Really Simple High Quality Audio Amplifier

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kucomp
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Really Simple High Quality Audio Amplifier

Post by kucomp » Sat Apr 24, 2010 2:22 pm

Hi, haven't posted here in a while. Thought I just wanted to share my design for what's probably the simplest amplifier one could build. I got a 60 watt 6" inch speaker and wanted to build an amplifier to make use of it. This was my first time working on an analog circuit, so I searched on Google for schematics of simple amplifiers, a majority of them using the LM386. So I bought some LM386's and to my dismay, it didn't really sound good (noise increases as you crank up the volume) and it wasn't loud enough.

So I searched around for other amps and stumbled upon the TPA6021A4 manufactured by Texas Instruments. What I liked about it is that it comes in an DIP package so I could just breadboard it. So I tried it out and to my surprise, it sounds really awesome. My design is extremely simple, is louder and the sound it generates is really crisp. All you need is two capacitors (0.47uF electrolytic) and a TPA6021A4 integrated circuit.

Image

Some things to note, the circuit runs off only 5V. Pin 7 must be attached to the ground of your input signal, not the power supply (I think all 3.5mm jacks have a left, right and ground. That's the ground I'm talking about.) Also, you don't actually need a 0.47uF. I think any capacitor close to 0.47uF would do. In fact, I didn't have an 0.47uF capacitors, so I just hooked up a 3.3uF and a 1.0uF in series to get 0.77uF which is close enough. And finally in the schematic, Pin 18 is for controlling the volume. I just hooked it up to 5V for maximum volume, but you could place a 100K pot to control the volume.

The TPA6021A4 is about double the price of an LM386 (Digikey), but the TPA6021 supports stereo audio. To hook up another speaker, you would only need attach another capacitor to pin 4, tie pin 3 to high, tie pin 5 to the input signal ground and pins 2 and 20 to your right speaker.

If you want to build this amplifier, tell me how it goes. :)

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MrAl
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Re: Really Simple High Quality Audio Amplifier

Post by MrAl » Sat Apr 24, 2010 2:36 pm

Hi there,


This sounds pretty interesting really. I dont really need an audio amp right now, but i like to keep up with the new parts just in case i need one in the future for something.

Just to note, if you have two LM386 packages you can run them in 'bridge' configuration, which gives you more volume.
One is driven normally and the other is driven inverted so that the differential signal getting to the speaker is actually
twice as high in voltage as with only one amp. Drawback is you can not connect one speaker terminal to ground,
but have to hook one speaker terminal to the output of one LM386 and the other terminal to the output of the other LM386.
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kucomp
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Re: Really Simple High Quality Audio Amplifier

Post by kucomp » Sat Apr 24, 2010 2:50 pm

Thanks for the tip MrAl. By bridge configuration, is that like one LM386 in series to another LM386 (the output of one LM386 feeding into another)?

The main problem I had with the LM386 is that there was a lot of distortion (hisses and scratches) in the sound. I had the amp hooked up to my laptop, so as I cranked up the volume on my laptop, the LM386 then started to produce a lot of scratchy noise which is not apparent with the TPA6021A4. If I hook up two LM386's in bridge connection, will there be more distortion?

I tried adding more capacitors in parallel to the speaker to reduce the noise, which it did, but it also makes the sound output sound more weird and funny. My knowledge of analog is not strong (I'm majoring in computer engineering), but I think the capacitors are cutting out or eliminating some of the audible frequencies which is why the sound output sound's weird.

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MrAl
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Re: Really Simple High Quality Audio Amplifier

Post by MrAl » Sat Apr 24, 2010 3:33 pm

Hi again,


Well actually to connect two LM386's in bridge configuration you connect one speaker terminal to
one LM386 (call that IC1) and the other speaker terminal to the other LM386 (call that IC2).
That means the speaker is driven from the two outputs only. One LM386 is driven into it's
non inverting terminal, and the other LM386 is driven into it's inverting terminal (with the audio).
In effect, they are sort of in parallel, except one LM386 has to invert the audio.
The reason this increases the volume is because the voltage getting to the speaker is effectively doubled.

