How to decrease distortion/noise of LM386 amplifier at max gain and volume?

Question

From my previous question, I've made LM386 amplifier and it works better than LM1458 amplifier. I've added gain and bass boost in my LM386 amplifier.

• How to decrease distortion/noise of LM386 amplifier which occurs at max gain and volume?
• Is using pin7 which is the bypass can fix the problem?
• Is there other way to improve my amplifier or do i lack something which can improve my amplifier?

additional questions:

• Since i have Bass boost, how to add treble control?
• How long can LM386 last(hours) when playing music using regulated power supply(9v)?
• What will be the effect of using 6 ohms speaker instead of 8 ohms speaker?

Edit:

• fixed postion of C6 and R4

Schematic diagram updated: (sorry for the mistake I've done, updated again.)

• after changing the position of R4 and C6, I've noticed the increase in volume. But when i changed the connection of C4 from pin4 to output(pin5) bass boost doesn't work anymore and when i put the bass boost to minimum the sound turns off also even the volume is maxed, that's why i connected C4 to the pin4. Is there a way to fix it or should i still connect c4 and pin4?

^{simulate this circuit – Schematic created using CircuitLab}

Thanks for all the comments and suggestions, and it was successful,

Answer 1

After you updated the diagram:

R4 is still in the wrong place. If you've built the circuit with R4 that way, then it is WRONG. With R4 where you have it, you lose a very large part of the volume.

Check the diagram in the LM386 datasheet and compare it to what you have built.

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1. You need to work on your circuit diagramming skills. If your circuit is built as drawn then it cannot work. Since it does work, you must have drawn the circuit wrong.
2. Distortion is to be expected if you input a large signal with high gain. The amplifier only has 9 Volts to work with. If you put in a 1V peak to peak signal with the gain at the default of 20, then the amplifier will try to put out a signal at 20V peak to peak. Since it only has 9Volts to work with, you get a lot of distortion.
3. C4 is not needed in most cases. If it is needed, then it probably needs to be larger.
4. R4 is (as Steve G has already noted) in the wrong place.
5. You've got pin4 connected as an input - it is actually the ground connection for the chip and should be connected directly to ground.

Give the number of obviously wrong things in your diagram, it would be difficult to guess what could be improved in the gain and tone control areas.

The LM386 is not rated for high power. It should be capable of making a speaker loud enough in a classroom setting (small room,) though not if you are trying to fill an auditorium with a couple of hundred students.

Answer 2

You have put R4 in the wrong place. You have put it in series with the loudspeaker which will waste more than 50% of the available output power. It should be in series with C6 down to ground (check the datasheet). Perhaps this explains why you feel that you have a lot of distortion for a given volume level.

There are a lot of things wrong with this schematic. As drawn it simply will not work.

Answer 3

Filter feedback using a 0.01 capacitor (C6) and a 10K resistor (R3) acts as an Anti-Hiss Feedback network that eliminates the hissing noise. It gives clear audio.

Answer 4

After messing about with this exact same circuit I've come to the conclusion that if you put a 10K resistor before the audio in on pin 3 as well as a 10K potentiometer You get a better sound. I've got the left and right channels both going through 10K resistors then they merge and go to the 10Kpot before pin 3. I'm using a speaker close to 16 Ohms, well it's more like 15 Ohms but quite a high impedance I've also tried with an 8 Ohm speaker and it's about the same quality.

I've also found that if you use a 1k resistor & 10uF capacitor between pins 1 and 8 then the sound is crap! you seem to get a better sound quality with a 10K Resistor & a 47uF capacitor instead!

Also On the VOUT from pin 6 I'm using a 2200uF 35V Capacitor(Just coz it's the only cap more than 24 volts and 2000uF I've got from an old HiFi. Because I've been powering this circuit with a 7V PV Cell I've also got a diode after my voltage in and a 3300uF 35V Capacitor going to pin 6 & Ground. Saves me from losing the tunes when someone walks in front of the PV cell!

All as I can say is to try adjusting the capacitor values IT MAKES SUCH A DIFFERENCE!

I've experimented with 0.1 uF 10uF 0.22uF 0.33uF 0.47uF 47uF 330uF 470uF and swapped them all around to see where I get the best audio quality. Also All of my capacitors are actually 25v or 50v and either out of a HiFi or a TV that I stripped down for parts. The HiFi ones seem to sound much better! Don't know if that's because they are of a better quality??

It seems to be more or less indestructable the little LM386-N1!!

Even after I've experimented with all the different capacitor values When you turn this little amp up too much it still distorts some what and then even when it's working more or less fine when you turn it down there's a bit of feedback. Think that's more to do with the fact that I've got more or less no clue what I'm doing, But I Still Managed To Improve The Sound Quality Of The Circuit Diagram Shown In The DataSheet By MESSING AROUND WITH IT!

You could try putting a switch in your circuit to turn the bass boost off and running the gain at 50 instead of 200. It's all the little things that Help.

I Wish I Had An Oscilloscope To See What Frequency The Feedback Is! Maybe I could adequately choose my capacitor & Resistor values better then (I ASSUME) Or at least I could Tune the circuit better!