Freestyle Amplifier




Posted in TechnologyAudio

Introduction: Freestyle Amplifier

About: I like electronics.

Just thought I'd share a few pic's of my latest amplifier project. It utilizes a TDA2004 and has a cool stereo 10W per channel. It runs off 12V and, amazingly, it works!

The sound quality is pretty good, but there is the tiniest amount of hum present. Not enough to annoy me, though.

Please comment.



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    Hi, any chance you could draw a circuit diagram with the list of used parts and components? Would love to have one for my small PC project :0)

    1 reply

    maaf aku awam tapi aku hobby bolehkah aku meminta skemanya sebab aku sulit mengaplikasikannya secara manual,terima kasih aku tunggu ya.

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    ini gue dapat dari google, document daripada unisonic tech, kamu juga boleh download melalui ini

    Those 2004 series chips have a LOT of distortion. They are in a lot of cheaper car stereos and I've seen them in a lot of amplified computer speaker sets. If you want a REALLY good chip amp, the LM4780's are about as good as they get, with total harmonic distortion down to about .001. They will eat a lot of power though, and need really smooth power to reduce the hum you spoke about. Look up "gainclone" amps on google, and you can find some interesting approaches to direct wiring. The shortened paths are supposed to give cleaner sound if you use good enough components. Nice ible!

    10 replies

    I looked at the datasheet for that chip. Any idea why there are so many connections for + and -? The rest i get.

    Heh. Yeah. And I smoked a few chips before I learned this. Single ended amps need DC power measured above and below 0 volts. That is why they say +/- 18v or whatever. Look at the "Typical Application" graphic, and you will see where the plus' and minus' go. All plus' I think go to positive DC, but some of the minus' go to ground and at least one goes to minus DC. The DC inputs are 1 and 4, and the audio inputs should be pins 7 and 8. Pin 8, the minus input, is "inverting", which is used for ground reference when you use the + input. Pin 7 is the "Non-inverting" input, meaning the output will be in phase with the input.

    Take a look at this site for more detailed instructions.


    I don't really know what negative voltage is......

    Ahh. Now that I think of it, that's how I smoked me first chips. Imagine if you connect two 12v batteries in series, the positive from one battery to the negative of the other. Your zero volts would be taken from the connection between the terminals, positive would be taken from the battery who's negative terminal is connected to the other battery, and you negative voltage would come from the free terminal on the battery who's positive terminal is connected to the other battery. The diff across the series is 24v total, but from either end to the center is only 12v; one side is +12 and the other is -12 from the center. That gives the amp the push/pull it needs. Now, how do you get this from a transformer you ask? You can use two batteries of course (or 4 9v batteries in series for +/- 18v). But if you gut an old amplifier and test the transformer, you will find one of the following: either three output wires where you see + & - AC voltage referenced from a center leg. Or, you might see four wires, where you have like two 18 or 24v AC legs that you tie together like the batteries above to get +/- 18 or 24v AC. I have also seen two sets of three wires where one set was +/-24v and the other was +/-18v, each with it's own center leg. If you connect these to a bridge rectifier, it will convert them to DC, but it will be too noisy to use for an amp. You need to bridge a pair of 10,000mF caps between each DC leg and the center. Practice this with little transformers that are not big enough to weld your tools together. Big audio transformers have hundreds of watts and are dangerous. The last configuration you may run across is just two legs with no center reference. Lets say you have 40v AC output from a transformer and you want +/-22v DC for your amp. Hook the two output legs from the tranny to the AC poles of a bridge rectifier. The + & - DC legs will show about 44vDC (it gets a little bump from the switching of the AC I think.) Create a center leg by bridging a pair of equal 5w resistors between the two legs. Also bridge a pair of the big caps across the DC legs. Then connect a wire from the center of the pair of resistors to the center of the caps. This is now your zero v leg and is exactly half the distance between the original legs. You also want to use two ground posts for the whole system that I think this instructable showed if I remember correctly. One ground post will be your zero v power leg, and any ground references in the power circuit will ground to this. (Like the resistors or caps that connect positive and negative voltage to ground in the diagrams.) The other ground post is for your audio ground references. The input in the diagram usually shows only the positive audio input, but it is assuming that you know to ground the negative side. Some schematics show to route the negative through a resistor or a cap. Also, the inverting input of the chip (the minus audio input symbol on the chip itself) has to be referenced to ground with a resistor. This is to set the gain by comparing the ground reference to the feedback resistor between the output and the inverting input, and it also goes to the audio ground. Finally, the final output negative side comes from the audio ground while the positive terminal is the audio output of the chip, which somnetimes goes through a resistor or small cap itself. I had to stare at the schematics and project photos for weeks before I got it and could hook up an OP Amp without making smoke. I highly recomend getting a breadboard and a couple of TL082 OP Amp chips from Radio Shack. The back of the package for the TL082 shows which additional components you will need to hook it up. Pay special attention to the wattage of the resistors and the voltage of the capacitors. I have popped caps right in my face before, and they go off like an M-80. The caps need to exceed the voltage between your zero and plus or minus legs, as that is what will be surging through them. You adjust the gain you want by the ratio between the feedback and ground reference resistors on the inverting input. One you get it all working on a breadboard with a $1 TL082, you can try with a 7 or 8 dollar LM3875 or 4780. On the breadboard, you can use four 9v batteries in series to get +/- 18v. The TL and the LM's I think need at least 12 or 15 volts +/-. Even +/- 18 volts will make smoke if you short something between the + and - terminals (36v total). Welders only run at about 48v so be warned. You can easily feel 24 volts and up through your skin too. One last warning too. If a chip has a hole to screw it to a heat sink, screw it to a heat sink. The TL082 does not, but it only draws like 2 watts. An LM3886 draws 68W per channel, and will cook off in a couple of seconds at full power. If the back of the chip is bare aluminum, you should have insulating silicon between that and the heatsink if the heat sink can touch ground, or it will pop. The LM3886 is the plastic encased version of the 68w LM, and can be attached directly. Hope this all helps. Just message back if you have questions. I have some other helpful links I can send when I am booted into linux instead of Windoze. Cheers, Scot

