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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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dagob1 year 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.
rimar20001 year ago
This is a very interesting project, thanks for sharing.
frog8127 days 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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Inducktion2 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.

circusbrains3 months ago
Great instructable!
circusbrains3 months ago
I've never seen $1.00 for an American resistor!

kriksis3 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)  kriksis3 months ago

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

:)

luismoro5 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)  luismoro5 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 ASCAS5 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.

achand84 months ago

So you need 2xLM3886 for stereo output?

ASCAS (author)  achand84 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 ASCAS4 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?

dark2knife7 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_h7 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_h7 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 ASCAS7 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.
jimbuntu9 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_builder1 year 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
Quote:
... 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.

Actually, the National Semiconductor Overture-series ICs are widely used in professional recording equipment. My own "hi-fi" is based around multiple active near-field monitors that each have a pair of the LM3886 chips.
Hi PurplePeople, nice to know some one on instructables.com is on HiFi!!! (I've been critiziced because some other instructables people are simply looking for low fidelity articles).
But I'm puzzled by your statement that says that your HiFi is based on "MULTIPLE" near-field monitors... What exactly do you mena by "multiple"?

My HiFi is based on a pair (Left and Right) small speakers (modified old Miller&Kreisel Satellites) and a single subwoofer; but to be multiamped and connected to several small power amps, such as this "Gainclone".

It is my belief that passive crossovers degrade the sound too much, are a pain in the rear to adjust and never will drive the speaker as well as a direct connection to the output stage. Just a look to the horrible impedance curve of most passive crossovers gives a clue to the nightmare that those present to the amplifier... I've measured some impedance curves from expensive speakers going to low values of around 2.1 ohms, and then rising to over 30 ohms at certain frequencies!
My active is based on Linkwitz-Riley 24 dB/oct, 4th order crossover. By the way, very few people is aware of the beautiful stereo image that a couple of properly set-up near field monitor achieve. Amclaussen, Mexico City.
ASCAS (author)  amclaussen1 year ago
It's great to find people interested in HiFi setups here in instructables. I' planning to build a new pair of bookshelf speakers. What are the advantages of building a 4th order linkwitz crossover. Right now I'm using a 2nd order linkwitz crossover in my DIY Bookshelf Speakers (Next "Ible"). My dad has a complete setup of B&W speakers (Towers, Bookshelves, Monitors)  Cambridge Audio Amp, DAC magic upscaler, iPod DAC, a Monster sized THX certified Onkyo Receiver and more. 

I'm actually planning to beat his setup with my cheap DIY HiFi setup. Right now I'm planning to build a pair of bookshelf speakers similar to the Polk LSiM setup. What kind of crossover would you recommend (structure/ type) I'm going to build my next one from scratch (coil winding). This is my current pair of DIY Bookshelf Speakers.

