Op-Amp design 1

[pcough]

I need help with a design of an op-amp...

Constant input of 3.2v peak-to-peak.

I am using a biased non-inv buffer amplifier, then want to control the gain of the next stage between about 300mV and 16V peak-to-peak. I have a single-rail +28v dc supply (biasing the amps to a virtual ground of 14v).

I need to use a 741 or similar op-amp, but all other components should be available.

Currently, I have fixed the gain at 5 and tried to use a potentiometer (4k7 lin, with 100R fixed to earth) at the input of the amplifier to sweep the input between ~67mV and 3.2V. However, my output is simply not good and shows clipping on the -ve side of a 1kHz tone input.

I'm desperate here....

TIA

Pete

 

[Lewish]

OK, first off, you need to understand that an Opamp powered from a single +28 volt supply cannot swing an input signal anywhere near to 0 volts. The closest you can get without clipping is about 2 volts from either rail, so 2 volts and 26 volts is the maximum peaks of your output signal.

Go back and rethink your approach, or post a more complete description of your circuit for more help here.

 

[Chuckles159]

You need to use an AC coupled circuit with the op-amp biased at 1/2 the supply voltage. I suggest Jung's Op-Amp cookbook as a reference if you're going to dabble with op-amp circuits.