I've spent hours reading on buffers, non-inverting amplifiers and inverting amplifiers. I get the concept (though I don't understand all the formulas) and I can't make a simple voltage-follower out of a RC4558 Dual general-purpose op-amp.
Here's what I'm working with:
1V peak-to-peak sine wave @ 1kHz from a frequency generator output (50 ohms)
RC4558
Pin 1 – Output
Pin 2 – Inverting Input
Pin 3 – Non-inverting Input
Pin 4 – Ground
Pin 5 – NC
Pin 6 – NC
Pin 7 – NC
Pin 8 – +12 VDC
Signal directly connected to the Non-inverting Input.
Output feedback is connected to the Inverting Input.
The output wave is 300mV, squarish / pulsating wave.
What am I doing wrong?
Best Answer
Yes, of course you can use RC4558 op-amps for line-level audio. They have been used over the past 30 something years in lots of low end gear. They work, but the quality isn't very good: poor noise and distortion figures, poor driving ability of loads in the less than 10K range. Use something better like an LM4562 or the inexpensive and good NE5532.
It's not a great idea to leave unused devices unconnected. Connect the output to the inverting input, and convert the noninverting input to your V/2 voltage reference (or the ground in a proper dual-voltage circuit).
From your description of the circuit, you are omitting important biasing details. Since you are working with a single power supply between 0 and 12V. The center voltage is at 6V. That is to say, when there is no signal, you want the output of the op-amp to be approximately 6V. This means that the non-inverting input will have to be at 6V. The easiest way to do that is to bias that input to 6V with some resistors, and then couple the signal with a capacitor, so that the signal's AC swings are superimposed on the 6V bias.
Legend:
Note: when constructing such a device, do not route the jack sleeve connections to a ground trace on the circuit board, even though the circuit suggests that. That creates a "pin 1 problem". The jacks should be grounded directly to the power supply (or if there is a conducting chassis, to the metal chassis, which is then grounded). If there is radio-frequency interference picked up by the cable shields, this approach prevents routing it to the circuit board where it will easily find its way where it isn't supposed to.