@doubledutch1962I posted previously about getting an OpAmp to work. @Audioguru again kindly posted the circuit on the right. I built that circuit and it "kind of" works but I still have a few questions.
I changed the R47K with 5K and I changed the R15K with 1K so I am expecting a gain of -5. I put my frequency generate on a constant 1V DC. My question:
- My second scope channel shows 9.2V why this value and not 5V
- If I change the voltage of my power supply by 1V - the value of the second scope channel changes by about 0.4/0.6V so if I put my power supply on 20V the Scope shows an output of 10.4. whilst at 18V it shows 9.2V. I would have expected the gain to remain the same if we stay within the operating range of the OpAmp which with 1V input, a gain of 5 should be well withing the +9 / -9 range?
I'm probably missing something very obvious but can't figure out what it is.
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I watch Dave's EEV blog a lot and also did a few courses on udemy.@doubledutch1962
A better way to learn, rather than the forum is here (Dave's EEV Blog), then what we're saying will make more sense:
I have made thousands of circuits but have not used a solderless breadboard for about 50 years because the mess of wires cause wrong connections and LOTS of noise pickup. Almost every time somebody makes a thread about a circuit that does not work properly it was because of a solderless breadboard. I properly design a circuit and its parts layout then solder its parts and a few short jumper wires on a stripboard. The parallel copper strips are easily cut and have perforated holes for the parts and jumper wires to be soldered.1) Messy wiring/noise: I never appreciated how much impact that had on what I was trying to do.
No. You changed the 0.1uF ceramic capacitor to a 100 times higher value (amount of capacitance) 10uF electrolytic. A 10uF ceramic capacitor would do the same except it would be microphonic.2) Combine (1) with the wrong type of capacitors. Changing them to Electrolytic made a huge difference
Post 17 talks about the inductance of my C2 capacitor combining that to my 5K R3 resistor, I think really messed up the Amplification ratio. So when I significantly increased the value of R4 to 500k things became a lot more obvious and I could see real (although clipped) amplification.
by Jake Hertz
by Aaron Carman
by Jake Hertz
by Aaron Carman