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TOPIC: Optimum swing at input to first opamp

Optimum swing at input to first opamp 2 months 1 day ago #611

  • brownt
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What would the optimum AC voltage be at the input to the first opamp? I guess the optimum output is 5vpp, is that correct?
Last Edit: 2 months 1 day ago by brownt. Reason: typo's and additional info
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Optimum swing at input to first opamp 1 month 4 weeks ago #617

  • Ray
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Having a look to the TL972 datasheet you can see that the input voltage range (page four) is:
VCC– – 0.3 and VCC++ 0.3
so if you are powering at 5V, the optimum input voltage is 5V - (2*0.3) = 4.4Vpp
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Optimum swing at input to first opamp 1 month 2 weeks ago #648

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I see thanks. I am only geting 2.5volts at the output of the opamp before clipping starts to occur. clipping ocurs at the top first. The bottom of the signal increases about another volt before it too clips. any ideas?
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Optimum swing at input to first opamp 1 month 2 weeks ago #653

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you are using the TL972 op amp, arent you?
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Optimum swing at input to first opamp 1 month 2 weeks ago #654

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no, LM358. I suppose that's the reason.
I tried a MCP 602 and that gets 4 or so, volts swing. Can you tell me what the difference is. I mean what should I be looking for on the datasheet? thanks
Last Edit: 1 month 2 weeks ago by brownt. Reason: adding comments
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Optimum swing at input to first opamp 1 month 2 weeks ago #655

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I have checked the LM358 datasheet:
www.ti.com/lit/ds/symlink/lm358.pdf
And the input voltage levels (Vcir) should be between VCC -2V, so powering at 5V, the input voltage swing goes from 0 to 3V, so the clipping you see could be normal, we choose the TL972 because it is rail-to-rail and admits a wider range of input voltages.
I would suggest you to adjust the VR1 input trimmer so the guitar input levels stays between 0 and 3V.

Every op amp datasheet sates the input voltage swing in a different way, the TL972 has a graph on page 4, the LM358 call it ""Common-mode
input voltage range", etc
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Optimum swing at input to first opamp 1 month 1 week ago #660

  • goku546578
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brownt wrote:
no, LM358. I suppose that's the reason.
I tried a MCP 602 and that gets 4 or so, volts swing. Can you tell me what the difference is. I mean what should I be looking for on the datasheet? thanks

Hello brownt, did it work with a LM358? if so, could you please tell me if i needed some special arrangement?

thanks a lot!
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Optimum swing at input to first opamp 1 month 1 week ago #662

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I don't know a lot about these things, but it seems that the output swing was limited to about 2.5volts with the LM358, and the gain seemed low. I changed R4 from 4K7 to 1K to increase the gain. But in the end I used a MCP602 and the swing changed to about 4 volt peak to peak.
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