How do I make a simple audio amplifier?

[H0R53]

How can I make a simple audio amplifier that runs off of 5v? It'd be Stereo with a small 2.5 inch sub, so I'd need an analogue low-pass filter as well for that.

 

I don't care how much soldering or components are needed, I have plenty.

[gnomik]

I recommend buying kits from china, making this stuff on your own is pain in the ass, especially the filter.

[H0R53]

1 minute ago, gnomik said:

I recommend buying kits from china, making this stuff on your own is pain in the ass, especially the filter.

 

3 minutes ago, H0R53 said:

I don't care how much soldering or components are needed, I have plenty.

 

[gnomik]

I see, but why the 5v?

[H0R53]

1 minute ago, gnomik said:

I see, but why the 5v?

USB, primarily so I can run it off a modified phone travel battery.

[gnomik]

Just now, H0R53 said:

USB, primarily so I can run it off a modified phone travel battery.

From 5v it wont get any better than this:

http://www.ebay.co.uk/itm/PAM8403-5V-Digital-Audio-Player-Amplifier-Board-2-Channel-Control-USB-Power-/263099656484?epid=818164704&hash=item3d41f62924:g:wvAAAOSweARZcZ23

[H0R53]

Just now, gnomik said:

From 5v it wont get any better than this:

http://www.ebay.co.uk/itm/PAM8403-5V-Digital-Audio-Player-Amplifier-Board-2-Channel-Control-USB-Power-/263099656484?epid=818164704&hash=item3d41f62924:g:wvAAAOSweARZcZ23

I mean I COULD do 12 but then a different battery would be required. I have one, but I'd rather use it for another time.

[H0R53]

3 minutes ago, gnomik said:

From 5v it wont get any better than this:

http://www.ebay.co.uk/itm/PAM8403-5V-Digital-Audio-Player-Amplifier-Board-2-Channel-Control-USB-Power-/263099656484?epid=818164704&hash=item3d41f62924:g:wvAAAOSweARZcZ23

Also, the speakers I plan on using are 4Ω 5W so I don't think that tiny amp will work as expected, those are for 3Ω 3W speakers.

[gnomik]

Just now, H0R53 said:

Also, the speakers I plan on using are 4Ω 5W so I don't think that tiny amp will work as expected, those are for 3Ω 3W speakers.

I have used them, they are surprisingly loud in a room. And the amp is for 4ohm 3w, not 3ohm.

[H0R53]

Just now, gnomik said:

I have used them, they are surprisingly loud in a room. And the amp is for 4ohm 3w, not 3ohm.

Oh, cool.

 

Well then, thanks, I suppose.

[gnomik]

1 minute ago, H0R53 said:

Oh, cool.

 

Well then, thanks, I suppose.

I mean, if it doesnt do what you want ~1eur is not a big loss anyway.

[Unimportant]

5 minutes ago, H0R53 said:

Oh, cool.

 

Well then, thanks, I suppose.

This might be more suited as it's 2.1 and thus has support for your woofer: http://www.benl.ebay.be/itm/DC-5V-20W-2-1-Channel-AMP-3D-Surround-Digital-Stereo-Class-D-Amplifier-Board-/361982087087?hash=item5447d04faf:g:oJMAAOSwhQhYzNsf

 

The actual output of the NS4358 chip used is 2x 3watt for left/right + 5W for the sub, which should be plenty and is about the max that can be expected from 5V/USB power.

[bowrilla]

Ehm – you either find schematics with part lists or you take some months (if not years) to study electronic engineering. It's not that trivial to come up with a proper working amp design just like that.

[GER_T4IGA]

36 minutes ago, H0R53 said:

analogue low-pass filter

I don't think you can build these in cariable sizes but I am fairly adept at audio stuff. From my understanding you would have to haul around a huge coil to make that work analogue

[gnomik]

5 minutes ago, GER_T4IGA said:

I don't think you can build these in cariable sizes but I am fairly adept at audio stuff. From my understanding you would have to haul around a huge coil to make that work analogue

For 2.5'' sub the filter wouldn't be that huge.

[H0R53]

15 minutes ago, gnomik said:

For 2.5'' sub the filter wouldn't be that huge.

It doesn't HAVE to be analogue, but it's preferred as digital filters have some loss of quality.

 

This is also going to function as part of a surround system. I already have two speakers hooked up and usable, but I want the two behind me to use as little power as possible while still remaining effective. I have a 7.1 surround output, I just don't want to spend a ton of money on a special amplifier, so each set of speakers will have its own amp.

 

A Harmon-Kaardon amplifier that I was looking at was like $800.

[gnomik]

1 minute ago, H0R53 said:

It doesn't HAVE to be analogue, but it's preferred as digital filters have some loss of quality.

