LM386 Distortion > I'm in awe

[ChrisHansen2Legit2Quit]

https://www.google.com/search?q=lm3...AA&biw=1280&bih=800#biv=i|0;d|Sysg93pFat16RM:

I'm frustrated. This schematic can't get any easier.

You have to turn the POT up at least 70% to hear anything, & it's so distorted that you can barely make out what song is playing. Very quiet too. I'm at the mall & I had to leave because I couldn't hear the music (or noise, lmao) coming out of the loudspeaker.

I've swapped IC's, swapped the 1" loudspeaker for my headphones, swapped components, etc. Still very quiet. Still full of distortion.

https://www.youtube.com/watch?v=hwPg8RT82d8

I know that's probably not going to help, but there it is.

Suggestions?

The 10uF cap from pin 1 to 8. I guess many people remove that. I could not make out any difference when it was in or when I took it out.

Thanks.

D

 

[Audioguru]

The manufacturer of the LM386 assumes that you know it will oscillate at a radio frequency and produce lots of distortion when it is built on a breadboard like you have and when it has no supply bypass capacitor that you do not have.

Build it on a compact pcb with a supply bypass capacitor and it will sound excellent.

A 1"speaker is a joke, isn't it?

 

[ChrisHansen2Legit2Quit]

The manufacturer of the LM386 assumes that you know it will oscillate at a radio frequency and produce lots of distortion when it is built on a breadboard like you have and when it has no supply bypass capacitor that you do not have.

Build it on a compact pcb with a supply bypass capacitor and it will sound excellent.

A 1"speaker is a joke, isn't it?

Not if they're Scanspeak Illuminators

I have yet to etch. I'll post up soon. I'm going home to perfboard it.

 

[Audioguru]

A 1" Scanspeak Illuminator is a tiny little tweeter with almost no sound below 400Hz. They are 4 ohms which is difficult for an LM386 to drive.

I make almost everything on stripboard. The perforated copper strips form half of a pcb and the parts and a few short jumper wires form the other half.
I design the layout to be very compact like a pcb and I cut the strips of copper with a drill bit. Then each strip can be used for many parts of a circuit.
Here is an example:

 

[ChrisHansen2Legit2Quit]

***I am using a stereo jack for this amplifier.

Could that be the issue?

 

[Audioguru]

***I am using a stereo jack for this amplifier.
Could that be the issue?

The LM386 amplifier is for a single channel, not stereo. Two amplifiers are needed for stereo. It is designed to drive an 8 ohm speaker but it can drive 4 ohms at a lower output level then it gets hot. If you have one LM386 amplifier trying to drive two 4 ohm speakers in parallel then its output will be very low and it will get very hot and might become damaged.
Please post your schematic showing the output load impedance and the supply voltage.

 

[ChrisHansen2Legit2Quit]

https://www.youtube.com/watch?v=GYV95Fs6UGE

Please take a look at the video. It's short!

The amplifier is functioning.

I don't think I have it quite right yet. I should be able to at least get away with a 10uF for Gain on Pins 1 & 8. When I try, the amplifier is just as loud (without distorting. Of course it gets louder!) as if the capacitor were not there.

Still getting a small amount of crackling. Not sure how to filter the rest out?

When I disconnect the input source (the audio jack from my tablet), I can hear KTOE Mankato, which is the local radio station.

Ground/floor noise is kind of bad. The continuous "chhhhhhhhhhhhhhhhhhhhhhh" noise you get when nothing is playing. The noise you'd get when you turn your receiver to MAX & are not playing any song.

Thanks!

 

[Audioguru]

The LM386 has a frequency response over 2MHz so it probably oscillates when the amplifier is built on a breadboard. Use a compact pcb or stripboard instead.
The 10 ohm resistor and 47nF (0.047uF) series circuit at the output is important to prevent high frequency oscillation. Since you replaced the 10 ohm resistor with a capacitor then you are completely shorting high audio frequencies which is bad.

