Opamp TL071 supply voltage clarification

[vikash23]

Hi,

I need to use a supply voltage of 12V to 24V to opamp. TL071 maxiumum supply voltage is +/- 18V. I wont be using the negative voltage , in that case will this op-amp can able to cope up with 24V input ?

Will I be able to use NE5534 ? but the maximum input voltage is +/- 22V?

 

[barry]

The opamp has no way of knowing whether you've got +/- 18 or 0 and 36. You'll be fine with 24V. If you read the note on the data sheet, that should help:

1. All voltage values, except differential voltages, are with respect to the midpoint between VCC+ and VCC−.

 

[vikash23]

Hi Barry,

Could you please let me know how to set the gain of the op-amp.

I assume i need to use a potentiometer at the Vo of the opamp. gain=1+R2/R1.

Can I please know for 5V supply voltage for opamp TL071 if I use R2=1Mohm and R1=10K will I be able to get 101dB gain ?

Thanks.

 

[barry]

Why do you need a pot? You've just said that gain is 1+R2/R1 (assuming a non-inverting configuration). If you need adjustable gain you could replace R1 or R2 with a pot.

You've got the formula right in front of you, why are you asking me? (The answer is: you've got 40dB of gain)

Asking for 101 dB of gain out of a single opamp might be asking too much; you may want to use two stages.

 

[godfreyl]

if I use R2=1Mohm and R1=10K will I be able to get 101dB gain ?

No. Gain = Vout/Vin = 101 = 40dB
Because 20*log(101) = 40

btw, A single 5V supply is probably too low. +-5V is OK.

 

[adi0803199]

5V supply voltage for opamp TL071 if I use R2=1Mohm and R1=10K will I be able to get 101dB gain ?

When you say that you use the value of feedback resistance as 1MΩ,you need to understand that the op-amp most probably won't work as theoretically the input impedance between the two inputs should be infinity,but in reality it will be in the order of MΩ.So check the data sheet and I would suggest you using R1=1kΩ and R2=100kΩ.The gain that you get is 40 dB.

 

[godfreyl]

theoretically the input impedance between the two inputs should be infinity,but in reality it will be in the order of MΩ.

The TL071 is a JFET-input opamp. It's input resistance is typically 1TΩ i.e. 1000000MΩ. So that won't be a problem.

 

[Audioguru]

Texas Instruments designed and makes the TL071 opamp. They say its minimum supply is 7V.
I have made many preamp circuits with it powered from a 9V battery and it still works well when its voltage drops to 6V and the output is 1Vp-p.

A voltage gain of 100 times is +40dB.

 

[vikash23]

Hi,

Thanks all for your reply.

My amplifier is working but the output seams to be very noisy when I speak through the mic.

Could you please let me know how to minimize the output noise.

Below is my circuit diagram where I remove the filter and used a 0ohm link since the filter dint make any difference.

Is the noise is because of the variable gain (potentiometer) on the output ? or is it amplifying the input noise ?

 

[Audioguru]

You did not describe the noise. Hiss? Hum?

Your schematic drawing software is a nightmare. Why isn't the negative feedback connected directly to pin 2?
Your schematic does not show the supply voltage so maybe it is too low. 7V is the minimum for a TL071 opamp.

What kind of mic? I hope it is an electret type. Your schematic should say so.
The value of R5 is too low (1k) and is shorting the signal from the mic. Use 4.7k.

The values of all the parts in both filters are very low impedance so the input filter is shorting the signal from the mic and the filter at the output of the opamp is causing the opamp to oscillate at a high frequency which makes hiss noise. Remove both filters then the mic level will be higher and the opamp will not oscillate.

You need maximum gain to be 46dB but 40dB will also work. 100dB is crazy because the output rumble and hiss noise will be high and audio frequencies above 32Hz will be reduced.
Please learn about dB's. A gain of 100 times is +40dB. A gain of 1000 times is +60dB. A gain of 10,000 is 80dB. A gain of 100,000 is 100dB.

If a breadboard is used instead of a printed circuit board or a compact stripboard then the opamp will probably oscillate.