I'm also planning to build a MJ15015 & MJ15016 transistor amplifier, this time it's better than the gainclone and has a more intricate PCB structure.
Hi ASCAS, Nice project, I will vote for it. To really understand the MANY benefits of Active Crossovers and multiple amplifiers connected directly to the drivers, I will suggest you to visit: http://www.sound.westhost.com/bi-amp.htm
The gentleman(Mr. Rod Elliot) that wrote that two part article IS a very intelligent, top-notch engineer and a very clever person. Read carefully the two parts of the article before starting buying components. 4th Order crossovers of the Linkwitz-Riley alignement are generally (but not universally) regarded as a very good design. Crossovers produce certain undesirable effects, like Phase shifts and summing errors (remember we are trying to reproduce a perfect sound wave in the space in front of the ears of a critical listener, but when trying to divide and sum again the frequencies, amplitudes and Phase of the signals sent to the two or more drivers, it is a very difficult task to achieve a flat response that sums properly without lobbing or interference effects, both above and below the listener height, that the room walls will reflect and interfere with the direct sound, thus producing undesirable effects. Nevertheless, you could certainly give your father system "a run for their money" with a much less expensive system IF you keep an eye on the critical aspects. I will suggest to go to a full multiamplified DIY system. When an amplifier has to handle only a very narrow band of frequencies, it has a much less difficult task to perform, therefore you can use realtively small amplifiers to drive every crossover band, instead of having a large, very expensive amplifier meet the duffcult task of reproducing all of the frequencies perfectly at the same time.  Why is that very few speakers come properly multi-amplified, and almost ALL of the High-End business is based on a combination of VERY large, tremendously expensive amplifiers that waste a lot of power in a tremendously complex and imperfect passive crossover inside a large speaker? (Hint: it is a matter of price and economics, not sensible engineering at all. The discovery of active crossovers would cease the sale of those majestic, heavyweight, overly inefficient amplifiers costing many thousands of dollars. that is why it is usually used on professional setups, where there are NO amplifiers capable of delivering thousands of clean watts to professional speakers in live concerts on large auditorioums. But on the home environment, the large, heavy and very expensive "magical" amplifier is a much better business for the manufacturer and the esoterical salesman. Both make much more money selling such amplifiers, speakers and esoterical, magical cables costing a thousand dollars a foot!
BTW, Rod Elliot sells PCB's for his crossovers and many other pieces of equipment.  Unfortunately, he lives in Australia, so delivery times are not as short, but his designs are impeccable!

If you understand the merits of multiamplification, you will soon find that the large amplifier you are dreaming, using large TO3 discrete transistors is possibly ONLY NECESSARY for the woofer, and that the design of that amp will not need to be as good, since it will handle the lower frequencies only. Plus, you will save a lot because the huge crossover coils required for the woofer, will be replaced by small, precise capacitor-resistor combinationsinside the Active Crossover.
My two cents.  Amclaussen.
P.D.: Beware of the existence of FAKE large transistors in the market... Take a look at Rod's site on FAKE components.  This is big problem for us, the builders of large amplifiers. I've seen that same transitors you plan to use falsified by using a much weak 2N3055 transistor chip inside fake bodies.  As soon as you power your creation, those fakes will burn immediately in a puff of smoke.  Truly original large TO3 transistors are expensive and scarce, be sure the one you buy are the genuine ones! (Really! there are quite a few Chinese factories faking a lot of components... they take a cheap transistor chip, and re-package it inside a larger case properly (but falsely) marked to pass as the genuine one. You can hardly identify those, they will test OK with a multimeter ot transistor tester, but will fail misarably when subjected to the large currnts and voltages they are supposedly capavbe of handling.  This is a REAL problem.
ASCAS (author)  amclaussen1 year ago
Thanks for the quick response, I guess I still have a lot of things to learn about amplifiers and speakers. 

Don't worry about my TO3 transistors, they are 100% original. I bought Them in DEECO and Alexan, those stores are as reliable as radioshack, its actually better than radioshack because they almost have everything and everything is much cheaper, things are so cheap that I even have an abundant supply of parts at home. They work fine,  I'm also finished with the "MJ" amp, it sounds great, all it needs is a preamp with a tone control. Have you tried the TL072. Right now I'm using a TDA1524 tone control, it's not much of a HiFi though. 
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Since 2003, my living room has had a pair of Yorkville YSM1P active studio monitors beside the TV and a pair of Tannoy Proto-J for surround. The Tannoys are amp'ed with an "old" Marantz 1530 and they are all fed by a Sony DVP-NC650V SACD multi-changer that is run through an "old" Teac 2A mixer. No sub since the YSMs really can do 40Hz. But, if I ever get around to it, I'll build a transmission line sub for an old Sansui amp that's been waiting for a chance to join the chorus.
ASCAS (author)  PurplePeople1 year ago
Oh yeah. Although I was comparing it to our audio setup, a Cambridge Audio 550 Azur, and also those NAD amplifiers in the market. My dad has always been into pro-audio, I've been exposed to a lot of audiophile setups, in different show rooms. He also owns a complete set of B&W speakers (Bowers & Wilkins) that.

