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help with vu meter and microphone

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fkuk

Member
hi

what im trying to do is make vu meter (lm3916) work with a microphone

but ive noticed that the microphone does not give enough voltage out, so i got a power amplifier (lm386) connected the mic to the amp and then to the vu meter

but all the lights light up

what am i doing wrong is it the amplifier?
if so how do i get it to work

thanks
 

audioguru

Well-Known Member
Most Helpful Member
You forgot to attach your schematic so we don't know what is wrong.
We also need to know if your microphone is an electret type or a dynamic type.
 

fkuk

Member
9224-Picture002.jpg
 

audioguru

Well-Known Member
Most Helpful Member
The input pin 3 of the LM386 amplifier is supposed to be at 0VDC. Yours is being forced up to +2V to +4V by the 1k resistor that powers the mic so the output DC voltage of the LM386 amplifier will be as high as it can go (and it will not amplify) which is about +3.8VDC.
Add a 0.1uf coupling capacitor from the mic to pin 3 to block the DC from the mic but pass the signal. The inputs of the LM386 already have resistors to 0V.

The input pin 5 of the LM3916 is a DC voltmeter. All LEDs are off when it is 0VDC but yours is at about +3.8V so all the LEDs are lighted.
Add a 0.1uf coupling capacitor from pin 5 of the LM386 to pin 5 input of the LM3916.

The input pin 5 of the LM3916 is a PNP transistor that needs a 100k to 1M resistor to 0V to have the LEDs turned off without a signal.

Your LEDs will be very dim with the resistor values you have chosen for the LM3916.

Your 5V regulator probably will not work properly and the LM386 and LM3916 also will not work propely without the important capacitors shown on the datasheet of the regulator.

The LM386 probably will not work properly without the inportant 10 ohms in series with 0.05uF (0.047uF) from its output to ground to prevent it from oscillating. Look at its datasheet.

Why is your supply voltage as high as 12V and/or why is your regulated voltage as low as 5V? The difference will just make the regulator hot.
 

fkuk

Member
omg you sir are a genious it works kinda i need a higher gain though i have to play music at my phones highest setting and hold it point plank from the microphone

i want to ask you to make a adjustable gain would i connect in series a 10µf cap with a varible resistor? and the varible resistor will be 2kΩ ish
 

audioguru

Well-Known Member
Most Helpful Member
Why don't you look at the datasheet for the LM386 amplifier? It shows a gain of 20 and a adding a capacitor boosts the gain to 200. Then simply add a volume control or add a resistor in series with the added capacitor.

The datasheet shows a circuit with a gain of 50. It has a 10uF capacitor in series with a 1.2k resistor between pin 1 and pin 8.
 
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