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Op amp not working out as planned

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netdudeuk:
Guys

Thanks for all the replies.

My circuit may not be there yet but I've learned plenty in the meantime.

Looking at the schematic though, I'm pretty sure that the Great Scott video used a 5v supply with that op amp.

I have some MCP602s so I'll try one of those.

Mechatrommer:

--- Quote from: netdudeuk on March 05, 2018, 05:22:57 pm ---Looking at the schematic though, I'm pretty sure that the Great Scott video used a 5v supply with that op amp.
I have some MCP602s so I'll try one of those.

--- End quote ---
no opamp in this world can produce 6V from 5V rail, let alone -6V in inverting amp as your setup that i missed to see.

netdudeuk:

--- Quote from: Mechatrommer on March 05, 2018, 05:36:49 pm ---
--- Quote from: netdudeuk on March 05, 2018, 05:22:57 pm ---Looking at the schematic though, I'm pretty sure that the Great Scott video used a 5v supply with that op amp.
I have some MCP602s so I'll try one of those.

--- End quote ---
no opamp in this world can produce 6V from 5V rail, let alone -6V in inverting amp as your setup that i missed to see.

--- End quote ---

If I get your meaning, I was just saying that he seems to have used a single 5v supply rail (which, according to Hero999,  isn't supported), not that he was getting 6V out.

Andy Watson:

--- Quote from: netdudeuk on March 05, 2018, 05:22:57 pm ---Looking at the schematic though, I'm pretty sure that the Great Scott video used a 5v supply with that op amp.

--- End quote ---
Those op-amps will be a bit lethargic at 5V - they are not designed for such low supply voltages. Your signal amplitude will be limited - fortunately you do not need much amplitude for a mic signal, but you do need to bias the op-amp into its working range.


--- Quote ---I have some MCP602s so I'll try one of those.

--- End quote ---
I think you are going to half-disappointed ;) Consider applying -100mV to the input and calculate the voltage at the output. Now repeat the exercise with +100mV at the input - it should be obvious why it's not going to work. 

netdudeuk:
Hi

I've replaced the NJM5532 with a MCP602 (http://ww1.microchip.com/downloads/en/DeviceDoc/21314g.pdf) running at 5V with the non-inverting input biased to 2.5V with two 10k resistors.

This is a single rail (2.7V to 6V) device with Rail-to-Rail output.

Things seem to look better on the scope.  No clipping.

I have a 4.7k resistor on the input and a 5.1k resistor in the feedback loop.  I was expecting the gain to be 5.1/4.7 = 1.085106382978723

I'm assuming that the actual gain is ( Vpp (Output) /2 ) / (Vpp (Input) /2 )  i.e. 360/280 = 1.285714285714286

So, theory and practise don't match up.  I'm assuming that's it is probably my theory that's not right  :)

What's the situation here ?

Thanks

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