TL072 amplifier on +-12 V

// A TL072 inverting amplifier on a split supply, +12 V and -12 V.
//
// The TL072 is the LM358's pinout with faster, JFET-input op-amps inside,
// and it is made for a split supply: pin 8 (VCC+) on +12 V, pin 4 (VCC-) on
// -12 V, and the signal measured from the ground between them. That is the
// supply a textbook draws, and it is what lets the output go below ground.
//
// Amplifier 1 is an inverting amplifier with 10 k in and 47 k of feedback,
// 1IN+ (pin 3) on ground. Its gain is
//
//   -Rf / Rin  =  -47 k / 10 k  =  -4.7
//
// The generator makes a 1 kHz sine of 1 V peak about 0 V. The scope shows it
// on channel 1 and the output on channel 2: 4.7 V peak, upside down, swinging
// from -4.7 V to +4.7 V about ground.
//
// Things to try:
//   - Turn the amplitude up to 3 V. The output wants 14.1 V peak and stops at
//     about 10.5 V either way: a TL072 stays 1.5 V inside each rail.
//   - Wire VCC- (pin 4) to ground instead. The output can no longer go below
//     1.5 V, and half the wave is gone. That is why this chip is not for a
//     single 5 V supply.