NE5532 Low-Noise Audio Preamp
The op-amp that ships in studio mixing consoles, configured as a 10× microphone preamp on a breadboard.
Difficulty: Breadboard. Estimated build time: about 35 minutes. Estimated parts cost: about US$4.20. 7-line bill of materials. Compare supplier offers when available. A non-inverting audio preamplifier with a gain of 10 (20 dB), built around the NE5532 — the dual op-amp that has been the workhorse of professional audio for forty years.
Bias the inputs to mid-supply
From the 9 V rail, place a 100 kΩ resistor to a node, and another 100 kΩ from that node to GND. The node sits at 4.5 V — that becomes the DC bias for both op-amp +inputs. Add a 10 µF cap from this node to GND to AC-ground it, killing supply noise.
Wire the first op-amp as ×10 amplifier
Pin 8 (+9 V), pin 4 (GND). Pin 3 = +input → coupling cap (1 µF) → input signal. Tie pin 3 also to the 4.5 V bias node through a 100 kΩ resistor (to set DC operating point without loading the source). Pin 2 = −input → 1 kΩ to the bias node. Feedback: pin 1 (output) → 9 kΩ → pin 2.
Output coupling and load
Pin 1 → 1 µF cap → output jack. The cap blocks the 4.5 V DC bias from reaching the next stage. Drive 10 kΩ or higher impedance loads (typical line-level input is 10 kΩ to 47 kΩ — the NE5532 is happy with anything above 600 Ω).
Test with a tone
Inject a 1 kHz, 100 mV sine into the input. Probe the output with a scope: clean 1 V sine, in phase with the input. Total harmonic distortion at this gain is well below 0.01 %. Increase amplitude until the output clips around 7 V peak-to-peak (limited by the 9 V supply rails).
Use the second op-amp
The NE5532 is a dual — pins 5, 6, 7 form a second identical amp. Wire them up the same way and you have a stereo preamp. Or chain them for ×100 gain in two stages (10 × 10) for a microphone preamp that drives line level from a dynamic mic's millivolt output.