Inverting Amplifier Circuit HELP!

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Studioalethea
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Inverting Amplifier Circuit HELP!

Post by Studioalethea » Tue Feb 11, 2020 1:31 pm

I have been struggling with something quite fundamental: the inverting amplifier. I know there is clearly something fundamental that I am just not understanding about the basics.

I have been successful in creating non-inverting buffer circuits but whenever I try to place the feedback resistor in the NI configuration I just lose sound entirely. This happens across all the chips I use, so its clearly something that I don’t understand about the voltage divider at the front end of the circuit.

Did anyone have a similar struggle when they started out? Did you have an a-ha moment that you could share? Also, does anyone have a breadboarded 2x gain inverting buffer circuit on a breadboard to show me my error?

I am mostly just trying to bump up my 2V peak to peak triangle up to something closer to my 5V square on both my 566 and 40106 VCO circuits. I am using 10 ohm on the input and was trying 22 ohm for the feedback resistor.

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Graham Hinton
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Re: Inverting Amplifier Circuit HELP!

Post by Graham Hinton » Tue Feb 11, 2020 1:37 pm

Studioalethea wrote:
Tue Feb 11, 2020 1:31 pm
I am mostly just trying to bump up my 2V peak to peak triangle up to something closer to my 5V square on both my 566 and 40106 VCO circuits. I am using 10 ohm on the input and was trying 22 ohm for the feedback resistor.
There's your problem, try using 10k ohms and 22k ohms.
10 ohms would imply a current of 200mA and neither the source nor the op amp are going to provide that.

Studioalethea
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Re: Inverting Amplifier Circuit HELP!

Post by Studioalethea » Tue Feb 11, 2020 7:40 pm

Worked like a charm! I actually realized that I could power the 566 with both rails (since the op amp already requires it), so I have a 10V p2p now and what originally needed a 24k fb resistor to match the square at 5V p2p now only needed a 20k.

Is 10k pretty standard for the input side of a TL07x? Any thoughts on the AC decoupling cap on the front end with it?

Thanks for the help!
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jorg
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Re: Inverting Amplifier Circuit HELP!

Post by jorg » Wed Feb 12, 2020 5:16 pm

Of course the exact values are very dependent on what the circuit is supposed to do and what other circuits it interfaces with. But in general, in audio design with op amps, resistors are in the tens of kohms to a couple of hundred kohms. There are exceptions, but tens of ohms would be uncommon, and the main rule of thumb to apply is Ohm's Law.

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