Hello, I am trying to build a vumeter with LM 3915. The LM 3915 works pretty well with high volume but i mostly i listen music with headphone at low volume. At this case the only 2 led with light up.
I add an LM 386 as an amplifier and at full volume of that amplifier the led the light up as expected.

What i want to achieve is a kind of automatic process. When the volume is low the amplifier should make it high and opposite when is low the amplifier should normalize to not let leds stay only all on.
Also i hear some noise on headphone I try to add an 1N4007 diode but with that installed no audio passing through.
Thank you.

 

Most of my internet is down so I can't see if the old LM3915 is obsolete now.
I made a Sound Level Indicator circuit 14 years ago with an LM3915.
Yours has the LEDs fairly dim at 4.8mA (due to the value of R1) but mine is very bright at 26mA for each LED.
Your LEDs are even dimmer because you do not peak detect the signal which the datasheet says produces a dim blur.
Mine uses my version of the peak detector rectification and momentary hold recommended in the datasheet for each LED to be bright.

The LM3915 has 10 steps of 3dB for a full range of 30dB which is not much. 30 years ago I made a VU meter with two LM3915 ICs in series for a range of 60dB shown on 20 LEDs. In the newer circuit I added a second peak detector that changes the voltage feeding the voltage on the pin 6 resistor ladder which reduces the sensitivity 10 times for loud sounds. Then the range is 50dB (a pin dropped to loud sounds).

Your noise (hiss) is because the LM386 is a cheap speaker amplifier with it set for very high gain. You should use a low noise audio opamp as a preamp and the LM386 at low gain. Also the 12V power on your circuit should have a 0.1uF ceramic capacitor plus a 220uF electrolytic capacitor.

Here is my circuit with an electret mic input and a Ni-Cad 9V battery (now it is Ni-MH) trickle-charging all the time.

 

So you don't want a real level indicator......you want a display. Not familiar with that chip. Is there a way to get it to display the average for high headphone use, and then display the peak for low headphone use?

 

Not familiar with that chip. Is there a way to get it to display the average for high headphone use, and then display the peak for low headphone use?

The chip itself can't do that. Additional circuitry would be needed.

 

https://en.wikipedia.org/wiki/Phone_connector_(audio)#/media/File:Jack-plug--socket-switch.jpg

"A pair of phone connectors: A plug (right) is inserted in a socket (jack, left) Note the flat open contact spring parallel to and inside the tip contact spring. When the plug is removed, those contacts close to connect a circuit; such a connection is said to be "normal". Inserting the plug connects its tip to one part of that circuit instead.”

Maybe you can use that switch to determine how much volume goes to your Vu meter.

 

I was correct. the LM3915 is obsolete and not made anymore. There are probably many defective ones sold on ebay.

There is not much different between the average level and the peak level of music or speech (maybe 10dB or 15dB?) so it is not worth automatically switching between an average detector and a peak detector.

Your schematic does not show your headphones jack so is it at the output of the LM386 and having its level turned up and down together with the LM3915 level? If so, then that is your problem. When you turn down the level then the LM3915 shows almost nothing. When you turn up the level then the LM3915 shows all LEDs on all the time. Simply connect the input of the LM3915 to the audio source with its own volume control.

Try adding a peak detector to your circuit, it makes the LEDs look much better.
I hope your LM3915 does not get too hot since it is heating a lot when all LEDs are lit since your 12V supply wastes about 10V in the LM3915 making heat. Mine uses a 9V supply and a 10 ohm 1W resistor to share the heat.

 

The voltages on pins 4,6 sets the Lower and Upper range to light the LEDs, lowering pin6 voltage will work better on low audio signals,,Note your circuit is drawn wrong!!




otherwise you need an AGC audio amp.

 

I was correct. the LM3915 is obsolete and not made anymore. There are probably many defective ones sold on ebay.

There is not much different between the average level and the peak level of music or speech (maybe 10dB or 15dB?) so it is not worth automatically switching between an average detector and a peak detector.

Your schematic does not show your headphones jack so is it at the output of the LM386 and having its level turned up and down together with the LM3915 level? If so, then that is your problem. When you turn down the level then the LM3915 shows almost nothing. When you turn up the level then the LM3915 shows all LEDs on all the time. Simply connect the input of the LM3915 to the audio source with its own volume control.

Try adding a peak detector to your circuit, it makes the LEDs look much better.
I hope your LM3915 does not get too hot since it is heating a lot when all LEDs are lit since your 12V supply wastes about 10V in the LM3915 making heat. Mine uses a 9V supply and a 10 ohm 1W resistor to share the heat.

Yes i use cheap parts 5 pieces for 1$.
Main audio passing through LM 386 and the output of 386 connect to input of LM 3915. LM 386 control the volume.

I haven't heard for a peak detector i will try that. The chip stay very cold normal temperature, never become hot.

 

You are lucky that the high value for your R1 reduces the LED currents to only 5mA each. Then with 2V red LEDs and your high 12V supply, when all 10 LEDs are lit then the current is 50mA and the heating is (12V - 2V) x 50mA= 0.5W. If your LED currents are 13mA then on a warm day the chip will be at its maximum allowed temperature.

Since you do not increase Vref by using pin 8 then your pin 8 should be connected directly to ground with your R2 removed.