- Joined Jan 17, 2020
Absolutely not. The inverting input of an opamp that has negative feedback is a virtual ground with an extremely low input impedance. If the inverting opamp uses a 1M feedback resistor and a 10k input resistor for a gain of 100 then the input impedance is 10k which is much too low for a piezo sensor.If the signal input were to the inverting input then the bias resistors setting the positive input bias level would not be shunting the input signal. This will allow a greater load impedance to be presented to the piezo devices, and that may provide a benefit.
As said this is new to me, so glad for any suggestions and help. For now i am not to worried about sound quality as such. The Piezos are automotive sensors that will be listening to noise within automatic transmissions. The audio will be passed through FFT for analysis. I can change to OPA2134 later, but first wanted to get a basic schematic or working principal to get an output to near consumer line level.Amplified piezo "sensors" feeding headphones? What sounds are you listening to?
The MCP6002 is too noisy (hiss) for audio. You should use an audio opamp like an OPA2134 dual which has low noise but also has a minimum supply of 5V.
How much amplifier gain do you need? The first preamp had a gain of 101 and the 2nd and 3rd preamps have a gain of only 11.
Hi yes, sorry C9 was just reference is for schematic but will be just an 0402 as specified in datasheet.The automatic transmission in a car does not produce hiss sounds so I guess the MCP6002 dual opamp will be fine.
I notice that the polarity of your C9 (for HPVSS pin8) is backwards. Pin8 is a negative DC voltage that is produced.
Maybe the preamp gain should be adjustable since you do not know how loud are the sound levels. For FFT you do not want the outputs of the preamp to produce clipping.
Hee, hee. Why stereo? Which car has two transmissions?
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by Luke James
by Steve Arar