# In testing this op-amp, I always get same amplification. Did I break it?

I bought these TL072 (maybe TL072CD) IC amps, for a circuit I was trying to build, but the circuit wasn't working at all so I tried to troubleshoot the amp.

I built a voltage divider ~1/1000 (on the left of the pictures) and different amplifier circuits (inverting and non inverting with an amplification of roughly 100) for both op amps in the IC, but I always get the same 8.7V reading (supply is 9V).

I also tried switching the resistors around to create ~1/100 amplification, but as soon as I connect the power source, the output voltage is 8.7V. Did I break the amp?

This is the rough overview for the amps internals:

Here's some of the circuits I have tried:

Inverting circuit on the second internal opamp:

Non Inverting circuit on the second internal opamp:

Inverting circuit on the first internal opamp:

(Hard to see but the bevel is at the bottom side of the IC)

All three give the same output voltage (between opamp output and minus of battery) of 8.7V.

EDIT: I must have used the wrong resistor R3 in the photos (10K instead of 1K) so gain must have been more ~10 Here is a circuit diagram:

simulate this circuit – Schematic created using CircuitLab

I think by drawing it, i get it now (supply voltage was always just a number for me up to this point i never worked with it). I think that, if i change the voltage divider to this it should probably work (pls feel free correct me on this):

simulate this circuit

FINAL EDIT: Thanks again for all the suggestions, by creating a virtual ground the amp behaves now in a range where i expect it to behave. Your advice was valuable and now I know what to change on my main project :)

• Even if the opamp were ideal, your inverting test circuits could never function since both your input voltage and opamp negative supply are the same point. It can't give you a negative output without a split supply. Aug 10, 2023 at 13:43
• Can you provide a real circuit diagram, as well as every resistor value you've used?? I suspect your issue is as already described in the answer, but you may have more problems, too. Aug 10, 2023 at 15:27
• nice spider ... Aug 10, 2023 at 17:54
• Now that you've drawn the circuit diagram using CircuitLab built into this site, you can measure the DC operating point of the thing, and see if it matches the specifications. To evaluate the effect of offset, add a DC voltage source set for 5mV in series with either the (+) or the (-) input. Flip that source around (select with mouse, press X or Y as needed) to see what happens when the offset swings between its extreme values. "This should be ...": the circuit you got is a live DC simulation. You can actually read what it is :) Aug 10, 2023 at 20:41
• What do you want the circuit to do? Be specific. You built something. Why did you build it? What do you want it to do? Otherwise I have no idea what you're trying to achieve. Please perhaps draw (on paper, then take a photo) a DC transfer function you'd like to get, i.e. the input-to-output voltage relationship, with input voltage on X axis, output on Y axis. The slope of any non-horizontal line segments in the response determines the gain in that region. I built a voltage divider ~1/1000 Cool. Why? Aug 10, 2023 at 20:44