I didnt like the distortion of those LM386's too much either. I dont know if the bridge config
will be better, probably not, but you may want to try it just for the heck of it.

Here is a rough drawing:
Image
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Robert Reed
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Re: Really Simple High Quality Audio Amplifier

Post by Robert Reed » Sat Apr 24, 2010 3:53 pm

You say you wanted to take advantage of your 6"x 60 watt speaker. Did that mean you wanted to pump near the max power into it. This chip will only give about 1.5 watts into a 4 ohm load or worse yet <1 watt into 8 ohms (levels to keep THD to <0.5%).
BTW, both outputs are already bridge type amplifiers in this chip, but those two outputs can then again be bridged if you run mono operation and you can quadruple the power to the speaker (6 DB) by doing this. However thats still a far cry from your speakers max power if thats one of your objectives!

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MrAl
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Re: Really Simple High Quality Audio Amplifier

Post by MrAl » Sat Apr 24, 2010 4:34 pm

Hi Robert,


Oh yes, i have to agree that there are much better chips out there if one wishes to get up to somewhere near 60 watts.
Perhaps it would be wise to look into these chips.
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kucomp
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Re: Really Simple High Quality Audio Amplifier

Post by kucomp » Sat Apr 24, 2010 4:36 pm

@MrAl: Thanks, I'll try doing that.

@Robert Reed: When attaching the speaker straight into my laptop, the speaker isn't loud and sound is very faint, so I decided to build an amp. Yeah, I know that the chip is only 2 watts and this confuses me since the speaker is rated at 60 watts, but the amplifier is already extremely loud and extremely simple thus accomplishing my main goals. I'm not sure if my theory is right, but the power rating on the speaker has little to do with how loud the sound is right? If I understand physics right, the more power, the more heat, since more work is done to convert electrical energy to sound. Speakers heat up, so the power rating on the speaker tells how much power the speaker can take before heating up too much and exploding? I'm sorry if these questions sound dumb, but I've never taken any analog courses yet in college.

EDIT: I've already gotten 25W chips from Texas Instruments. I don't think I'll be using them though, because my amp is already loud enough for me (and for all the people in the dorms :)). Heh, I'm too afraid to see what happens when I use a 25W amp.

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Re: Really Simple High Quality Audio Amplifier

Post by Robert Reed » Sat Apr 24, 2010 8:51 pm

Well you are on the right track. The speaker is rated at 60 watts by the Manufacturer, but theres a lot of marketing BS involved here. Drop down several posts and read "Home Audio Specs" and you will see what I mean. Any how a couple of watts can sound pretty loud in the right locations and if that suits your needs, there is no sense in increasing that volume. If you pumped a steady 10 watts out of an amp and then increased that power to 30 watts, you would only hear a small difference, as the human ear compensates for loudness by desentisation. As I have said before - Loud is Loud and if you make it louder, its still only Loud. I checked my home stereo system for background music level, such as when you are listening but doing other activitys and believe it or not, one quarter watt was a very pleasant level.

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MrAl
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Re: Really Simple High Quality Audio Amplifier

Post by MrAl » Sun Apr 25, 2010 3:40 am

Hi again,


Yes sometimes it's amazing how little power we need sometimes for audio to sound ok.

Also not to overlook are headphones. I use headphones a lot mostly because they sound better than speakers.
If you get a decent pair of headphones you can listen as loud as you wish and not bother anyone else, and you
dont need an amplifier either.
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Re: Really Simple High Quality Audio Amplifier

Post by Robert Reed » Sun Apr 25, 2010 7:56 am

MrAl
Yea, I agree with that plus the stereo effect is fantastic. Looks like a pretty nice chip all in all, but I wonder how the availability is on it.

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