Yes this completely works, I can't tell the difference in a listening test. I didn't realize I could use the capacitance of the films this way... but on the datasheet for the films, it does say "AC Coupled"... now it makes sense.
So the added resistors are to protect the transistor and the opAmp against experiments gone foul? I've used 1K resistors... would something even smaller like 10 ohms work? (my reasoning here is to affect the audio the least amount, while still protecting the components... but maybe I'm thinking of resistors too much as if they were fuses... I'm not sure)
So the added resistors are to protect the transistor and the opAmp against experiments gone foul? I've used 1K resistors... would something even smaller like 10 ohms work?
only a design suggestion.......personally preferred: res in the K - ohm dimension (1K or sowhat)..........against hf problems (e. g. the res gives with the input (gate) capacitance a small filter.........).
only a design suggestion.......personally preferred: res in the K - ohm dimension (1K or sowhat)..........against hf problems (e. g. the res gives with the input (gate) capacitance a small filter.........).
[QUOTE Any opinions on the output cap? It's 10uF, so as far as I know, this will be have to be an electrolytic cap (due to the high value, and the fact that I don't have too much space in the guitar cavity to work with)....
you can bend the leads of the "radial" cap "rectangular",so it lays down on the pcb - or use axial electrolytic's.......
you can bend the leads of the "radial" cap "rectangular",so it lays down on the pcb - or use axial electrolytic's.......
annother example: if there is not enough space around,perhaps you can build in a smaller electrolytic:
if the input impedance of your soundcard is in the 10K - region,the output cap "will see " a load around 5K (10K pot parallel 10K ).
with 10uF this gives you a cutoff freq. near by 3 Hz........
with 4,7uF you get 7 Hz......
and 2,2uF is around 16 Hz.
if the input impedance of your soundcard is in the 10K - region,the output cap "will see " a load around 5K (10K pot parallel 10K ).
with 10uF this gives you a cutoff freq. near by 3 Hz........
with 4,7uF you get 7 Hz......
and 2,2uF is around 16 Hz.
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so... I'm doing some tests... unsuccessfully thus far.... trying a circuit for each piezo. Any suggestions on whether I would buffer each piezo individually then mix them before the gain circuit OR have a buffer circuit plus a gain circuit for each one? I'm assuming the same 9volt will work for a number of these circuits...?
I've also come across another issue, which at first rather confused me. Both of my soundcards accept, low and high impedance signals... so that a person can plug in a balanced mic OR they can plug in an unbalanced instrument. On one of my soundcards, I switch between the two modes on the back of the unit, whereas the other is automatic. While testing my circuit, this soundcard sometimes seemed to get stuck on the wrong impedance mode... I'm working on a method to ensure the unit is always in the right mode. For example, presenting very high impedance signals (guitar passive pickups) to set it on highImpedanceMode... and very low impedance signals (passive microphone) to set it on lowImpedanceMode.
For example, would the following circuit be practical? (I've just done 2 piezo elements in this schematic for simplicity... in the real circuit I would add the third.)
Or would I have to use some kind of "summing amplifier"? Though, as of yet, I don't really know what they are, just briefly read about them in my research on opAmps.
On reflection, I would also like to add some kind of volume control for each piezo.
If you're going to do that. then use the opamp in inverting mode as a proper virtual earth mixer.
Thanks for the input Nigel. How does the following revision look? I don't think I need to reinvert the signal again in my case... but correct me if I'm wrong.
I got the circuit from:
Simple Mixer Schematics
Hi Lid,
Note for single supply operation :You will need to bias the non-inverting input of the mixer opamp to 1/2 supply voltage. and add resistors in series with the wipers before they tie in together. The series resistor (normally of equal values) on all wipers will give v(out) = -Rfeedback x (v1/Rwiper1+v2/Rwiper2+v3/Rwiper3)
Regards
Note for single supply operation :You will need to bias the non-inverting input of the mixer opamp to 1/2 supply voltage. and add resistors in series with the wipers before they tie in together. The series resistor (normally of equal values) on all wipers will give v(out) = -Rfeedback x (v1/Rwiper1+v2/Rwiper2+v3/Rwiper3)
Regards
You don't have the mixing resistors in place, so it won't work - you also have no need to add a second opamp, the original one will work fine as a mixer if wired correctly.
As shanx has pointed out, you need to provide 'bias' (actually a dummy split supply) for the opamp.
I'm in a similar boat to Lid55. I picked up a few Meas-Spec CM-01B contact mics a while back. They are the same as the basic PVDF film type he has, but these ones have an active circuit built in to give a buffered output. Datasheet: http://www.meas-spec.com/downloads/Contact_Microphone.pdf
I don't want to hijack this thread but it seemed prudent to ask here since it's so close to the situation Lid55 is in. I'd like to use these to do high quality recordings of various sources for sound design purposes. Can someone suggest a circuit to allow me to interface this with either a mic or line level input? I've never worked with PVDF elements before and am not sure where to start.
This is the Lab Amp that Meas-Spec sells for $450 that works with a variety of their sensors: http://www.meas-spec.com/downloads/Piezo_Film_Lab_Amplifier.pdf It would be nice to have all those features, but I'd just like to get these up and running with a simple circuit for now. Any help would be appreciated.
I don't want to hijack this thread but it seemed prudent to ask here since it's so close to the situation Lid55 is in. I'd like to use these to do high quality recordings of various sources for sound design purposes. Can someone suggest a circuit to allow me to interface this with either a mic or line level input? I've never worked with PVDF elements before and am not sure where to start.
This is the Lab Amp that Meas-Spec sells for $450 that works with a variety of their sensors: http://www.meas-spec.com/downloads/Piezo_Film_Lab_Amplifier.pdf It would be nice to have all those features, but I'd just like to get these up and running with a simple circuit for now. Any help would be appreciated.
Ok, here's what I've got so far, revised for a single opamp. Though I'm looking into it, I'm not entirely sure about the right component values.
I was wondering about C2, the capacitor in the buffer circuit... is it really even necessary? If it is just a bypass capacitor, for steadying the power source (which is a battery)... then isn't the 9V battery steady enough? Unless it also serves some other function in the circuit. When I disconnect it, the circuit sounds unchanged.
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