Hi everyone,


I'm very new to electronics world and would like to build a basic non-inverting amplifier using the LM7171 BIN op-amp. My goal is to amplify a 1V DC input, and I'm using a simple feedback configuration: a fixed 1kΩ resistor from input to ground, and a 10kΩ potentiometer from output to the inverting input.

The problems are:

1. Output Doesn't Vary with Potentiometer
When I turn the potentiometer, the output doesn’t change — it stays at around 1V, matching the input. Only when I rotate the pot all the way to max (10kΩ) do I get an output of ~5V, which I assume is due to gain clipping (my supply is ±5V).
But I expected a gradual increase in gain/output as I adjusted the pot. For example, halfway (~5kΩ) should give a gain of 6 and ~6V output (before clipping), but it still reads only 1V.



2. Op-Amp Overheats at Higher Supply Voltages
When I increase the supply from ±5V to ±10V or ±15V, the op-amp gets very hot, even if there's no signal input.
I verified the power pins are correctly connected, and my soldering is clean — no bridges or shorts.
The datasheet says the LM7171 supports up to ±15V, so I’m not sure why this is happening.

I tried adding decouplig caps of 0.1 uF and 10 uF from +V to GND and -V to GND but it deosnt help.

Please could anyone help me please? Attached you can find the circuit on a veroboard and also the schematic. Thanks!

Please ignore everything starting from the grey wire, they are a previous circuit that I already get rid of!

 

We need more information before we can offer any suggestions. Can you give us a real electronic circuit diagram using international symbols, with labels on the power source and pin numbers on the IC please. A hand drawn sketch will probably be enough.

 

We need more information before we can offer any suggestions. Can you give us a real electronic circuit diagram using international symbols, with labels on the power source and pin numbers on the IC please. A hand drawn sketch will probably be enough.

Hi Keith,

This is what it looks like. R3 is the variable resistor, and R2 is the fixed 1k resistor. Input is 1V DC. And the op amp was supplied with +-5 V as specified by the datasheet

 

I will assume that the 1 volt source not connected to ground is a drawing mistake but in your circuit it is actually connected.
Am I assuming correctly?
Edit ; I will also assume that your negative supply, as shown is also a drawing error.

 

I will assume that the 1 volt source not connected to ground is a drawing mistake but in your circuit it is actually connected.
Am I assuming correctly?

Hey, yes, this is how i connect the power supply

Blue -> +
orange -> Ground
Black -> negative and 1V

I used keysight triple power supply

 

Has you have your mounted circuit the potentiometer is shorting the ampop output to 5v/0v at the extremes.
You only need to connect 2 terminals of the potentiometer to match your circuit diagram.

 

If that's Veroboard, have you cut the traces under the IC?

 

If that's Veroboard, have you cut the traces under the IC?

Yes

 

This is what the circuit from the second image of the first post looks to me. Makes sense the output doesnt vary if it is a buffer.

 

View attachment 350389

This is what the circuit from the second image of the first post looks to me. Makes sense the output doesnt vary if it is a buffer.

That make sense, i screwed up with the wiring and accidentally wired it like a voltage divider! Will try again tomorrow, thanks so much!

Do you think the heating of the op amp is due to this or could be other reason?

 

When the pot is at one of its extremes the output will be driving through a low value load to +ve or ground - that will cause it to overheat for sure.

 

@flyingphoenix A few points to note:
1. Add 0.1uF decoupling capacitors (ceramic MLCC preferrably, ceramic disc would also do) at both positive and negative power supply pins.
2. You are trying to amplify a 1V from 2V to 11V. Op-Amps are limited by their input range and output range. Since V_EE = -5V and V_CC = 5V, the output voltage can only swing between this range (i.e.) -5V to 5V and not beyond them. Increase the supply voltage magnitudes for the circuit to work properly.

Your heating issue might be caused due to noise (since decoupling capacitors are not present) or due to unconnected pins (datasheets usually suggest unconnected input pins to be grounded or pulled to supply voltage).



Please refer to https://www.ti.com/lit/an/sboa092b/sboa092b.pdf for more guidance on OP-AMP based circuit design.