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I have tried to make signal amplifier just to gain some op-amps knowledge, but unfortunately it doesn't work. It simply doesn't reach desired voltage (set by resistors). I have used my old cellphone headphone audio output as an input for op-amp. The OPA454 was powered by +/-15 VDC from two 5V to 15V step-up conventers. The wiring looks like: wiring

And SSs from scope with different gain. Please see peak-to-peak voltage below graphs: screen shot 1/3 screen shot 2/3 screen shot 3/3

For some reason it can not exceed 10V peak-to-peak even through it should (based on my poor knowledge). Why it does so? One more thing is that I use adaptor so that it is possible for me to plug OPA454 to breadboard, but I am pretty sure it is designed / soldered correctly. I have tried swapping opamp to another one but it does't change anything. What could be potential issue?

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  • \$\begingroup\$ You're clipping. Are you sure you're using +/- 15V? \$\endgroup\$
    – Sean M
    Commented Nov 12, 2018 at 17:10
  • \$\begingroup\$ @SeanM I am 100% sure. Just measured V+ to V- right on OPA454 pins and it is 30VDC. \$\endgroup\$
    – 3Qax
    Commented Nov 12, 2018 at 17:15
  • \$\begingroup\$ Are you driving a load? Could you, just for the sake of being complete, check that the scaling on your O-scope and probes is correct? From the datasheet, if you're not driving less than a few k-ohms you should get to about 1V away from the rails. So it's not rail-rail, but it's pretty close. \$\endgroup\$
    – TimWescott
    Commented Nov 12, 2018 at 17:29
  • \$\begingroup\$ Try swapping the probes over. \$\endgroup\$
    – Andy aka
    Commented Nov 12, 2018 at 17:31

1 Answer 1

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Your Hantek 6022BE scope is clipping at ±5V.

The manual states:

Max. Input +/- 5V(Without external attenuation)

You need a 10× probe if you want to measure voltages outside this range.

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  • \$\begingroup\$ Well that was my issue. Setting switch on my current probe to 10x and then changing this value in software helped. The thing is that I was mislead by text on the scope - “max +/-35V”. Will add appropriate tags in a moment so that other people could find this. Thanks from the bottom of my heart - I would never think of that. Note to self: RTFM. \$\endgroup\$
    – 3Qax
    Commented Nov 12, 2018 at 17:59

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