TL072 Stereo Headphone Amplifier

Boost a phone or laptop output to drive a pair of headphones with no clipping — two op-amps, a few resistors, and a small dual-rail supply.

Difficulty: Breadboard. Estimated build time: about 35 minutes. Estimated parts cost: about US$5.20. 12-line bill of materials. Compare supplier offers when available. A two-channel headphone amplifier built around a single TL072 dual JFET-input op-amp.

Build the dual rail

Power the TL072 from a split supply. The simplest source is two 9 V batteries wired in series: the junction between them is the new ground, the top of the upper battery is +9 V, the bottom of the lower battery is -9 V. Place a 100 nF ceramic capacitor from V+ (pin 8) to ground and another from V- (pin 4) to ground, right at the chip. Confirm with a multimeter that you read +9 V on pin 8 and -9 V on pin 4 with respect to your new ground rail.

Wire one channel as a non-inverting amplifier

Take the left audio signal in through a 1 uF film capacitor to pin 3 (the + input of op-amp A). Tie pin 3 to ground through a 100 k resistor — this gives the JFET input a DC reference. From pin 2 (the - input), put a 10 k resistor down to ground and a 47 k resistor across to pin 1 (output). Gain is 1 + Rf/Rg = 1 + 47/10 = ~5.7. The output at pin 1 goes through a 22 uF electrolytic cap (positive terminal to pin 1) to a 100 ohm series resistor and then to the left headphone wire. The headphone return ties to ground.

Mirror the channel and listen

Repeat the same network on the other half of the chip: input cap to pin 5 (+ input of op-amp B), 100 k bias to ground, 10 k from pin 6 to ground, 47 k from pin 6 to pin 7 (output), 22 uF + 100 ohm to the right headphone wire. Plug a phone or laptop into the input through a 3.5 mm jack, set the source to a quarter volume, and put the headphones on. Music should sound clean and full at any reasonable volume. If you hear a 60 Hz hum, your input cable is unshielded — twist its two conductors together or use a shielded one.