Introduction: HI-FI LM386 Stereo Amplifier
I have seen a lot of LM386 amp designs that have all been "easy to make," "use few parts," or just "small," but most of these amps just don't sound that great. I wanted to build an LM386 amp that actually sounds good, no matter how many parts it may take. So with a LOT of trial and error and research, i came up with this design which produces a very clean sound with no distortion, clipping, or other noises that typically give the LM386 amp a bad name!
Step 1: Gather Parts and Build!
Since i wanted a stereo amp and the LM386 is mono, i build two identical circuits on the same board, only sharing the first two decoupling capacitors (C1 and 2). For the ease of reading the provided schematic, only one of the two channels is shown.
The parts required are:
- PC board (i used strip board)
- LM386 IC (x2)
- dip-8 IC socket (x2) (optional but suggested)
- speaker (x2) (4 to 8 ohms each, at least 1 watt)
- female spade terminals to connect speaker wires to speaker (optional but suggested)
- stereo audio jack
- 100pf, 33pf (x2), 33nf (x2), 47nf (x2) non-electrolytic
- 100uf, .22uf (x2), 10uf (x2), 220 to 1000uf electrolytic (x2) (the .22uf could be non-electrolytic...your choice, both work well)
- 10r (x4), 22k (x4) 10k (x2)
- a power supply of your choosing-- 4v to 12v. I used the guts of a 12v 100mA wall wart
- on/off switch ( I placed the switch before the power supply on the mains voltage so the power supply would not be drawing power when turned off)
- hook up wire: 22ga for low voltage connections, 16ga for high voltage (If needed)
- speaker enclosure(s)
- led and 610r resistor for power indicator light (not shown on schematic and optional-may have to adjust resistor based on supply voltage)
A little explanation of what is going on in the circuit...
C1, 2, 4, and 6 provide decoupling. the LM386 needs a really clean, steady dc power supply, otherwise it will amplify ac noises from the power supply.
r1 and c3 form a low pass filter that prevents the highest frequencies from making it to the amp.
r2 and r3 form a preset voltage divider for volume control. Anything i plan on plugging into this has its own volume control built in, so a potentiometer, for me, was not only redundant, but another cause of noise. Also, if the input signal is amplified too much, the amp will be over driven and start to clip. This is also why i did not put a capacitor between pins 1 and 8, which provides more gain.
c5 and r4 provide a bass boost for a deeper sound.
r5 and c7 form a zobel network to prevent high frequency oscillations at the speaker.
c8 allows the ac signal to flow to the speaker, while preventing dc from shorting it out. The larger the capacitor, the more bass signal can pass. I only used a 220uf, but you can use up to a 1000uf.
Step 2: Design and Build a Speaker Enclosure
A large part of the great sound is not only the elaborate circuit, but a sealed solid enclosure for the speakers; leaving the speakers in free air will diminish the sound quality. When I first started this project, I used some speakers that I salvaged from a dead flat screen TV that my neighbor gave me. They came in their own enclosure and sounded great... but looked funky. Ultimately, I wanted something that was a little more aesthetic so I found another pair of decent speakers that were 3" in diameter, had big magnets, and a flanges so i could bolt them in place. I tested them by placing them in soup cans and sealing the edge with electrical tape. They work quite well.
For a permanent enclosure, I built a box from 1/4" plywood (aka luan or underlayment), 3/4" x 3/4" lumber and plexiglass that is 5" tall by 5" deep by 12" wide. The top and back of the box are plexiglass, so the internal components can be viewed. I'm not the greatest carpenter, so I'm not going to go through all of the specifics, and you can use your imagination. The most important things are to use solid material (avoid thin plastic and metal) and no holes in the enclosure for air to move through (caulking if your friend!)
I did have problems working with the plexiglass. It took four tries to get the rear panel because of cracking. If you choose to work with plexiglass, don't rush or try to force something through a hole that is just too small! Make the hole a little bit too big and seal it with caulk!
After I built the enclosure, I test fit the electronics to determine wire length needed for the power supply, switch, and speakers. I soldered most of the power connections and added female spade connectors to the speaker wires for easy installation. Then I disassembled it, and finished the box with stain and polyurethane for a nice look and some protection.
Step 3: Put It All Together
For final assembly, I glued the power supply in place because there was no room on the board to drill for a mounting hole. Then I put the power cord in a strain relief bushing and snapped it in place in a hole in the plexiglass. I made the final terminations from the power cord to the power supply with crimp connectors before mounting the plexiglass. Instead of caulking, I used some foam gasket to seal around the lip of the plexiglass, just in case if I ever have to open the box back up. I screwed the plexiglass panels down with 10 round head screws each, and alas the top plexiglass panel cracked on the last screw because i over torqued it! The crack is small and mostly unnoticeable so i left it...
I plugged the power cord in to the wall and the audio cable to my cell phone, flicked the power switch on and it started playing right away and sounds great!
I hope this Instructable helps someone out with design ideas for a LM386 amp build!
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