Right now, the input is coming from an ipod nano. And my output components aren't spot-on (1M, 4.7k, 10nF), but the quality is good enough. Its just not very loud.
So I decided to try my hand at building a LM386-based amplifier. I've used the "Amplifier with Gain = 20 Minimum Parts" design from page 5 of the datasheet:
The trouble is that it still isn't loud enough. When I say loud enough, imagine trick-or-treating. It should be as loud as a typical eight-year-old in full-on shakedown mode.
I don't have a great deal of experience building LM386 amps, so I figure that my problem falls into one of two categories. Either I've built the amp wrong, or the LM386 just isn't up to the task.
So, if anyone here have any experience with LM386 amps, I'd like to know if they can be used for this purpose?
You are just driving it with 5V power supply? That will limit the power you can generate.
Pmax = (V x V)/R, so 25/8 = ~3W max no matter what.
There are some limits on voltage swing due to the fact that transistors are involved.
Reading page 2 of the datasheet, with a 6V supply, 8 ohm load, typical output is only 325mW.
If you want it louder, you need a higher voltage power supply - and a more capable speaker. And even then you can only expect 1W out.
This part and that speaker are not up to the task of overcoming an excited 8 year old.
http://www.diodes.com/datasheets/PAM8403H.pdf
See page 2 - with 8 ohm speaker you are limited on output power. 4 ohm can output more.
So that combo might be acceptable.
A lot will come down to the speaker enclosure, and its unlisted sensitivity.
This setup, driven from PWM from arduino, is quite loud (ignore the switch at the top, it just allows the 68 ohm resistors to in series or parallel).
Its what I use in the boxes at my 2000 sq ft fencing club.
It drives this 4 ohm 90dB sensitivity speaker. http://www.mpja.com/4-Ohm-Mini-Speaker/productinfo/14618%20SP/
You can see the speaker here, the MOSFET and two blue 68 ohm resistors can be seen to the lower left of the speaker.
12V power makes all the difference.
(the boxes had a bunch of small holes drilled out in front of the speaker as a grill, this pic was more of a component test fit)
Maybe, maybe not. 3710 are not really spec'ed as logic level devices, the 3707 was selected because it had good numbers at Vgs of 4.5V.
Sensitivity – The sound pressure level produced by a loudspeaker in a non-reverberant environment, often specified in dB and measured at 1 meter with an input of 1 watt (2.83 rms volts into 8 ?), typically at one or more specified frequencies. Manufacturers often use this rating in marketing material.
So generally, higher sensitivity = louder sound. Those little mpja speakers work quite well. I havre 6 scoring machines, my wife is always telling me they are too loud. I think they sound great - programmed to make a 2-tone warble kind of like a cell phone, using 2 notes from the Tone library. Not all the same, makes an interestint racket when all 6 are powered up at once from the same power strip.
But what you've shown in the schematic is a Class B amplifier with a seriously large threshold. It'll take much higher than line levels to get a meaningful output, and it will be highly distorted.
You can run an LM386 with a heat sink, use a 4 ohm speaker like the one suggested, and run the LM386 with the gain setting capacitor added and from higher voltage. That will likely get you loud enough. You have the parts, try it.
A reasonable way to tell speaker sensitivity is magnet size. Larger magnet, higher efficiency, louder speaker.
Me? I put in a 0-5V burst of tone output, the sound out is very nice, nice & loud in my 2000 sq ft fencing club. No problem at all hearing it. If it's distorted, it certainly helps it sound better. Two tones, like B4-A4-B4-A4-B4-A4-B4, lasts about 1 second, maybe 1.25 second when a touch is scored - and with beginners, a lot more often as they get over the newness of it all Just set it up by ear to what sounded good to me - vs USFencing requirement for some fixed pitch that lasts for 2 seconds, some very obnoxious headache inducing blare of sound.
Minimal components, no heatsink. Been running 6 of these since Dec 2010/Jan 2011, no issues at all.
But all you wanted is a loud tone and are using a 0 to 5V square wave. He is building a voice altering box, with the current input from an iPod. Presumably he wants the voice to be understandable.
Just set it up by ear to what sounded good to me - vs USFencing requirement for some fixed pitch that lasts for 2 seconds, some very obnoxious headache inducing blare of sound.