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

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

Hi I'm Angelo! I am a college student taking my engineering majors in BS-EE/ BS-ECE at the DLSU. ...

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)

Step 1: Parts, Materials, & Tools

I can tell that parts in the US are highly expensive. Here in the Philippines a typical resistor would cost 0.25 centavos ($0.0006), while in america, a typical resistor would cost $1 each. There's a large difference. Also, parts are available here almost everywhere. That's the beauty of living here when you have a hobby of electronics. My project cost me P870.00 ($21.75) all in all.

Parts:
_______________________________________________

Others:
- LM3886 amplifier chip (2pcs.)
- 25 Volt, Dual Rail Transformer (Toroidal/ IE)
- Rectifier Diodes 6 Amperes (4pcs.) 
- 2x3 PCB board (2pcs.)
- Large Heatsink (2pcs.)
- Cooling Fan (1pc.)
- Plastic/ Metal Enclosure(1pc.)
- Binding Posts
- Female RCA Plugs
- AC Cable
_______________________________________________
Resistors:
- 20k 1/4 watt Resistor (4pcs.)
- 10k 1/4 watt Resistor (2pcs.)
- 15k 1/4 watt Resistor (2pcs.)
- 1k 1/4 watt Resistor (4pcs.)
- 2.2k 1/4 watt Resistor (2pcs.) 
_______________________________________________
Capacitors:
- 10,000uF 25v Electrolytic (2pcs.)
- 10uF 25v Electrolytic (4pcs.)
- 2.2uF 25v Electrolytic (2pcs.)
- 470nF Mylar/ Ceramic (2pcs.)
- 150nF Mylar/ Ceramic (2pcs.)
- 100nF Mylar/ Ceramic (2pcs.)
_______________________________________________

Step 2: Getting to Know Your LM3886 (I.C./Chip)

The LM3886 is the brother of the LM3875. It's the improved version. It produces a higher output wattage, and thermal and mute features are added too.

There are two types of LM3886 IC. One of them is unisolated LM3886T and the other one is isolated LM3886TF. Be careful not to mess with the isolation. The LM3886T requires a smaller heatsink, it's plate is conductive, a negative current flows through it, two LM3886T chips cannot be mounted on a single heatink without using a mica insulator, nylon rings and other insulation devices. A LM3886TF on the other hand, can be mounted on a common heatsink without insulation devices

The LM3886 is a high-performance audio power amplifier capable of delivering 68W of continuous average power to a 4Ω load and 38W into 8Ω with 0.1% THD+N from 20Hz–20kHz. The performance of the LM3886, utilizing its Self Peak Instantaneous Temperature (°Ke) (SPiKe™) protection circuitry, puts it in a class above discrete and hybrid amplifiers by providing an inherently, dynamically protected Safe Operating Area (SOA). SPiKe protection means that these parts are completely safeguarded at the output against overvoltage, undervoltage, overloads, including shorts to the supplies, thermal runaway, and instantaneous temperature peaks. The LM3886 maintains an excellent signal-to-noise ratio of greater than 92dB with a typical low noise floor of 2.0μV. It exhibits extremely low THD+N values of 0.03% at the rated output into the rated load over the audio spectrum, and provides excellent linearity with an IMD (SMPTE) typical rating of 0.004%.

Features:
- 68W cont. avg. output power into 4Ω at VCC = ±28V
- 50W cont. avg. output power into 8Ω at VCC = ±35V
- 38W cont. avg. output power into 8Ω at VCC = ±28V

Step 3: The Schematic Diagrams (for Amp and Power Supply)

LM3886 Gainclone Schematics: (source: circuit-projects)

As you can see, negative feedback line is revised. In this way, about 7dB is gained at 30Hz-70Hz band, and reached about 34db at peak point at 30Hz.

When 26v DC supply is applied to the given design, with 4 ohm speaker load and 2Vp-p input signal it gives about 65W RMS power. For users who want to use 8 ohm, we recommend +/- 38V voltage supply. Of course less than this value may be applied too.
Supply circuit is shown below,  It is simple too. There are two KBU series (6A) bridge diodes and 2x10000 uF capacitors. As a general rule, 2200uF stabilization capacitor is used per ampere but we are used to use 4700uF per ampere.  In our circuit, 2 Amperes will be drawn per line and we use 10000uF capacitors. We recommend you to use 2x10000uF capacitors per each line if you will use the amplifier in party mode.


Dual Rail Power Supply PCB:

It's so simple that you don't need to use a custom PCB board, you can use a regular old universal PCB. All you need are four 6 ampere, 50 volts rectifier diodes and two large electrolytic capacitors for filtering (the larger the value the better/ cleaner/less buzzing), 4,700uF is enough to filter the line.

Since this is an audiophile setup, I've been using custom winded toroidal transformers. Toroidal transformers has a lesser magnetic flux leakage, this means less buzzing thus you can put the transformer close to the amplifier circuit without hearing any buzzing sound from the speakers/ output.

I've placed the capacitors inside the toroidal transformer's core to conserve space (shown in the picture).


Step 4: The PCB Layout (for LM3886 Amp)

Here's the PCB Layout of the amplifier. There's a PDF file provided below, the height and width is set, don't worry of resizing the image. If you wan't to double check the printed PCB layout, get a ruler and it should have a measurement of 2x3 inches or something close. 
There's a flaw in the PCB labeling (ex: there's no C15), I will replace the schematic diagram soon, but for now, please use the schematic diagram from step 3 as your reference, please analyze the parts carefully. It will work, it just a bit confusing.


