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Circuit Diagram Experts Needed. Thanks. Answered

Picture of

(I posted an image)
I found this circuit in an book of mine because I wanted to build a VU meter. I only want to simplify this circuit. I don't need sound coming out of the VU meter; so I could have just remove the speaker and be done with it. But... is there anything else in the diagram that is only related to the speaker in which I could remove? All I need from this circuit is the led reacting to the audio input like a VU meter. Eliminating unnecessary parts will help me make it smaller. Thanks!

Helpful things to know about diagram:
Ignore R1, C5, U2.... those are just references to another diagram.
324 is an Operation Amplifier IC (there is only 1)
546 is an Audio Power Amplifier IC (there is only 1)
the Si is a silicon diode
the VR is a 50k ohm control volume (potentiometer?)
6 volts going in
Ignore the funny looking earphone, thats the audio input instead.

I posted one General Image and 4 close up Images.
Any other question about the diagram feel free to ask.

Once Again Thank you for helping a newbie.

5 Replies

mathewsBest Answer (author)2009-08-13

Op-amp (U2) is probably an amplifier to make the signal from the input louder for the loudspeaker. You will need this.

U1 is an LM324 quad low power amplifier and compares the output to the loudspeaker with the reference voltages defined by R3 to R10. When this threshold is reached or exceeded, the LED goes on. You will need this.

Also, do not ignore the component names, they are an important reference to the individual components, and they apply to THIS diagram.

There are 9volts on the supply.

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Dmxspider (author)mathews2009-08-13

Oh, Thanks! I'll make note of that. So all thats left that i think is for the speaker only is the 100uf cap and perhaps the silicon diode? if i removed that pin 4 of U2 would be empty and the wire would stop at R2. Would this be Okay? removing a couple components is still something. :) Thanks again!

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mathews (author)Dmxspider2009-08-13

The 100uF capacitor stops DC flowing out. The diode rectifies the output to feed it to the u2 comparators. Pin 4 and 11 on u2 are the power supply. If this image is in a book, it is going to work. Why do you want to change it?

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Dmxspider (author)mathews2009-08-14

Oh then the answer is simple, remove only the speaker. Theres nothing else i can remove thats ONLY related to the speaker. Thank you, you were very helpful. Thanks

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Re-design (author)2009-08-13

I'm not that good at disecting circuits yet but if you just want to make a vu meter look at this link https://www.instructables.com/id/LM3915LM3916-VU-Meter/ .

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