I have built a simple inverting op amp. I am applying a 1 Vpp sinusoid at 10 Hz to a design with ~4.7x gain. The resistors I am using are 47kOhm and 10 kOhm. The op amp chip is the LT1222, and I am applying +/- 15 volts to power it. I also have 0.1uF capacitors running between the power supply and ground. The output sinusoid signal saturates around 4 Vpp, or at +/-2 Vp. From my understanding, the saturation voltage should be close to the supply voltage, and I'm not applying very much gain or a high frequency signal. What am I doing wrong?

Edit 10/3/19 12:43 PM:
Thank you for the replies so far. I have tried a few things including changing out the chip for a new one and a 741 and they both have about the same saturation voltage. I turned around the backwards capacitor and also added in a 10 uF in parallel to the others. I also replaced the short at the positive terminal with a resistor value of around 8 kOhms.

Here is a better drawing of my setup, a schematic and the actual output signal. The yellow is the amplified signal. There's some high frequency where the clipping is, but I noticed it goes away if I turn down the supply voltages to ~+/-6 V.

Wiring diagram

Schematic diagram

Photo of oscilloscope traces

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    \$\begingroup\$ Be sure to explain exactly what is connected to each of the power rails on your breadboard. There are several wires that don't do anything useful -- the black wire at row 18, the black wire from 20 to 23, the red wire in row 28, and of course, the trimpot. \$\endgroup\$ – Dave Tweed Oct 3 '19 at 13:32
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    \$\begingroup\$ One of the electrolytic caps is in backwards, a bad thing. \$\endgroup\$ – AnalogKid Oct 3 '19 at 13:33
  • \$\begingroup\$ Ah! I get it. Row 28 must be the signal input connection. \$\endgroup\$ – Dave Tweed Oct 3 '19 at 13:42
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    \$\begingroup\$ @KevinKruse I've updated the circuit to remove the wires that aren't doing anything. This used to have two op amps in series \$\endgroup\$ – Kaitlyn Oct 3 '19 at 16:56
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    \$\begingroup\$ LT1222 is not a "unity gain stable" op amp and is only stable at gains greater than 10. Try changing resistors to increase the gain. \$\endgroup\$ – John Birckhead Oct 3 '19 at 17:11

Check the opamp's output current rating. I expect it's in the 20-30 mA region.

A 50 ohm load is much lower impedance than most opamps can reasonably drive. Add about 1 kilohm in series with that 50 ohm scope input : that will give about 20:1 attenuation (at the scope) and I expect you'll get around the output voltage you were expecting.

| improve this answer | |
  • \$\begingroup\$ Thanks, this worked! Instead of adding a resistor, the scope I'm using has a setting and I changed the impedance to 1 MOhm, and it stopped the clipping \$\endgroup\$ – Kaitlyn Oct 3 '19 at 17:25

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