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DIY HiFi Gainclone Power Amplifier (2x68w, Class AB-A, LM3886)

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I've made gainclone amplifier that uses a LM3886 chip. It's one of the best compact HiFi amplifiers. It is a Class AB-A (conjugate)  amplifier that has a fully symmetrical structure (push-pull), this mean that the sine waves  produced, will produce a + , - output. A 25 volt (+/- Dual Rail), 5 Ampere, toroidal transformer was used to supply electricity for the amp. There's also a PCB Layout provided for the project. I found an old CPU processor attached to a gorgeous heatsink & fan, I recycled both of them and drilled holes for it to be mounted on the LM3886 chips. 

Specifications:
- Maximum Output Power: 68W RMS - 108W Peak
- Frequency Response: 7Hz-25kHz (Filtered ⇒Linkwitz)
- THD: %0.03 at 60W
- SNR: 110dB at 60 W - 92.5dB at 1W
- Output Class: AB-A (Conjugate)
- Auxiliary Features: DC/AC Short circuit protection and thermal protection.
Working Voltage/Power: 12-94 Volts (Dual Rail), 1-10 Amperes
- Audio Features: Input Mute Funtion (100% silent = no input)

Too bad I had a late documentation, that's why I only have a few pictures of the steps and procedures. Due to the late documentation, I had to get images from the original source. Some of the pictures are not mine, there are no claims that the PCB designs are mine nor the diagrams, although there where some modifications made by me for the amp.

What Is A Gainclone?
Back in 1999, relatively unknown manufacturer 47-Labs released the "Gaincard" to rave reviews. It immediately caused controversy because it was based around a $5 power amplifier IC (Integrated Circuit), yet a typical setup would cost you around $3300. A Gainclone in the other hand refers to any DIY amplifier that uses a LM3875/ LM3886 as it's main component. 

What's So Special About It?
The gainclone only uses small amounts of space, it's built with a minimal supply of components, yet giving a great HiFi result. It beats the hell out of those modern HiFi amps, it produces 2x68 watts of power, with a Total Harmonic Distortion of 0.03%THD and built on a 2x3 PCB board!  So why doesn't the audio industry use it? I'm not really sure. All of these sounds "too good to be true", I recommend this project for those who are still starting on their DIY HiFi amp hobby, since it only uses some few components.

What's A Power Amp?
A power amp is a amplifier with no preamp, volume control, tone control, or any auxiliary devices attached to it. It's just pure simplicity.

Coming Soon: DIY HiFi Preamp With Tone Control (Works With The Gainclone)

 
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dagob2 years ago
It is added to my favorites list. I always wished to build my own amplifier. I believe this is the time to do it. Thanks for all the info.
rimar20002 years ago
This is a very interesting project, thanks for sharing.

Where did you get the transformer? They are so expensive on amazon.

ASCAS (author)  rusty.shackelford133723 days ago

From a local repair shop. They sell scavenged transformers from unrepairable appliances.

Oh ok thanks, I'll check Murphy's surplus (local industrial/military electronic scrap), they have all kinds of stuff, capacitors, transformers, vacuum tubes (valves) you name it. Is it possible to use an Ei transformer? Also, should I use a 5a output fuse for the output stage in case of LM3886 failure?

ASCAS (author)  rusty.shackelford133723 days ago

Yes Ei transformers work fine just be sure it supplies enough current to the amp. Yes, I would also recommend using a fuse.

So I've got a small undocumented Plitron, 2x115v primary (I've paralleled for my country- 115v), 2x9vac out and 1x15vac out, toroidal.

ASCAS (author)  rusty.shackelford133715 days ago

You need a transformer higher than 2x9v (dual rail). You could buy two of these, use each as a single rail 1x15v and create a 2x15v dual rail out of it.

:))

yhdesai1 month ago

CAN I USE 12 PIN IC BASE FOR LM3886

ASCAS (author)  yhdesai23 days ago

What do you mean by 12 pin?

yhdesai ASCAS21 days ago

can i use this for lm3886

images (3).jpg
ASCAS (author)  yhdesai21 days ago

There's no need to use a socket, it would just melt from the heat of the LM3886.

yhdesai1 month ago

GREAT INSTRUCTABLE AS USUAL

frog812 months ago

Hi. I'm new to electronics and I have a question. For the split rail supply, is it possible to use the circuit below instead of using a centre tapped transformer, because I can't seem to find an appropriate one on the web. Obviously, the half wave rectification will mean an increase in filtering capacitance, but will 20000uf be enough? Plus, is the signal ground down the middle able to handle the combined current from both Vcc and Vee?

