Piezo saddles: How can I turn on/off each string individually?

[C5DEMON]

I'm having a custom 9-string bass built and i want to have piezo saddles installed on the highest 4 strings and run to a seperate output jack. Does anyone know how i may be able to turn on and off each piezo saddle individually? I don't want to run all 4 (C-F-Bb-Eb) strings all the time, only certain strings or combinations of strings. I have contacted Graphtech and they said that you cannot just connect a switch to each. Anyone kow how this may be possible? Thanks for any help and info

Ross

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RICHTER ELECTRONIC ENGINEERING

[C5DEMON]

Thank you for the link, I think this is just what i am looking for. do you know much about it? or have you personally used it?

[line6man]

All you have to do is put a switch on each piezo output.
Make sure each element has a buffered input, however.

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I haven't tried this preamp in particular but everything Richter make is cream of the crop.

[C5DEMON]

Originally Posted by line6man

All you have to do is put a switch on each piezo output.
Make sure each element has a buffered input, however.

My luthier spoke to graphtech and they said that it is not as simple as installing a switch. I thought that's all you had to do also, but then again, I'm no electronics expert.. I'm just a bass player Have you done this or do you know someone that has? I'm trying to find all the info i can. Thanks for the help!

[line6man]

Originally Posted by C5DEMON

My luthier spoke to graphtech and they said that it is not as simple as installing a switch. I thought that's all you had to do also, but then again, I'm no electronics expert.. I'm just a bass player Have you done this or do you know someone that has? I'm trying to find all the info i can. Thanks for the help!

As long as there is a buffered input for each string's piezo, there is no reason it shouldn't work. Maybe shunt the input of the buffer to prevent noise, since the input impedance is very high.

[SGD Lutherie]

Originally Posted by line6man

As long as there is a buffered input for each string's piezo, there is no reason it shouldn't work. Maybe shunt the input of the buffer to prevent noise, since the input impedance is very high.

I think as it is all the strings are summed together in parallel? I see no reason why you can't just stick a switch in there.

A better way would be to buffer them, and then you can even pan them left and right and mix the levels.

[line6man]

Originally Posted by SGD Lutherie

I think as it is all the strings are summed together in parallel? I see no reason why you can't just stick a switch in there.

A better way would be to buffer them, and then you can even pan them left and right and mix the levels.

Well, if they are all parallel, without buffering, removing a piezo from the circuit would increase the output impedance and possibly change the tone.

[Jazz Ad]

Exactly. You need a buffer for each string.

[SGD Lutherie]

Originally Posted by line6man

Well, if they are all parallel, without buffering, removing a piezo from the circuit would increase the output impedance and possibly change the tone.

Well they are buffered, but they are all going into a single ended buffer. The piezo's are connected to a high impedance preamp. It's generally about 10M. Piezo's are not like magnetic pickups and have very high impedances. The fact that they have them in parallel shows that they wont load each other down as long as they are driving a buffer.

So I don't think it would matter much, and it worth a try. Personally I would use separate buffers, but now you are getting into a custom preamp/mixer, not that it would be that complicated to make.

[line6man]

Originally Posted by SGD Lutherie

Well they are buffered, but they are all going into a single ended buffer. The piezo's are connected to a high impedance preamp. It's generally about 10M. Piezo's are not like magnetic pickups and have very high impedances. The fact that they have them in parallel shows that they wont load each other down as long as they are driving a buffer.

So I don't think it would matter much, and it worth a try. Personally I would use separate buffers, but now you are getting into a custom preamp/mixer, not that it would be that complicated to make.

There is still a pretty large impedance change between running all piezos and only some.

For the sake of the argument, if we take four piezo elements and call each of their output impedances "1," the total output impedance can be seen as:
1 element = 1
2 elements in parallel = 0.5
3 elements in parallel = 0.333
4 elements in parallel = 0.25

Then again, I've no idea how this would translate to changes in the circuit. Piezos aren't very inductive, and it might not sound different at all. I've never experimented with this, and am too lazy for any math on a Saturday afternoon.

In any case, individual buffered inputs is the way to go. Same concept as plugging mics into a mixing console. Remove one, remove two, remove twenty, very little change in sound.

[C5DEMON]

I have not been getting much response from emails with Richter electronics but i still have a few months before my bass is finished so this still gives me time to figure this out. I am still new to piezo, so i'm getting lost in some of the tech talk, but I follow what you're saying about the impedance differences. Are any of you able to build me an onboard preamp for this idea or do you know of anyone who would build a custom piezo preamp?

[SGD Lutherie]

Originally Posted by line6man

There is still a pretty large impedance change between running all piezos and only some.

For the sake of the argument, if we take four piezo elements and call each of their output impedances "1," the total output impedance can be seen as:
1 element = 1
2 elements in parallel = 0.5
3 elements in parallel = 0.333
4 elements in parallel = 0.25

Then again, I've no idea how this would translate to changes in the circuit. Piezos aren't very inductive, and it might not sound different at all. I've never experimented with this, and am too lazy for any math on a Saturday afternoon.

In any case, individual buffered inputs is the way to go. Same concept as plugging mics into a mixing console. Remove one, remove two, remove twenty, very little change in sound.

So I had a minute to do a little searching. I remembered that when more than one piezo element is used in a bridge, like for an acoustic guitar, the elements are wired in series.

Apparently wiring them in parallel reduces the sound quality because they are loading each other down.

Piezo Film Pickups: How many can be wired together?

So this begs the question, how is this bridge wired up?

Clearly for control over individual strings, they should be separately buffered and actively summed.

It would be a fairly simple circuit to build; a JFET for each string, and then another stage to act as a mixer. Then you can use switches or pots to control each string.

[Shoewreck]

I prefer a simple common source JFET stage with a capacitor attached between drain and gate for the preamp and connect saddles in parallel.
This setup allows switching individual saddles on and off without any significant volume and tone changes, though I never used this feature.