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Preamp for piezo sensor
Preamp for piezo sensor
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Old 13th September 2019, 01:02 PM   #11
mondogenerator is offline mondogenerator  England
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Hi, the schematic I posted was just a link to a site showing an image of the circuit.

I'm fairly sure I found a simple circuit here, on Diyaudio.com...

I think it was this thread:

Piezoelectric Transducer Preamp

The TI sloa033a datasheet in post 6 is particularly useful
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Last edited by mondogenerator; 13th September 2019 at 01:07 PM.
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Old 13th September 2019, 03:40 PM   #12
voltwide is offline voltwide  Ireland
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NE5534 is not first choice for 9V applications:
-poor output level
-high current consumption
-high input bias current
-high input noise current
For a piezo tranducer the TL061 is a better choice.
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Old 14th September 2019, 07:29 AM   #13
mondogenerator is offline mondogenerator  England
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I agree.

LF351/3
TL06*, TL07, or other jFET are the best choice.

The datasheet just gives design guidance
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Old 16th September 2019, 04:07 AM   #14
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by mondogenerator View Post
I looked at simple charge amplifiers for the piezo pickup, as I was led to believe this is the best way to utilize piezo pickups.

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

Charge amplifier for piezoelectric sensors with balanced impedances at... | Download Scientific Diagram
Years ago I was using a piezo sensor as an accelerometer sensing movement of a woofer cone. I used a charge amplifier configuration, the only way to keep noise pick-up low enough while getting the extended low-frequency response I needed.

I've never used a charge-mode amp for a musical instrument piezo, simply because my guitars all came with factory piezos and onboard preamps. But I agree that charge-mode is a very good idea - it has a very low input impedance, and that solves a lot of noise and interference problems.

The circuit shown in this thread has inadequate input impedance (you want 10M for R1, not 1M), and the 5534 is absolutely not an option - use an FET-input op-amp such as the TL061 or TL071, or a more modern flavour of JFET-input op-amp.

A charge-mode circuit, by contrast, has an extremely low input impedance, but you still need an FET-input op-amp, so that the tiny signal current from the piezo goes where it's supposed to go (into the feedback network), and not into the (-) input pin of the op-amp!


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Old 16th September 2019, 08:55 PM   #15
Dinosauro is offline Dinosauro  Italy
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I made these circuit changes as you suggested:
I added 100nF to pin 4-7 power supply IC
I used TL061
I added 18 pF (I don't have 10 pF) across R5 (10K)
It seems to go much better, now I try with a good shield
Tomorrow I will do the tests on the instrument ...
Thank you very much
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