    Wow, how long did it take you to type all that? :D Thanks a lot actually, I think i get the basic jist of it. Most of the stuff that I've done with electronics so far has been digital on a five volt level, so I really didn't know anything about the negative voltage part of electronics. You learn something new everyday!

    Yeah, I agree with that! Digital is cool though. But I agree. Once you get your head around negative voltage, its easy. I just thought I'd let you know, I built another amp, and am posting pics tonight.

    Thanks for answering that. I was getting around too it, but was working out how to explain it. Oh, just thought I'd say, I blew up the amp the other day. I don't know what happened. I think something shorted out. BOTH of the caps on the back blew their tops out, smoked my power supply, and melted a few resistors. I'l build another amp very soon, I miss my music. And I GUARANTEE I will document this for all of you guys!

    I know what you mean. My amp is a pair of little board kits I got on Ebay for $25 stuck in an old Mitsubishi surround chassis that has a really clean sounding transformer. I doubt it sounds quite as good as a direct-wired chip amp, but the sound of these things is addictive! I can't quit listening to the acoustic version of Hotel California on it. It just continues to blow me away how great it sounds. I have more than a dozen receivers from the 70's, and this one runs circles around it. I really hope to get a direct-wired amp like yours working someday soon.

    Sounds awesome. Post some pics of the internals, I'd love to see.

    Well, I didn't really know about the 'direct wired' amps until recently, and I can tell you, this amp wasn't originally built like that.

    I got a free amp chip, had a rummage through my junk box, and realised I had all the parts. It wasn't built as my main amp, it was just a sort of experiment to see how small and epic-looking I could get it.

    Based on the comments, I think it came out alright. The best amplifier, which is also my main amp, is a 20W stereo amp I built from a kit, but have modified it to an amazing extent. I might post a slide show of that too.

    Basically, I have added a pre-amp to its internals, put large and cleaner caps in the power supply, changed the heatsink from one of these to a massive, fan forced heatsink I got off an old pentium processor. Added another bridge rectifier for a 12V rail, tapped of the transformer, added gold plated input sockets, but the best thing is, I've had this amp for over 5 years now and it gets daily, loud use. Also it has been hooked up to just about every speaker under the sun, some faulty and it has never blown an output chip. Hmm, I think I will post a slideshow today.

    Anyway, thanks everyone for the comments.

    Thanks. Might have to hunt down some of those chips!!!


    Wow, it looks like you're running the risk of a lot of short-circuiting on that thing.

    is this for real. how can it be an instructable without the instructions on how to build it. You should make it a video instructables instead if your tired of writng down the procedures, not just this slideshow

    1 reply

    It's not an instructable. It's a slideshow. Get your facts straight. A slideshow isn't meant to have instructions, and nobody said anything about a video.