Purple is input from AD9850 and Green is output measured over the load resistor and pretty much same signal if I measure the output directly with no load resistor)I am trying to amplify a simple 120mVPP sine wave (4K Hz) to a 5VPP signal being made by an AD9850 being controlled by a raspberry pi. We started off using a 741 but realized after asking you guys that 741's are garbage and attributed the output being clipped at ~2.8VPP to it being a 741 (We had the supply at +-15V). We then moved on to try using some more recommended OPAMPS such as a TL072CP and a OPA2227P and ran into the same exact "clipping" issue all being run at their recommended max voltage supply +-15 (We were able to get ~3VPP with these but no where near what we expect to see out of the OPAMP). At this point I am assuming it may not even be a clipping issue (despite it looking like clipping). I was wondering if anyone had any insight into what may be causing what looks like clipping at 12 volts lower than the rail on multiple different opamps?

We want to run the amplifier off of 5V or 10V preferably which should be fine if the OPAMP is rail to rail but if this is not possible with an OPAMP realistically then we read that using an instrumentation amplifier may be a better path too if anyone has any input on that?


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. \$\endgroup\$ – Dave Tweed Jan 3 '18 at 16:22
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    \$\begingroup\$ I'm thinking you are not seeing what you think you are seeing and the signal shown is actually x10. or at least the scope THINKS you are using a x10 probe. Use the same probe to measure the rail voltages. What do you get? \$\endgroup\$ – Trevor_G Jan 3 '18 at 16:57
  • \$\begingroup\$ @Trevor the probe is 10x \$\endgroup\$ – Paul Jan 3 '18 at 17:17
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    \$\begingroup\$ @Trevor we had the probe in the 1x slot apparently thanks for the help!! \$\endgroup\$ – Paul Jan 3 '18 at 18:41
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    \$\begingroup\$ @Paul ;) we have all done it, usually more than once. Hence I always double check the probe with the rail before relying on what it says on the screen. Have fun. \$\endgroup\$ – Trevor_G Jan 3 '18 at 18:43

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