The 10uF capacitor between pin 1 and pin 8 boosts the gain 10 times so the noise (hiss) is amplified and the volume control must be turned way down to prevent clipping distortion (crackling). Do not use this capacitor if you do not need more gain.

Your 9V battery is a very old carbon zinc type that has a low capacity. It is probably about 6V. Then the maximum undistorted output power is only 0.2 Watts into 8 ohms which is almost nothing. A cheap clock radio produces 3 times more power. If you use a brand new 9V alkaline battery then the maximum undistorted output power of an LM386 into 8 ohms is 0.45W which sounds only a little louder than 0.2W. Ten times the power sounds twice as loud.

If the volume control is turned up more to try to get more than only 0.2W with your old battery then the amplifier will be clipping and producing severe distortion.

Shorting the left and right output channels on a player can destroy its output circuits. Two series resistors can be used to mix the two channels together safely.

A simple calculation for the reactance of the output capacitor shows that 47uF into 8 ohms cuts the frequency of 426Hz. Lower frequencies (all bass sounds) are cut more. 470uF into 8 ohms cuts 42.6Hz which is a fairly low bass sound.

A speaker MUST have a properly designed enclosure to prevent low frequency sounds at its rear from cancelling low frequency sounds at its front.

EDIT: after seeing your video again I saw that the speaker is only 4 ohms so the maximum undistorted output power with your old battery is only 0.1 Watt which is almost less than nothing. The low frequency cutoff frequency caused by the output capacitor is doubled. 47uf cuts 852Hz and frequencies below (all bass and many midrange sounds). 470uF cuts 85.2Hz (upper bass sound) and frequencies below.

 

[ChrisHansen2Legit2Quit]

10x the power is only 2x as loud?

I read about this in a book called Infinity. How nature has built logarithmic scales into our senses (hearing included). As to why, I do not know. I can only assume it has to do with the vast amount of "data" reality possesses, & our brains not being to handle it all. So, our brains (or nature) has learned to take snip bits of it. For example, the naked eye can take in over a million different shades, but that doesn't mean that shade 2 is 2x as dark as shade 1.

So why the 3db increase? I am not sure. I think nature has built that into us to protect our (vital) ability to hear. If 2x the power meant 2x the dB increase, then half of us would probably be walking around with blown ear drums.

What do you think? This is a purely philosophical question. But what fun is science without asking a why question.

I am currently using an alkaline 9V. I like to think of amplifiers as a 3rd party. You are "taking advantage" of the supplied power via 3rd party source (like a battery). So why stop at 9V? Well I figured it out by wiring two 9V batteries in series. At 18V, I started hearing a tone of some sort. Then the tone started to move up in frequency. Then I heard nothing. I reached down to touch the IC & almost burnt myself.

There must be limit to how much the IC can handle, or that circuit if you will.

When you amplify a signal, is it the voltage that matters or the current?

Would it make a difference if I was using a linear, log/audio, or a standard POT?

 

[Audioguru]

10x the power is only 2x as loud?

My amplified computer speakers have a 9VAC/1.1A transformer that has a maximum output of 9.9W. It drives a woofer amplifier and two satellite mid/tweeter amplifiers. The maximum undistorted output is about 5.5W and it is fairly loud. The remaining 9.9W - 5.5W= 4.4W is heat.

My home stereo produces a maximum undistorted 70W per channel which is 140W total and it is a little more than twice as loud as my computer system.

At 18V, I started hearing a tone of some sort. Then the tone started to move up in frequency. Then I heard nothing. I reached down to touch the IC & almost burnt myself. There must be limit to how much the IC can handle, or that circuit if you will.

The datasheet for the LM386 shows an absolute maximum allowed internal temperature of 150 degrees C which is very hot. If the ambient temperature is 25 degrees then its maximum amount of heating power is 1.2W because the surface area of its case cools it a little.

