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

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**Parts**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**- 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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