This 3 channel 15 LED spectrum analyzer is the perfect addition to any audio amp project. It produces fantastic displays on three LED bars that can be individually adjusted for any particular frequency range. The circuit will take line level output from most any audio source, and operates on 12V DC. This means that it can even be run in a car.
| R1 | 1 | 100K 1/4W Resistor | |
| R2 | 1 | 820K 1/4W Resistor | |
| R3, R14, R16, R18 | 4 | 2.2 Meg 1/4W Resistor | |
| R4, R5, R6 | 3 | 22K Pot | |
| R7, R8, R9, R25, R27, R29 | 6 | 10K 1/4W Resistor | |
| R10, R11, R12 | 3 | 680 Ohm 1/4W Resistor | |
| R13. R15, R17 | 3 | 580K 1/4W Resistor | |
| R19, R20, R21 | 3 | 39K 1/4W Resistor | |
| R22, R23, R24 | 3 | 47K 1/4W Resistor | |
| R26, R28, R30 | 3 | 33 Ohm 1/4W Resistor | |
| C1, C5, C6 | 3 | 0.012uF Polystyrene Capacitor | |
| C2, C9, C10, C11 | 4 | 3.3uF Electrolytic Capacitor | |
| C3, C4 | 2 | 0.0022uF Polystyrene Capacitor | |
| C7, C8 | 2 | 47nF Polystyrene Capacitor | |
| C12, C13, C14 | 3 | 0.47uF Electrolytic Capacitor | |
| C15, C16, C17 | 3 | 22uF Electrolytic Capacitor | |
| D1, D2, D3 | 3 | 1N4002 Silicon Diode | |
| D4, D5, D6, D8, D8 | 5 | Green LED | |
| D10, D11, D12, D13, D14 | 5 | Amber LED | |
| D16, D17, D18, D19, D20 | 5 | Red LED | |
| U1 | 1 | LM3900 Quad Op Amp | |
| U2, U3, U4 | 3 | AN6884 Bar Graph IC | |
| MISC | 1 | Board, Wires, Sockets For ICs |
- The circuit expects line level inputs. If you connect it to speaker level, you will have to readjust the circuit every time you change the volume.
- After the circuit is connected, apply power and signal. Now adjust the pots until the corresponding group of LEDs reacts.
- Thanks to Alterac for correcting some errors on the schematic that originally appeared on this page. Read all about it in the 3 Channel Spectrum Analyzer Project thread in the forum.
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