A graph in its datasheet shows its output power vs its heating. With a 4 ohm speaker its maximum allowed supply voltage is only 12V. Its maximum undistorted output will be 0.3W. With a 9V supply its maximum undistorted output is the same but its heating is less.
It works more efficiently with an 8 ohm speaker.
It has a maximum undistorted output of 0.6W into 8 ohms with a 12V supply. Then its heating is 0.8W. With a 11V supply its maximum undistorted output is the same but its heating is reduced to 0.7W.

When you amplify a signal, is it the voltage that matters or the current?

Both because Power = voltage times current. But the amount of power wasted by heating must also be considered.

 

[ChrisHansen2Legit2Quit]

Just thought I'd post an update.

There's a "bass boost" option for this circuit. It's a simple 10k resistor in series with a 33nF capacitor from Pins 1 to Pin 5.

I mentioned earlier I was having difficulties with floor noise. Anyways, that little bass boost modifcation made a dramatic improvement. I don't necessarily care about the boost in lower frequencies, it's just that the floor noise is (almost!) all gone.

 

[Audioguru]

The "bass boost" parts for an LM386 amplifier do not boost anything. They simply reduce the gain (+19dB) at higher frequencies and bass frequencies are at the same gain (+26dB) as before. The "hiss" is at the higher frequencies that are reduced.

 

[ChrisHansen2Legit2Quit]

...oh dang

Any alternatives to reduce hiss other than the "bass boost"

Did you come up with this schematic, lol?

 

[Audioguru]

Any alternatives to reduce hiss other than the "bass boost"

The LM386 produces hiss because it is cheap. It sounds pretty good but it is not high-fidelity.
The LM3886 high-fidelity amplifier IC has a lot more power, very low distortion and very low hiss.

Did you come up with this schematic, lol?

What schematic??

 

[ChrisHansen2Legit2Quit]

The lm3886t or lm3886tf?

Parts express carries both. I just ordered a dozen of the hiwave bmr 12's for a line array. They are 8 ohm so ill see how they sound off the 386. I would like to build a tube!

 

[Audioguru]

The lm3886t or lm3886tf?

I have never seen an LM3886TF that is in an "isolated" case. Maybe it will have poor cooling but the datasheet does not say anything about it.

I just ordered a dozen of the hiwave bmr 12's for a line array. They are 8 ohm so ill see how they sound off the 386. I would like to build a tube!

Another tiny speaker with no bass. In a 1.6 liter enclosure it has a peak at about 120Hz, a -6dB dip from 250Hz to 2.5kHz and very low output above 15kHz.

 

[ChrisHansen2Legit2Quit]

I have never seen an LM3886TF that is in an "isolated" case. Maybe it will have poor cooling but the datasheet does not say anything about it.


Another tiny speaker with no bass. In a 1.6 liter enclosure it has a peak at about 120Hz, a -6dB dip from 250Hz to 2.5kHz and very low output above 15kHz.

When you find a speaker capable of playing the whole spectrum, let me know. You can do this^ with every driver & you know that. There is no such thing as a perfect speaker. They simply do not exist.

I have an SLS 6 for sub duty. I will cross accordingly. The bmr's are for my desktop & will be on axis enough to get away w/out using tweeters

 

[Audioguru]

When you find a speaker capable of playing the whole spectrum, let me know. You can do this^ with every driver & you know that. There is no such thing as a perfect speaker. They simply do not exist.

I have an SLS 6 for sub duty. I will cross accordingly. The bmr's are for my desktop & will be on axis enough to get away w/out using tweeters

My computer speakers have 4" drivers with magnets huge for little speakers. They are in slightly ported pretty big enclosures. They produce sounds from about 70Hz to 15kHz pretty well. Their power transformer is 12VDC/1A so each speaker gets about 3.2W.
I do not like to hear high frequencies being modulated by low frequencies so a woofer and a tweeter should be used.