Why Does My 741 Op-Amp Unity Gain Buffer Not Respond to Inverting Input Pot?

Hi - and first, thanks to all those who helped me with the last project. It was some time ago now, but the Captcha thing wouldn't let me through. It just kept going round and round... An email to eeweb got no reply.  I'm wringing this on a different pad and keeping fingers crossed.
I want to investigate the bebehaviour of an dopamine - a 741 as it's handy, so I've got a +-9v supply, pots on the input pins and a meter on the output. I've not done anything with the Offset Null pins, as I don't need super-accuracy.  I've tried to get a gain of 1 by connecting the output and the "-" input, but I think that must be what's not right.Instead of the output nicely following the sum (or difference?) of the two pot voltages, the pot on the "+ input does stuff, whilst the one on the "-" input does not much, for some reason which I hope someone will explain.Thank-you,Graham

Investigative tool for OpAmps (741)Sorry for all the typos. Hope it's still intelligible.

bebehaviour of an dopamine  LOL. That has to be a great auto-correct.Get rid of the pot on the -ve input. Unity gain will take the input on the +ve input and present it on the output. There is no summation or differencing. You can achieve that by different configurations on the +ve pin, but the -ve pin will remain used for the gain- 1 in this case.

Hi Graham-First of all, the good news- Yes- you've made an amplifier with a gain of 1, otherwise known as a voltage follower.The bad news- since the inverting input is tied directly to the output, you can't use it as in input for the pot.  The output impedance of the amplifier is very low, so it will be fighting you when you try to change the voltage on the input.   What exactly do you need to do?  A sum of two voltages (or currents) or a difference?-Rick

Hello Graham.  When you get your circuit working you'll get a dopamine hit, I'm sure :-)Your circuit would be great for testing comparators - just remove the feedback from output to -. But let's not go there for now.There are a number of good resources on the 'net for getting to grips with OpAmps:This is a great collection of reference op-amp circuits, but not much of a tutorial:
http://www.ti.com/lit/an/snla140c/snla140c.pdf
This one is more of a tutorial but not the best I have seen:https://www.electronicdesign.com/analog/how-do-operational-amplifiers-operate
Texas Instruments have a marvellous guide called "Op-amps for everyone" - it's a collection of their app notes but makes a good textbook - but they no longer seem to have it on their website. TI got taken over by National some time ago and since then a lot of resources seem to have vanished.  I have a PDF copy but can't find it after an extensive search on their site.  I can send you a copy - send me your email as follows if you'd like it- click on my name on one of my replies- you will get my profile page - under the blue box with my name are a series of links:- - click on Contact to send me a private emailI almost forgot to look on electronics-tutorials.com - they are always good.  Here's their first op amp tutorial which has links to succeeding topics at the end:https://www.electronics-tutorials.ws/opamp/opamp_1.html
And it's an Aspencore site, same as EEWeb!

Graham one other thing you could try is a circuit simulator.  For this type of thing they are pretty good.  I use NI's Multisim but there are many others.  You can configure almost any circuit configuration you want, you never have to hunt for components, you can't blow anything up.But messing around with a 741 on a breadboard is more fun  I think.... 

Yahoo tech support phone number is organised to help the customers for search issues, mailing issues and much more...