It made me wonder, why did all those audiophile amplifiers use transistors or mosfets instead of IC chips.
All those discrete components help make the amplifiers heavy enough to qualify as "audiophile". The nice thing about recent hi-fi is that pro-audio has finally penetrated the audiophile clique.... witness Bryston, PMC, etc, and Sennheiser, AKG with headphones.
EXACTLY!!
There is a lot of money to be made by making the "audiophool" believe the amplifier has to have 40 or more large TO3 metal cased transistors, a two kilowatt toroidal transformer weighting more than 30 pounds, several square feet of aluminum heat sink ribs and a huge chassis. Those Audiophools are quite happy expending a LOT of money in a truly maginificent work-of-art. But if you are capable of a little DIY magic, you can assemble a much less expensive (about 15% the cost of the large amp alone) system by buying or assembling the much less powerful amps required to properly handling a directly driven speaker component by using active crossovers. Even clean AUTO amplifiers (I have succesfully assembled some damn good systems by using inexpensive, IC output Alpine brand 20 watt, 12 V amplifiers directly coupled to the midranges and dome tweeters. Only the bass amp needs to be more powerful, but mot much, around 100 W for a normal size listening room to sane and healthful levels! Amclaussen.
The probable explanation is that in the first years of IC's, they had a lesser sound quality, mainly because of the difficulty in making the capacitors inside the IC good enough for quality audio. IC Op-amps have advanced enormously since the days of the first ones. Those of old age were the truly ugly sounding "741's". Years later, some companies pursued much better IC designs, like Signetics, and Burr-Brown. In those years, a popular modification was to simpy replace the IC's with better (usually faster, wider bandwidht) IC Op-amps. Some times, the replacement was counterproductive because a faster IC could oscillate badly at ultrasonic frequencies. But with luck, a nice difference coud be clearly heard sometimes. For these reasons, IC's got an undeserved bad fame when compared to discrete circuitry, that could use much larger and "better sounding" capacitors. But the potential is there: a properly designed ands built IC can certainly sound undistinguishable from a discrete circuit. And in large, very powerful amplifiers, it is not possible to get large enough power levels and specially. large current levels possible with discrete transistors. Additionally, those really large, impressive build, ultra heavy High-End amplifiers that cost many thousands of dollars, are like a work of art. But the question is: is REALLY such an amp needed to produce a good result? In my viewpoint, you only need about 100 W continuous (incorrectly referred as "RMS") at 8 ohms for a Bass channel, and about half that amount in an active crossover system for the mids and possibly another 20 clean watts for the highs. Remember the heavy full range amplifier wil WASTE half its powert in the damn passive crossover! (resistance of the large woofer crosover coils, Zobel networks and level matching resistors). Amclaussen.
amclaussen1 year ago
Just a few suggestions from my experience:

1) Coaxial wire: Years ago, I was building an old (but excellent) preamplifier from a kit by David Hafler... I thought "why not replace the cheap looking twister pair wires from the RCA inputs to the PC board with a "much higher shielding" coaxial wire? I did, but found with dismay that the Preamp worked BETTER with the humble twisted pair! Later I learned that a simple looking twisted pair has even lower capacitance and a better behaviour than the best shielded coaxial wire, and that the late Mr. David Hafler had it right from the beggining!

2) Fan installation: As shown, the lower half of the enclosure blocks the flow of air to the fan inlet... I humbly sugest to open up a series of channels made with a Dremel tool; or multiple round 1/4" holes to be drilled on the emclosure.

3) Enclosure: While a plastic enclosure is shown, and possibly works OK, I would prefer an aluminum or steel one. The inexpensive but helpful 18" metal bending brake from "Harbor Freight Tools" does a good job when making metal project boxes from either steel sheetmetal or aluminum. Another possibility when making compact electronics, is to use a piece of heavy wall aluminum profile rectangular tube. I've used some 4" x 2" aluminum rectangular profile to make excellently shielded chassisses. Amclaussen.
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