Thanks in advance.

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Inducktion4 months ago

I think you may be over-exaggerating on the price of resistors in America... Maybe if you buy them from Radioshack (but they mark up damn near everything they sell) but if you just buy them from China or eBay the price is a lot lower.

circusbrains5 months ago
Great instructable!
circusbrains5 months ago
I've never seen $1.00 for an American resistor!

kriksis5 months ago

Hi,
Call this a silly question but I see only one AMP (LM3886) in schematics. Is this like a schematics for a parts used to set up one AMP? And then the same schematics are repeated the same way for the second? If so, how are they connected?

Thank you in advance!

ASCAS (author)  kriksis5 months ago

Yes, the single LM3886 is repeated for the second channel.

:)

luismoro7 months ago

Hello, ASCAS
I want to build an 2x50W amplifier and I'm basing it on your design. I'm new at audio stuffs and i'm having some doubts about the concepts....
I'll build two bookshelf speakers from a JBL two-way kit (Mid-bass + tweetter + crossover) and I was reading the LM3886 datasheet for the amplifier project.

My main question is: the LM3886 supports two output speakers, so why did you used two chips instead of one? All other projects use two chips too.... that's better? So in this case, if you use an mp3 player as input, each channel goes at one amplifier and the ground is common?

If you have some material to indicate to me, i'll be thankful!

ASCAS (author)  luismoro7 months ago

Hi! It's nice to see that you're gaining interest in audio. Yes, it's true that a single chip of the LM3886 can support two channels. The reason why people use two chips instead of one is because they want to get twice the power (watts) of the output.

It's called amplifier bridging. Not all amplifiers are compatible to it. Luckily the LM3886 does. This is done by merging two input:output channels of one chip, in other words, you're assigning a single channel for each chip :)

luismoro ASCAS7 months ago
Thank you so much for the answers!
Actually, I realized that I need an 2x100W amplifier, because both speaker and tweeter has a power of 50W each, thus the total power per channel would be 100W.
My speaker/tweetter has an impedance of 4 ohms. Since the LM3886 delivers 50W into 8 ohms at Vcc=+/-35V, if I connect speaker+tweetter in series, I'll have a total impedance of 8 ohms. So I'll need 2xLM3886 to deliver 100W into 8 ohms, but when I bridge the LM3886, the output impedance changes?

If the output impedance is cut in half and my logic is correct, I can brigde 2xLM3886 to deliver 100W into 2 ohms at Vcc=+/-28V and connect my speakers in parallel to achieve 2 ohms output load. Is that right?

I can't connect a 8 ohms load into a 4 ohms output, but I can do the oposite, right?

Luis, you are not correct. If you have a typical speaker which has a 50W woofer, and a 50W tweeter, plus a passive crossover (to send the low frequencies to the woofer and the high frequencies to the tweeter) then the proper amp to use would be about 60 to 75 watts. You can use a 100 watt or 25 watt or even 2 watt amp, but the trouble is, that if you use an underpowered amp, you get massive distortion if you try to run it full blast, or if you use an overpowered amp, and you run it full blast you will overpower the speakers. Two things that kill speakers are excessive distortion (DC clipping) or excessive power (Burnt voice coil). So you want an amp that is about 10% or 15% larger than what your speakers can handle so you can run it at a comfortable volume without the amp being maxxed out. So 68 watts amps for a 50 watt speaker seems about right. Just trust your ears when you are setting the volume, if it sounds bad or distorted, turn it down or your speakers will be nothing but doorstops in a few minutes.
As for ohms, two 8 ohm speakers connected in parallel make 4 ohms, two 8 ohm speakers connected in series make 16 oms. So you can wire up your speakers to suit whatever your amp can handle. A high quality amp can handle 2, 4, 8, or 16 ohms. The power decreases as the ohms go up, so keep that in mind. For this amp, I haven't looked at the spec sheet, but to be safe I wouldn't run it below four ohms. Heat increases as ohms go down so you wouldn't want to melt the amp by running it too hard.

Hope this helps.

I was reading the application report for the LM3886 and I can drive loads lower than 4 ohms using parallel configuration. In parallel (Quote: "For example, using four ICs to drive a 1Ω load means that each IC dissipates 1/4 of the total power dissipation. In other words, the load to each IC looks like a 4Ω load"). Look at the picture to see how I should wire my speakers (I intend to use a two-way kit). Since loads are setup in parallel, I need an outpute voltage of 14,14Vrms to obtain 50W at each 4ohm load, right? Using 2xLM3886 I can get this voltage, but I divide the total current for each CI. This way the amp run softer. Please, correct me if I said anything stupid =)

I don't understand why you've said to add 10 to 15% power to the amp. This will not burn my speakers? Or I do this, but I limit my input, so the output voltage never exceeds 14,14Vrms for 50W?

