3 Channel Spectrum Analyzer

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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.

Schematic​

Part Total Qty. Description Substitutions 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 Notes:​ 1. 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. 2. After the circuit is connected, apply power and signal. Now adjust the pots until the corresponding group of LEDs reacts.