all that sound coming out of that little box".

Thanks again, and have a great day. I will keep you posted.

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Permalink Reply by David McQueen on May 29, 2013 at 2:55am

One thing I missed and will probably try.  With the CBG with two disc pickups, by mixing t6he volumes I am getting a real tone difference. I am going to look into a volume blend.  That may be the way to do passive tone on a Piezo - Bridge and neck discs of different sizes with a blend pot....All through a preamp.

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Permalink Reply by Wade on May 30, 2013 at 3:06pm

I've had good results taking a preamp that would go into an acoustic guitar and with a simple mod make it an external preamp by putting it in a small cigar box. This way you can use it on all your builds.

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Permalink Reply by David McQueen on May 30, 2013 at 11:14pm

That is actually what I did with the preamp with the schematic link posted above. I inserted a switch instead of switching through the jack and put the zener diods as described above for static protection.

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