negative supply rail to tl071 op-amp

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Joined Sep 6, 2013

using tl071 i am trying to design a audio amplifier which gets its input from microphone.the output of the op-amp tl071 is fed to the adc input of st microcontroller..
here is a attached pdf..please have a look at it.

datasheet of tl071 mentions that the supply voltage should be within +/- 15v.I am using 9v..the reason is that i get a dc offset of 4.5 v at the output of op-amp which is adequate to interface with the adc pin of microcontroller(i hope my reasoning is correct,if not please guide)..using 12v supply would be more convinient for me with respect to design of power supply but the reason i have mentioned above restricts me from using 12v supply..please guide

so my concern is if I am providing the reference voltage using voltage divider configuration at the non inverting input then do I need to provide negative supply rail of -9V to the op-amp..if so how the power supply circuit be achieved...??

one more concern is if the capacitor C30(as in pdf)is needed when the output is to get interfaced with the adc of micro??..if yes then what is the reason for it and what is the value to be decided for it.(datasheet dont mention dat).actually i saw some in some of the reference designs so i had just put it..
how the connections to be done for offset null pins??

do my design needs more things that i dint consider..please suggest..
please take out few minutes of your time and read this to help me out with my questions



Joined Jun 13, 2013
Hi Dimp,
in order to give the output a dc bias of 4.5V (as applied as the pos. input) you need a DC gain of unity. Thus, place a capacitor in series to R30.
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Joined May 11, 2009
If this stage is to be connected to a micro C33 should be removed. Also dimension R29 and R32 so that the bias point (the voltage at pin 3 U10 with no input signal) is the midpoint in the ADC conversion range


Joined Jan 20, 2014
Normal DC offset for the ADC would be 2,5V, wouldn't it?
Check the datasheet for Your ADC and select Your supplyvoltage to be 2 times that.
Also I would have made an inverting ampstage here, where the non-inverting input just could be earthed, The R30 directly to the input capasitor and remove the output capasitor.

OR, just keep the output capasitor and have the ADC to determine it self for the DC-offset voltage. (Most will do)