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Preamp for piezo sensor
Preamp for piezo sensor
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Old 12th September 2019, 09:10 AM   #1
Dinosauro is offline Dinosauro  Italy
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Default Preamp for piezo sensor

Hi guys, I built a preamplifier for a piezo mic for my DIY electric cello. The circuit is the following

I am not able to remove a strong oscillation which makes it unusable. Do you have any suggestions for me?
This is the piezoelectric:
RS PRO Vibration Sensor -15degC → +55degC, Dimensions 15 x 1.5 x 0.6 mm | RS Components

Thank you all, Jago
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File Type: jpg Cello.jpg (175.8 KB, 116 views)
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Old 12th September 2019, 09:16 AM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Does it oscillate without the cell connected?
Does it oscillate if not fixed to the instrument?
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Old 12th September 2019, 09:21 AM   #3
Bone is offline Bone  United Kingdom
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How have you mounted the piezo? The best place is under the bridge. However I think you would probably be better off with one of the rod pickups especialy made for instruments here 1X( Acoustic Guitar Piezo Under-Saddle Pickup S2B8) 4894462342015 | eBay . Your input impedance for your preamp (R1) is a bit low. I probably would use 4.7M to 10M.
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Old 12th September 2019, 10:12 AM   #4
gdan is offline gdan  Greece
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Preamp for piezo sensor
The common point between R2 and R3 is the virtual ground of the circuit.

Connect all the ground points there and not to the (-) point of the battery.
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Old 12th September 2019, 01:10 PM   #5
Dinosauro is offline Dinosauro  Italy
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The sensor is already installed on the instrument. The piezo is shielded and drowned in a two-component resin, in a DIY silicone mold. Output is a shielded good quality cable.
What are the signal ground I should connect between R2 and R3? The shield metal box and what else?
Thanks!
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File Type: jpg IMG_8082.JPG (319.6 KB, 94 views)
File Type: jpg IMG_7783.JPG (264.3 KB, 91 views)
File Type: jpg IMG_5958.JPG (322.4 KB, 89 views)
File Type: jpg IMG_5143.JPG (325.7 KB, 21 views)
File Type: jpg IMG_4867.JPG (317.6 KB, 22 views)
File Type: jpg Preamp_piezomod.jpg (204.9 KB, 33 views)
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Old 12th September 2019, 01:31 PM   #6
gdan is offline gdan  Greece
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Preamp for piezo sensor
Sorry my mistake. Forget my comment.
I have not seen that the power supply was only a 9V battery.
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Old 12th September 2019, 08:36 PM   #7
kevinaston1 is offline kevinaston1  United Kingdom
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Default Piezo amplifier

Attached is the service manual from an electric violin my old company did; any help for you?


Kevin
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File Type: pdf AEV44SM.pdf (534.5 KB, 26 views)
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Old 13th September 2019, 10:51 AM   #8
Mark Tillotson is offline Mark Tillotson
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Add 10pF across R5, if using the 5534 you also need 100nF ceramic cap between pins 4 and 7 (close to the 5534), always needed for proper performance of this chip.


Quote:
I probably would use 4.7M to 10M.
That would prevent the 5534 from working, and the JFET option would be required. The 5534 has a worst-case input bias current of 1.5A, which into 1M is 1.5V offset, just tolerable from 9V supply, any more and it would saturate at the rail.



A better circuit might be to use the opamp as a transimpedance stage, not a voltage amp stage, and with a JFET opamp (very low current noise).
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Old 13th September 2019, 12:06 PM   #9
mondogenerator is offline mondogenerator  England
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I nearly did something similar for my acoustic guitar, some years back.

I bought a Dean Markely piezo pickup for under the bridge, which is great as it comes with a strap button Jack socket.

I looked at simple charge amplifiers for the piezo pickup, as I was led to believe this is the best way to utilise piezo pickups.

Never got around to trying it, maybe worth a shot?

Charge amplifier for piezoelectric sensors with balanced impedances at... | Download Scientific Diagram
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Old 13th September 2019, 12:16 PM   #10
Dinosauro is offline Dinosauro  Italy
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Thanks for your advice. I will try what is suggested. If you have a better circuit ...
Thanks for the PDF of the Electric Violin, it's too complex for my needs but it's very interesting.
I will update you on the new tests.
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