If you don't know how to make a custom PCB, you can either use a universal PCB board (perfboard) or you can read my other instructable about making a DIY PCB. The guide is useful, it got featured last September 3, 2011. You can click for the guide below.

DIY Customized Circuit Board (PCB Making)


Step 5: Soldering the Parts (PCB Assembly)

As I said a while ago, there are some flaws in the part labeling. No worries, we're just luck that the values are correctly labeled  it's just that the schematic diagram, did not match the PCB layout component map. I managed to make it work. Just analyze the foil patterns and the connections found in the schematic diagram and you will do just fine! 


As you can see that there are small tantalum and metal film capacitors soldered below the PCB, the original author did this because he ran out of space on the non conductive part of the PCB. Don't worry those tiny capacitors found below aren't really that important it's only used for line filtering (less buzzing), it's connected to the positive and negative power lines. As much as possible, try to buy those capacitors with a tolerance of 1%, this is done to achieve a better balance between both channels.

Step 6: Mounting the Parts in the Plastic Enclosure

Transformer/ Power Supply:
Try to conserve space as much as possible. I've mounted my line filter capacitors inside my toroidal transformer's core. Since the transformer doesn't heat up that much and the enclosure is tightly occupied, I just hot glued it to the enclosure. I also added a bright blue LED inside to create a cool professional glowing effect in the amp.

Heatsink With Fan:
Since the voltage applied is 25 volts and the fan requires only 12 volts of electricity, I used a 7812 regulator chip. If your not framiliar with it, you can just Google it, it is extremely common and easy to construct. As you can see, I've bent the heatsink in a "Y" shape for the screws to fit and to be mounted with the LM3886 chips.

Binding Posts And RCA Plugs:
This step is only a matter common sense. Just drill holes for the binding posts and RCA jacks to fit snuggly and tightly on the rear panel. I used a thin shielded coaxial wire for the RCA inputs and some gauge #16 (99% oxygen free) speaker wires for the binding post output.

Amplifier Circuit:
I rotated the whole circuit upside-down to conserve space for some future regulators or modules. It's better to add spacers to occupy hollow spaces as a support for your circuit board. I stuck a used/ recycled spool and glued a foam on top of it, for it to cushion the amp circuit.

Step 7: You're Done! It's Finished!

You're Done! It's Finished! It only took 6 steps to finish a Gainclone. I assure you that his amp will give you astounding results. It gives off a very neutral audio response. All you need to do is to make a preamp and tone control circuit (next project).

I'm currently documenting the tone control/ preamp circuit project. Only this time it's fully documented, instructions would be more specific, there will be more details.

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

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    78 Discussions

    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.

    This is a very interesting project, thanks for sharing.

    You did not need an LM7812, a mere series resistor would have been fine. Also you could run the fan quite a bit lower than 12.0V to reduce noise, if you had it drawing in outside air through a hole in the chassis. The way it is now, just recirculating heated air, makes no sense unless you're just trying to wear out the components faster from overheating. You might say it runs cool but if that is the case then I know you are not cranking up the volume.

    I saw in your description of the project that a preamp was coming. I tried to look for it but could not find. can you point me in the right direction, please? -hjp

    I know it is been a long time since you uploaded this, but if you could respond that would be great.

    2x68 watts means 68 Watts go through each channel, that i understand, but what if i were to use it as a mono amplifier by letting both channels out through only one output? will that make the power 134W or still 68W? thanks

    Hello. When I want to use it on 8 ohm speakers, I should pick dual rail toroid with +/- 38 V right? Also, how much amperes will be drawn when I use 38 V toroid transformer? If I use higher voltage, I need to change capacitor type for those with higher voltage, but capacity remains unchanged, right? Also, every other components remains unchanged right? Like 1/4 watt resistors etc.

    hello. great project!! one question. what is the power rating of the 25v toroidal transformer

    regards

    Bro I M w8ing for u reply. Plz

    Hi bro plz give me full detail and PCB layout plz it's a request

    Thanks for the guide. I notice that there are 2 ICs (LM3886TF) in the pcb you have given. However In parts list you have mentioned 2x3 pcb in 2 qty. since only 2 Ics are required for 62 WPC sterio, i am bit confused here. It would be great if you can clarify on this

    does the transformer has to have a mid point? does it need to be 25V? and how do i know what current is enough?

    Please help me, i dont know where to mount the components.
    The schematic doesnt match the pcb layout.

    Thx

    How to add volume controller any idea ?
    I m using this amp from past 2 years I want to add volume controller I m puzzle to find out the right option help me out of you know about it . Thanks

    1 reply

    You can add a potentiometer at the input.

    Hi i have just made this amplifier and it sounds great apart from when there is heavy bass it distorts slightly in the bass but im only useing a 2x12v transformer would this be the problem

    Why do you need a pre-amp? Can't you just plug your input from your CD player, FM receiver, Ipod, or whatever directly into the gainclone? Thanks for this, I've been thinking about building one of these for awhile.

    3 replies

    The preamp enhances the audio input. There's also a tone control feature added to it.

    where is the updated schematic? please upload i cant seem to work this project. i might be missing something. thank you

    What author probably means is that a "preamp" would add those additional features, but it is not part of this instructable.

    Hi! When will you upload the Hi-Fi Preamp???