Wednesday, March 5, 2014

50W Power Amplifier with LM3886

This is my second encounter with LM3886. I was pleased of the sound this chip produced the first time, so I decided to make another amplifier with it.


The schematic is based on the schematic in the datasheet  of the chip with minor changes.


I removed the time delay capacitor connected to MUTE pin, because it's better to use separate DC protection schematic which has similar functionality.
I made the output  inductance L1 by winding 15 turns of enameled wire around  the resistor R7. The diameter of the wire must be minimum 0.4mm. The whole was wrapped with heat shrink.
I used 47uF/63V non polarized capacitor for C2. It can be regular electrolytic capacitor, but it's better to use non-polarized or bipolar.

Here's what the finished boards look like:





And here's my test setup :)

The transformer is 2x24VAC / 105W. The test was ran with 8Ohm dummy load and the big heat sink gets only warm after hours of playing music from my computer at max volume. The transformer is a little weak for this amplifier, maybe 150W or 200W would be a better choice.
The power supply is very simple - a bridge rectifier and 4 x 10 000uF/50V capacitors.

If the input is disconnected and open there is a little hum which can be heard only with an ear pressed against the speaker. But once the amplifier is connected via cable to the source and there is no signal, it becomes absolutely silent.
Also if the heat sink is isolated from the metal tabs of the chips with some mica pads then the heat sink is good to be connected to the ground to prevent inducing hum in the open inputs.
It can be mounted without isolation pads for better thermal conductance, but then the heat sink itself must be isolated from the metal enclosure which usually is connected to the ground.

How does it sound? Excellent :)


Update:  July 22, 2015

Now, after more than a year, I finished the amplifier :)
It's intended to be connected to my computer and will power two bookshelf speakers on my desk. The enclosure isn't the prettiest, but it is only 5 euro, so...
The heat sink here is much smaller than before and that's why there is a 60mm fan mounted on the back. It is powered by voltage regulator 7809 and it is inaudible. There is small empty space at upper left corner where I can put an EMI filter some time in the future :)

This is how it looks:






Link for downloading files of the project in PDF format: LINK
Use them on your own responsibility.
The PCB in the archive is a little different from that in the pictures - I changed the way R7/L1 combo is mounted. It's horizontal now which is more convenient.

Update December 3, 2015
One of my readers ask me for the PCB of the power supply. I haven't published it before, because it's very simple design and I think everybody should be able to make it himself . Anyway, here is the link for downloading the files for power supply: LINK
This is the schematic:
This is simple bridge rectifier with smoothing capacitors and bleeding resistors and connectors. There are connectors for DC input in case the bridge rectifier is not mounted on the board, but elsewhere.


11 comments:

  1. I found LM3886TF in my local market. Can i use this ic with your above design?

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  2. Yes, you can use. LM3886TF - "Isolated Package".

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  3. Yes man, you saved my day with your download link. My congrats and thanks from Brazil.

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  4. Guys, whats the voltage on capacitors. I see C7 is 63v but the others, please help

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    Replies
    1. All capacitors must have 50V or higher voltage rating.

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    2. Thank you very much.

      One more question, any alternative power source capacitor setup, i do not have 10,000uF, i have 4,700uF

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    3. It will work with 4700uf, but you will get strong ripples when you draw higher current.

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    4. Thank you very much for your guide

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  5. Strange experienced.. Everyone kept telling me not to go over 84 volt or else the chip would die. I have many of these little LM3886T, so I took the risk in testing one of them. I have a power supply that can produce +-36ct or +-48ct at 4amp. I am using the same size heatsink as in the picture without the fan. I first tested with +-36 parallel of 6 speakers, probably some loss through the wires but this brought it down to 2ohm. It sounds great playing "AC/DC Who made Who". Pretty loud with lots of punch. The heatsink was warm but nothing hot. I then switched it to the +-48, this is 96v total exceeded 12v, thinking it will die or not produce any sound because of the SPIKE. Well, it played the same "Who made Who" louder with stronger punches. I left it playing for days, thinking it could only max out for a short amount of time. It didn't give up. The heatsink was hot, but wasn't melting crayon hot. I measured the voltage at the chip's pins, taking in 96volt. when I turned it up full power, the voltage dropped a bit, but it was still 94volt. Has anyone tried higher volts?

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  6. Ooops... The links are dead, too bad!
    can you repost good links?
    Your blog is very good!
    Regards;
    Alain, from Marseille, France

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