here's the preamplifier i want to use, maybe something wrong in the connection!
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No.I tested the mic by detecting the heart sound and I connected it directly to the oscilloscope, the maximum output voltage was 800mV!
For your information and since you want to learn.You do not want to match the input impedance of the amplifier to the impedance of the microphone. You want the input impedance of the amplifier to be much higher than the impedance of the mic so the level from the mic is not loaded down.
Then I was young we did not have any internet. But I learned a lot by browsing through data books and study circuit examples. And so can you. If you take a circuit given to you and work with it until you understand it you have learned something. And you can also learn a lot by simulating your circuit.i just didn't use yours because i wanted to learn from my mistakes instead of just following a ready circuit!
i tested your circuit today but i only changed R1 resistior value to 2.2K as stated in my mic datasheet! (i don't know if this gonna affect the values of other components !?)It is too bad that you did not make my mic preamp circuit that works.
Zap that chicken at once - he talks too much sense.Then I was young we did not have any internet. But I learned a lot by browsing through data books and study circuit examples. And so can you. If you take a circuit given to you and work with it until you understand it you have learned something. And you can also learn a lot by simulating your circuit.
Then you ask questions in this forum it is also important that you post the circuit you are using in the first posting. That will ensure you that we do not go around blindfolded trying to help you. And you get your answer much faster.
If am correct, he just had extra 1k resistors laying around and didn't want then to go to waste. Odd that it didn't work without it.one more thing, what's the role of 1K resistor in your circuit ? i tried to remove it but it didn't work without it !!
if it's as you said, then how about the feedback resistor and R4 !? shouldn't i set the gain through them? im confused here[ed]
Sorry, needed a comic relief moment.
The ratio between the 1k and 100k gives you the gain for the amp. In this case the gain is set to 100 (100k / 1k)
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The gain is set by VR1 and R4. To simplify analysis think about C2 as a device that block DC 100% and have Zero resistance for AC. Let us also say the that no current will flow into the OPAMP input. Then for DC this circuit will have gain equal to 1, and for AC the gain will be (1+VR1/R4)if it's as you said, then how about the feedback resistor and R4 !? shouldn't i set the gain through them? im confused here
The value of R1 is affected by the supply voltage. 2.2k might work well if the supply is only 3V.i tested your circuit today but i only changed R1 resistior value to 2.2K as stated in my mic datasheet!
I don't know what you mean "but it didn't bias it". My circuit uses R2 and R3resistors to bias the input of the opamp to half the supply voltage.The circuit has amplified the signal well but it didn't bias it, although it amplified the both side of the signal!
If the circuit is built correctly then the output pin of the opamp will measure at half the supply voltage on a meter and on an oscilloscope.Will i get a value of half of the supply voltage if i connected the output directly to the multimeter? Or is it observed on the oscilloscope that the signal is biased up?
It makes a filter with the 47uF capacitor so that fluctuations in the supply voltage do not feed into the input of the opamp. The bias voltage for the opamp and the bias current for the microphone pass through the 1k resistor so the circuit will not work without it.What's the role of 1K resistor in your circuit?