I have just completed the first stage of my project and have a question regarding the LM3900 chip, on the input i have such a small sinewave it is barely visible with the scope, meanwhile i have a thumping great sinewave on the output pin, it's beautiful!!!

So what is the gain of the LM3900? it must be huge?

Neil.

 

In this thread:
http://forum.allaboutcircuits.com/showthread.php?t=62843
you said you would attach a schematic next time.

I don't see it?

The open-loop gain (no feedback) is 70 dB.
Every 3 dB is a half-power point.

 

That very old LM3900 amplifier is not an opamp, it is different.
I am surprised that it is still being manufactured.
Why don't you modify the circuit a little so an ordinary opamp can be used?

 

I am surprised that it is still being manufactured.

I am pretty certain that most of these ICs are no longer actually in production. They couldn't be, there is next to zero commercial demand.

I mean, the preparation work / tool cost to do a run of chips is probably only a few million dollars

But 0.0000001 cents a piece after that initial fee.