Can i use a comparator as an Opamp ??

[audioguru]

I appreciate your help audioguru .

I gues you use use them a lot for your audio amplification ?

I used a lousy old 741 opamp only one time:
1) It produced a lot of hiss because it was not designed for audio.
2) It cut frequencies above only 9kHz (we can hear to 20kHz) because it was not designed for audio.
3) It produced distortion because it was not designed for audio.

Then I used MANY TL071 single, TL072 dual and TL074 quad audio opamps because they have low noise, have a bandwidth to 100kHz and have very low distortion at 0.003%.

 

[BGAmodz]

Ok i see .

While you have experiance with opamps , would you please explain to me how it works internally ??

Lets take for example this design : opamp in differencial mode

In this setup the output 'vo' = 3(v2-v1 )

How can i prove this equation depending on this schematic ?? r1 is 2k

 

[audioguru]

<Text> Your <Text> schematic drawing software <Text> is <Text> a <Text> nightmare <Text> <Text>.
I used simple Ohm's Law to calculate things in your differential opamp circuit.

 

[BGAmodz]

Ok i get the first part concerning the + input , but since we got 7 volts on V1 , we have R1 and R4 in series , we can get the current using this way : 7v/(2k+6k) =0.85 mA ?? no , and then get the input voltage on R4 = 6k * 0.85 mA = 5.25 v ???

 

[audioguru]

Ok i get the first part concerning the + input , but since we got 7 volts on V1 , we have R1 and R4 in series , we can get the current using this way : 7v/(2k+6k) =0.85 mA ??

No, because you do not know the output voltage yet and it is not 0V anyway. The current in R2 and in R4 IS NOT 0.85mA. There is 0.5V across R2 so its current is 0.5V/2k ohms= 0.25mA. The same current is in R4 so it has a voltage of 0.25mA x 6k ohms= 1.5V across it. Pin 2 is +7.5V so the output is 1.5V + 7.5V= 9V.

no , and then get the input voltage on R4 = 6k * 0.85 mA = 5.25 v ???

Completely WRONG.