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 for amp


Total Qty.
R11100K 1/4W Resistor
R21820K 1/4W Resistor
R3, R14, R16, R1842.2 Meg 1/4W Resistor
R4, R5, R6322K Pot
R7, R8, R9, R25, R27, R29610K 1/4W Resistor
R10, R11, R123680 Ohm 1/4W Resistor
R13. R15, R173580K 1/4W Resistor
R19, R20, R21339K 1/4W Resistor
R22, R23, R24347K 1/4W Resistor
R26, R28, R30333 Ohm 1/4W Resistor
C1, C5, C630.012uF Polystyrene Capacitor
C2, C9, C10, C1143.3uF Electrolytic Capacitor
C3, C420.0022uF Polystyrene Capacitor
C7, C8247nF Polystyrene Capacitor
C12, C13, C1430.47uF Electrolytic Capacitor
C15, C16, C17322uF Electrolytic Capacitor
D1, D2, D331N4002 Silicon Diode
D4, D5, D6, D8, D85Green LED
D10, D11, D12, D13, D145Amber LED
D16, D17, D18, D19, D205Red LED
U11LM3900 Quad Op Amp
U2, U3, U43AN6884 Bar Graph IC
MISC1Board, Wires, Sockets For ICs


  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.
  3. 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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3 Channel Spectrum Analyzer
Wednesday, July 08, 2015 9:09:46 PM
I appreciate all of the work that went into this; could I take out the led drivers without messing with the rest of the circuit? Also, what is the value for capacitor18?
3 Channel Spectrum Analyzer
Wednesday, August 14, 2013 11:46:35 PM
Hello peoples, I was wandering if this circuit would work well with LM3915 instead of AN6884. I think it would be neat to have 10 LEDs per channel.
3 Channel Spectrum Analyzer
Thursday, May 10, 2012 9:52:04 PM
Error in my last message-- I did not meant LM3900 but those led drivers. @Audioguru: About LM3900, that can be replaced with any quad (or single op-amp). About rare led drivers concern is the same thing -- whichever comparator or opamp will do in this schematic. there are possible to make with widely available components. When replacing OP amps, just pinouts needs to be checked. And LED Drivers... its easy to convert it for opamps/comparators (in that case couple ref-level resistors needs to be added only).
3 Channel Spectrum Analyzer
Thursday, May 10, 2012 9:45:03 PM
Nice. instead of LM3900 can be any cheap quad op-amp or also quad comparator in this schematic (though with some minor modifications in schematic - resistors for ref levels).
3 Channel Spectrum Analyzer
Tuesday, December 20, 2011 10:55:15 PM
can i add another 2 channels for this project to make it 5 channels? how to do it?
3 Channel Spectrum Analyzer
Tuesday, October 11, 2011 3:12:26 PM
can i add one led on each ouput from AN6884 ? so it will be 2x5 LED in each collum is it posssible ? thanks
3 Channel Spectrum Analyzer
Sunday, January 30, 2011 7:16:37 PM
I found this reading the forum.. FROM: audioguru Posted - Jan 02 2011 : 10:18:10 PM If you add more frequency bands then you need to re-calculate the bandwidth of the existing bands to make them narrower. The "multiple feedback bandpass filter" design is in Google but uses a "normal" quad opamp instead of the weird LM3900. C18 is simply a supply bypass capacitor. Its value depends on how much ripple is on your power supply voltage. If your power supply already has a big filter capacitor or you are using a 12V battery then C18 can be from 10uF to 100uF. I think the CanaKit is the same circuit.
C18 is still missing from the parts list
Monday, January 17, 2011 8:07:24 AM
What is the value of C18? --Thanks
3 Channel Spectrum Analyzer
Thursday, March 04, 2010 7:39:06 PM
hey i got two question...im noob at this but, how do you connect audio input to this????? and what is the value of C18?? i really want to know how to add input though, like an aux cable from an ipod, or something like that.
3 Channel Spectrum Analyzer
Sunday, February 15, 2009 11:17:20 PM
firstly, thanks for this useful circuit. i saw its schematic but there is not value of the c18. i think it might be between 100-1000 microfarads
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