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I need to amplify a +1mV to +100mV input with a gain of 10.

I was thinking of using a 741 with this circuit

https://www.electronics-tutorials.ws/opamp/opamp_3.html

The specs say it's dual supply, however I don't ever remember using them with anything other than a single supply (over 20 years ago).

Will the above circuit work with a single +5v supply?

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    \$\begingroup\$ The tutorial assumes that you know how to bias any opamp to work with a single supply. Therefore the tutorial does not show power supply connections for its opamp. The 741 opamp is 55 years old with many problems and should be buried. The old LM324 quad is too noisy to amplify your very low level signal and it has awful crossover distortion. Use an audio opamp instead. \$\endgroup\$
    – Audioguru
    Mar 15, 2023 at 18:27
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    \$\begingroup\$ Reasons not to use a 741 op-amp \$\endgroup\$
    – Andy aka
    Mar 15, 2023 at 18:35
  • \$\begingroup\$ @Audioguru just seen your comment now, I placed my click 'n' collect order for the LM324 yesterday. The signal is from a load cell so basically DC changing very slowly so hopefully it will be OK \$\endgroup\$
    – KevInSol
    Mar 16, 2023 at 7:34

2 Answers 2

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Wrong tool for the job. The 741 doesn’t have enough reserve swing to work on low voltage.

The LM324 is a better old-school choice for single ended low voltage operation. Go newer and you can choose much superior op-amps that offer even wider swing on a single ended supply, such as the LMV324.

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  • \$\begingroup\$ Thanks. My local supplier has LM324N, is that the same, will it work on +5V? My output swing will be 10 to 1,000mV, if I understand. Is the LM ok for that. The LMV seems to be just SMD which is no good for me. \$\endgroup\$
    – KevInSol
    Mar 15, 2023 at 17:57
  • \$\begingroup\$ Check to see if it can swing that low (10mV). I doubt that it can, although the datasheet hints the possibility if you add a pull-down to V- (datasheet: ti.com/lit/ds/symlink/…). Otherwise You may need a CMOS op-al mp. \$\endgroup\$ Mar 15, 2023 at 18:01
  • \$\begingroup\$ I just double checked my project, while the input may be a low as 1mV, I only need to look at values higher than 5mV/50mv out. The data sheet you linked to (thanks) does not include the LM324N but I found one that did, it says Output Voltage Low Typ 5mv max 20 mV - is this the parameter I should be looking at? \$\endgroup\$
    – KevInSol
    Mar 15, 2023 at 18:24
  • \$\begingroup\$ Yes. The Output Voltage min, with Rl to V- less than or equal to 10k ohm. \$\endgroup\$ Mar 15, 2023 at 18:36
  • \$\begingroup\$ Brilliant! Thanks for your help, I'll pick up a LM324N tomorrow \$\endgroup\$
    – KevInSol
    Mar 15, 2023 at 18:40
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Looking at the datasheet we can see that the LM741 has a minimum recommended supply voltage of +/-10 V, and with +/-20 V supply rails it's output swing is +/-16 V which is pretty far from the rails, so it's not going to work very well if at all with a single 5 V supply. You'll want to use an opamp that's designed for single supply, preferably rail to rail input and output.

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  • \$\begingroup\$ Thanks for that. It was the only one that I remember using a very long time ago. \$\endgroup\$
    – KevInSol
    Mar 16, 2023 at 7:35

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