# [explanation needed] - acoustic op amp

Discussion in 'The Projects Forum' started by Rafał Kotrys, May 24, 2016.

1. ### Rafał Kotrys Thread Starter New Member

Apr 22, 2016
12
0
Hi Folks,

I was looking for an op amp to a project of time grapher. I found a circuit which could be adjusted to my project, but I need some explanations as I'm rookie to electronic topics and probably it's my first and last project done. Could I ask more experience Guys to help me with it?

Below is the cirucit of two step op amp.
J2 is supply voltage from stabilized power supply +5V.
J1 is input signal. Low voltage microphone signal (level 0,5mV)
J3 is output signal.

Questions:
Capacitors C2, C3, C4, C5 are used to prevent power supply from sudden changes of voltage, am I right? Why we use 4 and 2 with 100nF and next two 220uF. Is there any method to determine those values? I was thinking about input signal from microphone. If level of this signal is about 0,1mV and voltage changes should be respectively 100-1000 times lower to avoid situation that low changes of power supply signal when are added to the microphone signal can make in total big changes to output signal. Am I right?

Resistors R2 and R1 what are the reason they are placed in the placed in which they are placed.

Branch 14 with Resistor R4 and R8. Is it used to prevent ciruit from sudden changes of current? Are they used to stabilize the current flow in the circuit?
What is the purpose of R7 and C6 capacitor? Why R4 is made as a feedback to first op amp?

Capacitor C1 and C7. I read somewhere that capacitors at output are used to cut off the constant voltage from signal. How to determine proper capacitor value? Will my signal be symetrical to 0 V instead of some constant value after signal pass C7? I wanted to put this signal next on comparator and I'm wondering because description of comparator tells that device should be used only for positive voltage.

Why C1 is placed on the input of 1st op amp?