I read a lot since last question 15 days ago and I'm beginning to understand how to design the amp, but DIYs and people answering my questions has been REALLY helpful! Thanks a LOT!

Diagrama de ligação do divisor de frequência com woofer e tweeter.jpg

Music power is not constant, it is always fluctuating. So what we are talking about is the long term average, or RMS wattages. There is a lot of flexibility built into the RMS figures. So don't think of the power rating of a speaker as a hard and fast figure you can never exceed. The speaker will probably handle four times as much power for a brief second, it's the long term average that needs to stay close to the speakers power rating. You could drive a 50W speaker with a 1000w amp, as long as you kept the volume low. Like I said above, don't let the amp distort, and don't let it run at much higher power than the speaker can handle for a long period of time, and you will be fine. Let your ears be your guide.

achand86 months ago

So you need 2xLM3886 for stereo output?

ASCAS (author)  achand86 months ago

Yes.

The project has a bridged structure. A single LM3886 is capable of driving two separate channels, but for this project we bridged the two channels on each chip and assigned each chip for separate channels. This is done two double the amplifier's power output.

achand8 ASCAS6 months ago

I only see one output and one V+ and V- in the pinout shown, so hows that two channels ? A single channel can provide 68W?

dark2knife8 months ago

Hello, few years ago I tried to build 300w amp but I couldn't make it work due to bad parts, schematic or my own fault. Since most expensive parts are working (PS), I would like to build this specific amp. Only problem is high voltage of +-60V. What effect do you think it would have on this amp? Would it just gain more power (how much more?) or overheat and malfunction? I still don't have speakers for it. Thanks.

andrew_h9 months ago

Just wanted to drop a message to say thanks so much for this instructable. Ever since i saw it on the featured email I wanted to build one (not even knowing they existed previously) and started collecting parts almost immediately. I now have a complete dual mono gainclone assembled but still in development on my bench and i love it. The reason it's still in development is that like you, I am putting a sound processor and source switcher (using a TDA7439, 16X2 LCD, DAC, rotary encoder and an arduino to control it all) in front of it and its almost complete. Thanks so much for the inspiration! And to anyone else - If you make one of these you will want to bin any other amp you own. The sound quality from these is AMAZING!

ASCAS (author)  andrew_h9 months ago

Awesome! I'm glad you like it!

___________________________

What a coincidence! I was finishing my Arduino Gainclone Amp when I received a notification from your comment :)) I was supposed to post the guide today but I'm struggling to find a "digital volume control module". The remote + LCD display would be a waste if I didn't add a digital volume control.

andrew_h ASCAS9 months ago
the TDA7439 is your answer. it does 4 input switching, bass/mid/treb gain, balance and volume. you really cant go wrong with it. tje downside is that it uses a dip30 package so hard to proto. i have also written a (so far unreleased) arduino library to control it. I have only just got mine on to a board today so up until now it was mostly theory but it works great.
jimbuntu11 months ago
Thank you! this will be my next project!
tazbodel1 year ago
Hello! I have a question for you:
Do i really need a preaamp ? i really want to build this project of yours.
Keep up the good work
ASCAS (author)  tazbodel1 year ago
Well the preamp is optional. If you want to enhance your bass and treble then you'l need it, but if your a purist you can connect your audio device directly to the gainclone amp.

I'll post the preamp tutorial around October.
tazbodel ASCAS1 year ago
Thank you so much. I hope the amp will be finished till the end of octomber (i don't really have to much free time) and then maiby i''ll do the preamp to.
Minisoft1 year ago
Do you have the eaglecad file.. if so could you send them to me.. pc_geeks@msn.com thank you
Thanks for sharing. However, I think you should mention the original source (which is located at http://bit.ly/TR6Wv7 ) since you used some PCB shots, schematics & PCB and that site mentions CC BY-NC-SA license. Keep up the good work!
I think this is the best project you have ever built! It is amazing how you built that from scratch and made it look so professional. Keep up the good work!
ASCAS (author)  project_builder2 years ago
Thanks!

But this is not my best project. I have tons of them. I haven't documented most of them. I have a new amplifier, built in an aluminum chassis, and has a intricate PCB artwork and schematic. I hope to release an ible' about it soon
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