Create the bare bones of a three-channel audio-spectrum analyzer using only LM324 and LM386 ICs, and a bunch of other passive and optical components! This is a 100% analog circuit, meaning there are no LED bar-graph drivers, and no microcontroller!
As complicated as I thought this would be, this circuit is using the basic fundamentals of electronics and algebra. The only hard part is perfecting it and expanding it.
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Every part on the parts list is a part on my circuit board. If you change something, something bad (or good) might happen. Working with op-amp band-pass filters, a slight change in the values given will throw off the results. HOWEVER: You may not end up using all the parts (e.g., screw terminals) because you may not solder your LM386 set on a board. I only included them because I did solder them. And they are used for power and signal out. But other than that, nothing should be unused or traded out. You might also not use the second audio jack. It is not mandatory, but it would be silly if you can't hear the music/sound with your new spectrum analyzer. The second jack allows you to plug in your speakers while they are disconnected by the first jack.
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Yes it is. If you look at the given schematic for step 3, “Creating the display” you’ll see the OPAMP comparators and their respective voltage dividers. All you would need to do is add more OPAMPS to the 10K resistor chain.
Just reply for more questions.
Oh crud. You’re right. You will need 8; 470ohm resistors for each band (8*3 = 24) Thanks for pointing that out!
One more question, all the ICs (LM386 and LM324) are power up with V+=5V and V-=ground?
The voltage you are using may be to low. I also had a problem where 5V couldn’t get the top (red) LED’s to light up. But when I went to nine volts, it worked fine. So try upping your circuits voltage a little bit. If that doesn’t work, then adjust the resistor R10 in the bar graph schematic and/or R2, R7, and R11 in the filter schematic. Adjusting R10 increases the bargraph sensitivity, but may cause LED the leading LED’s (Like LED 1, and LED2) to remain permanently on. Adjusting R2, R7, and R11 increases the AMP sensitivity, so it outputs a bigger waveform.
I hope that helped. Thanks for trying my project! I’m glad someone actually got something out of this. :)
The amplitude of the input waveform is likely to be clipped using low voltage supplies because the amplification will be so high. The safest voltage I would recommend you go to would be 15 volts. Then clipping is unlikely. Or, to control the gain of the 386, add a stereo control potentiometer to both capacitors on both LM386’s. This will allow you to change the gain from ~20-~200.
Thanks again, i successful done that with red LED light up (i forgotten to put 56k resistor in the chain before)^^ Cheers~~
That would be the circuit common (ground) LTspice doesn’t have the favored ground symbol… :(
Thanks for answering my first question. :) I have a second question (if you don’t mind). How can I make the mono into stereo? and the pin outs for the stereo jack please. :( Sorry for asking so many questions. I’m just a beginner. :D
Technically, it is stereo. The two LM386’s amplify the audio and then mix the audio together. This is just then sent to a “mono” read out.
This circuit is VERY versatile. You can add as many bands as you’d like and adjust sensitivity. The only hard part is getting the filters to be stable and perfect to your preference.
Those resistors are to set the GAIN of each OPAMP. You can adjust their sensitivity by changing their values. Here is the formula: 1+(r2/r1) aka 1+(390k/22k)
Sorry to hear about that. From what it looks like, you either have voltage going into the signal pin, or your pull down / filter resistors are not in properly / at all.
The best thing I can tell you to do, is scrap the project, and start over from scratch. Have all the same parts (I would pick the BASS filter) and lay them in piece by piece. But with the given information, I can’t tell if the problem is in the display unit, or the filter itself.
The NPN serves as nothing more than a signal amplifier and buffer. If it were to be removed, if I remember correctly, the bargraphs may not light up all the way unless the input is cranked up to a stupid amount. But it should still work regardless.
The transistor is not a current or voltage limiter, it is in fact the opposite, a voltage signal amplifier. However, with some extra circuitry it can be used as a constant current and/or as a pass transistor in a voltage regulator. But by itself, it is a signal amplifier.
It looks like my Gmail also didn’t notify me about your comment either… But the circuit will NOT work very well without the amplifier. What it does is lowers chip count (you would probably need two more OpAmps) The amplifier does not drive a heavy load, like say an 8ohm speaker, however, since the LM324 is a slow OpAmp, driving up the gain would ruin the bandwidth.
If you want to work around it, here is something you could try:
Get two OpAmps and set them op as a x10 chain in series with each other. This will give you a x100 gain(10×10) Then add the filter stage. That should work well, but it will not work as cleanly as having a class AB amplifier before it. There will be a lot more distortion in the output.
Hello, why did you put 470 ohm resistor next to each led? Isn’t it too high? In ideal case OpAmp give us 5V, so for 3V led it give current about 4mA. Probably I dont understand, please response. Thanks
How do the outputs from each 386 connect to the filters?
Hi , I wanted to ask what is the typical output voltage peak ,from a 3.5mm audio jack. I wanted to do signal processing using ADC of a micrcontroller, i have to limit the voltage to ADC between 0 and 5 V.So how much should the gain of amplifiers be. I am designing simple basndpass filters for the same. Please help.Appreciate
I am very sorry for the late reply. I have been bogged down by highschool and college work recently.
However, typical peak output voltage from something like an MP3 player is 20mV (really low) To bring the gain of 20mV (.02V) to 2V, a gain of 100 should be used. I would use two OpAmps as 10x amps, this way minimal bandwidth is sacrificed.
Again . Very sorry I did not get to you sooner. I hope I am not too late.
Would you say this is a correct schematic for the amp?
http://imgur.com/wCbzV9Y
Yes. I just confirmed this with my description and it all checks out.
Thanks, am super excited to make this so wanted to double check!
I hope you like it. This circuit it like 3 or 4 years old now and it is still one of my favorites.
Don’t forget to have fun!
YES ,WORKING
is it possible to change the band pass filter with low pass or high pass only? the output still will be the same as yours o not?
hellow friend one confusion in your parts list 3 nos 100 pf capacitors,but in diagram that is 10 pf ,I assembled but not working
BOTH ARE SAME
i am tried this circuit many times,finally sucsess .i use bc558(2N4401),LM3915 IC & BARGRAPH
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