 

This is also going to function as part of a surround system. I already have two speakers hooked up and usable, but I want the two behind me to use as little power as possible while still remaining effective. I have a 7.1 surround output, I just don't want to spend a ton of money on a special amplifier, so each set of speakers will have its own amp.

 

A Harmon-Kaardon amplifier that I was looking at was like $800.

Just buy used receiver from ebay, got mine for 70eur and another one for 50.

[Unimportant]

36 minutes ago, GER_T4IGA said:

I don't think you can build these in cariable sizes but I am fairly adept at audio stuff. From my understanding you would have to haul around a huge coil to make that work analogue

A simple LC filter would do the trick, say 100 μH and 100 μF would have a -3db @ 1500Hz. (cba to calculate the Q)  At the low power levels involved the inductor can be tiny, not a problem at all, but the board I linked previously has all of that on board as the chip has a deticated subwoofer channel with L/R mixing and low pass included.

[H0R53]

23 minutes ago, Unimportant said:

A simple LC filter would do the trick, say 100 μH and 100 μF would have a -3db @ 1500Hz. (cba to calculate the Q)  At the low power levels involved the inductor can be tiny, not a problem at all, but the board I linked previously has all of that on board as the chip has a deticated subwoofer channel with L/R mixing and low pass included.

Yeah, I see that. Thanks.

[mariushm]

A usb 2.0 port will only give you in theory 5v at 0.5A or 2.5 watts. With a battery bank, you're looking at best at 2-3A or 10-15 watts.

Even an almost ideal class-D audio amplifier will have about 85-90% efficiency when you're going with such low input voltage, so you're looking at anything between around 2 watts to 8-12 watts going to the speakers, if you're using 5v... but it's really difficult to pump so many watts with just 5v input... the audio amplifier IC may not be able to do it even if your battery can provide the current.

 

Audio amplifiers can output more power the higher the input voltage, so ideally you'd want to use 12v or even better, a 18-19v laptop battery (or a lithium-ion battery pack of 14-19v , 3-4  x 3.7..4.2v batteries in series)

 

Most audio amplifier chips have datasheets which also contain example circuits that you can adapt to your needs. There's usually decent amount of information. Also, for the chips that are easier to work with, you'll often find schematics online and projects made by other people.

 

You can start looking at amplifier ICs at electronic part distributors, and filter down thousands of chips until you get what you want.. here's around 6000 of them : https://www.digikey.com/products/en/integrated-circuits-ics/linear-amplifiers-audio/742

 

If you go with 5v input, you'll want chips that can start working at around 4.5v or lower and you'll probably want chips that can do 4 ohm speakers, because 8 ohm speakers will be harder to drive from 5v (so you'll have lower power)..

Then you'll want to filter the list to show only class D or better chips, because class A, B, or AB while cheaper to make are also less efficient (at around 60-70%) and in your case efficiency is very important.

 

Then you may also want to filter out chips which are very hard to solder (bga etc) and when you have a smaller selection, you'll still want to check datasheets to see how much audio power the chip can actually power at low voltage ... a chip may work from 4v to 12v and say it can do 25w, but with only 5v the chip may only be able to output 2-3 watts of audio... so that's can be tricky.

 

Here's the above link, filtered down to Class D or better amp chips which can work with 5v from USB (either less than 5.2 .. 6v, or at least 4.5v input voltage), about 500 of them : https://www.digikey.com/short/3v2cq4

 

So you can see for example there in the list, something cheap and easy to solder would be PAM8407, a 2x3w max. audio amp : https://www.digikey.com/product-detail/en/diodes-incorporated/PAM8407DR/PAM8407DRDICT-ND/4794811

 

In the datasheet, you can see a simple schematic and if you look in the datasheet on the 2nd page at 2nd graph you'll see that with 4ohm speakers the THD will be less than 0.5% at up to 2..2.5w watts, so while the amplifier IC can do 3w per channel, you don't really want more than 2.5w-ish per speaker

 

Here's another simple chip, mono up to 2.8w at 4 ohm (but you want to stay around 2.0 ..2.2w max for minimal distortions) : https://www.digikey.com/product-detail/en/analog-devices-inc/SSM2305CPZ-REEL7/SSM2305CPZ-REEL7CT-ND/1834333

You can get 3 or 4 of these and have your 2.1 system, by using some low pass filter in front of the chip or chips meant for bass.

Super simple to use, Datasheet has all the info you need.

 

And so on... you can waste hours searching for the best chip for your needs.

 

You can also buy ready made evaluation boards for various chips, sometimes they're cheaper than buying the parts separately : https://www.digikey.com/short/3v2cb2

 

 

 

 

[H0R53]

6 hours ago, mariushm said:

-Snip-

 

 

I appreciate it but I've already bought the tiny-ass chip of Amazon. That was really what I was looking for.

 

Computer speakers that run off of 5v are also what I was looking at but none had a subwoofer.