I am having a bit of trouble trying to simulate a variation(different frequency ranges/gain for the BP filters) of this project: https://makezine.com/projects/audio-spectrum-analyzer/ I am not too experience in simulation so I am not too sure what I'm missing to get the simulation to work. I'm using multisim. Here is one of the bandpass filters that has the frequency ranges of 20-250hz. Also what exactly is the purpose of c3 and r5? I circled them. All help appreciated thanks!


  • \$\begingroup\$ C3 is a bypass capacitor used to filter out some noise. R5 is a weak pull down used to pull the line down when the transistor is off, to prevent a floating condition. \$\endgroup\$ – Passerby Apr 17 '18 at 23:33
  • \$\begingroup\$ alright thanks! Would you happen to know what im missing for my simulation to work? \$\endgroup\$ – circuit Apr 17 '18 at 23:42
  • \$\begingroup\$ No idea about multi SIM. \$\endgroup\$ – Passerby Apr 17 '18 at 23:53
  • \$\begingroup\$ Good lord: "no schematic provided because LTSpice doesn't have the 386." Then why not post the drawing from the datasheet instead of trying to "describe the circuit?" \$\endgroup\$ – JRE Apr 18 '18 at 3:50
  • \$\begingroup\$ In the comments one of the people there created the amplifier circuit and alex(creater of the project) said its correct. imgur.com/wCbzV9Y \$\endgroup\$ – circuit Apr 18 '18 at 4:16

You have supply pins connected to U2 and U3 but you've forgotten to connect them to U1.

C3 smooths the rectified voltage from the emitter of the BJT. In other words it's a cheap and inaccurate signal peak detector with C3 as the hold capacitor (go google this). R5 is needed by the BJT and also offers a discharge path for C3 in order to allow dynamic signals to refresh the display. If it wasn't there you'd have a peak-hold circuit.

  • \$\begingroup\$ like this? imgur.com/nb8xKvr I'm still getting an error \$\endgroup\$ – circuit Apr 19 '18 at 4:55
  • \$\begingroup\$ @circuit go and read the data sheet for the LM324 - pins 11 and 4 are what you should take note of and why on earth have you only wired one supply pin up - read the data sheet carefully and I think you'll notice that your one attempt had 50% chance of success as a guess but no cigar. \$\endgroup\$ – Andy aka Apr 19 '18 at 7:30
  • \$\begingroup\$ I know pin 4 is Vcc and pin 11 is ground so ive also tried grounding pin 11 and giving pin 4 a +5v VCC but that didnt work either. \$\endgroup\$ – circuit Apr 19 '18 at 16:30

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