Basic question

[michael_krell]

I am trying to construct a simple non inverting amplifier circuit with a jrc4558 and a 9V battery. Im using 2 10K resistors. I know this will only give unity gain but im not even getting that. My question is does the output impedance of my scope have anything to do with it?

also when i tried to use a 741 I got unity gain but the lower half of the sine wave was chopped of. Im confused

[R.G.]

You have a bias problem. Older opamps, especially the 741, will not push their outputs closer than aobut 2V to the power supply limits. You must provide a bias voltage approximately in the middle of the power supply limits to get it to work.

In this case, take two more 10K resistors, tie them between +9 and ground and tie the + input to that. Now the 10K to the - input and 10K feedback resistors will give you an inverting gain of 1.

However, you must also make sure that whatever you hook to the circuit does not upset these DC conditions, so you must block the incoming signal's DC level (even if it's 0V) with a capacitor big enough to not cut any bass response you want. For 10K, 10uF should work. You must also provide a DC-blocking cap at the output. Further those caps have to be oriented with their + sides correctly on the most positive side, in this case toward the opamp.

You could also use another 9V battery, + side tied to the - side of the first one, and have +/-9V. The +9V goes to the + power pin on the opamp, the -9V goes to the - power pin, and the middle of the two batteries ties to the + input. Now the DC blocking capacitors are not needed if you use the junction of the two batteries as signal ground.

You need to read about bipolar power supplies for opamps and single supply operation of opamps. I'll see if I can find a reference. They're pretty thick on the net.