Hi All,

I am trying to put together a non inverting amp with a gain of 10.

I put it together using a 10k and 100k resistors and the opamp input voltage at 14V form a power supply.

The input signal is fed from a function gen as a sine wave @100Hz and 200mVPP. I breadboarded all of this, but my issue is that the output signal looks horrible, with no signs of it being amplified. I am sure I am doing something horribly stupid, but I could use some insight.

I have attached a couple of photos of the input/ output signals and the breadboard, any help would be appreciated

 

You need to power TL071/2/4 and TL081/2/4 from a dual bipolar supply.
It is not a single supply opamp.

 

Post the schematic.

 

Post the schematic.

Schematic: https://en.wikipedia.org/wiki/Opera...media/File:Op-Amp_Non-Inverting_Amplifier.svg

Datasheet: http://pdf.datasheetcatalog.com/datasheet/SGSThomsonMicroelectronics/mXvvyw.pdf

 

As MC noted you need a dual power supply (or you need to apply a DC offset of at least +4V to the signal.)
Alternately you could use a rail-rail type op amp.

 

Got it.

So I added another power supply channel and connected them as such :

I connected the negative lead of the first channel to the positive terminal of the second channel.

I then connected the negative of the second channel to VCC-
And the positive of the first channel to VCC+

With respect to the negative of the first channel VCC+ = 10V VCC- = -10V. But the waveform still looks about the same, I can take another picture

 

Like this?



Allen

 

If you posted a schematic of what you have, we wouldn't have to go through 20 questions.

 

Like this?

View attachment 125321

Allen

Exactly!

@crutschow I will figure out how to put together a schematic

 

I added a picture of the waveform as it is now

 

Exactly!

@crutschow I will figure out how to put together a schematic

Then you should get this....



Allen

 

Are your power supplies clean? Did you use the capacitors across the power supplies as absf showed in post #7?

If they are already there, try 100 uf.

 

I did not have the power supply capacitors .

I think things are mostly working now, but I see some bizarre behavior.

If I sweep the frequencies of the input signal from 100 Hz to 1Khz and turn on the voltage to the opamp, the output signal behaves as you would
expect. However after a few seconds I see the following yellow output signal:

Any ideas on what could be causing this?

 

Since you know how to post a photo, draw your schematic on a piece of paper. Show every component, every power supply, every signal source, every scope connection, and every component connection. Make sure each component has a unique reference designator. Take a picture. Post it.

ak

 

Done, please see attached. Let me know if I need to clarify anything specifically

 

You need one more wire from the centre of the 2 power supplies to the -ive side of the sig gen.



If you're using TL082, I think pin 4 and pin 8 are backwards. Let me check with pdf again.

Allen

 

.... Yep that was it... sigh... brutal. Thanks for your help and patience guys!

 

Hi,

Yeah, floating input

But remember one more little thing...
The gain of a non inverting amp is not R2/R1 it is R2/R1+1. Note that +1 there.
That means with a 10k resistor and 1k resistor the gain is not 10 it is 11.
Likewise, with 10k and 2k it is not 5 it is 6 because we have to add 1.