Basic Opamp Gain Stage Not Working

Started by Ripthorn, March 24, 2020, 10:00:44 PM

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Ripthorn

Alright, I feel pretty dumb about this, but I am working on a project where I have an opamp stage that isn't working. I have already checked for voltage (it's fine) and have swapped out for a brand new chip. I have good signal going into the input, but nothing on the output.  Here is the snippet of what I am doing (yes, I have stripped it down to only this on the breadboard and it is not working!). So, guru's what am I doing wrong?


Exact science is not an exact science - Nikola Tesla in The Prestige
https://scientificguitarist.wixsite.com/home

idy

feedback network goes to the inverting input....  and if AGROUND is 0v then you will need to bias the non-inverting input to mid voltage.

You are trying to do an inverting stage? Then you still bias the + input and have a resistor in series to the - input and another from output to - input. The cap goes in parallel, all feed back elements go output to - input.

There are lots of good places to see these examples...
https://sound-au.com/dwopa.htm

j_flanders

#2
Looking at the setup, most likely this is what you were after.
Gain is 1+ 27k/680r
100pF limits the gain for high frequencies
2.2uF limits the gain for low frequencies

Check any pedal schematic on how to obtain and apply the half power supply.
If there's a previous stage that already biased the signal at 7.5V and there's no DC-blocking capacitor then you can omit it.

GibsonGM

#3
Add a bias network and R to "+" input to bias at 7.5V if you're running on 15V......add an input and output cap to keep it there.

Look at a tube screamer schematic to see the network...the two 10K R's with 47u cap...
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Ripthorn

You guys were correct, thanks! I swapped the inputs and made sure I was biasing to V/2. It's working like a champ, now!
Exact science is not an exact science - Nikola Tesla in The Prestige
https://scientificguitarist.wixsite.com/home