Instructables

Inspired, by gum!
The inspiration for this project was actually two-fold. First, I needed to make a simple, portable guitar amp that would work with an electric bass guitar as well as an acoustic six-string (with a pickup), and could be played through a speaker or headphones. I knew I had all the components needed for a basic "LM386" audio amplifier, but the second part of the inspiration didn't hit me until I was looking for an enclosure for the project. I had a few empty Eclipse gum "bottles" laying around, and upon quick inspection, I realized that the opening at the top was 2¼" (60mm) - exactly the size used by many standard PCs for the internal speaker. The goal from then on was simple - make the entire 1-chip amp fit into the container underneath the speaker, with the lid threaded on over the speaker to hold it in place.

Skills and tools required:
I'm assuming for this project that the builder has some basic electronics experience such as breadboarding simple circuits, wiring and soldering. Tools needed for the electronics assembly are the usual hand tools - wire cutters, needlenose pliers, a low-wattage soldering iron and some rosin-core solder. A helping-hands vise setup would be great if you have one. Not a lot of mechanical skill needed here, just some drilling and light finishing which we'll get to in Step 5. A power drill and a few smaller bits (up to about  ¼") will be needed, and if you've never used one before, a tapered reamer is the perfect tool for getting all the jacks and switches to fit perfectly through the sides of the plastic container.

The components required are included in Step 1. You may have a few of them lying around, but even if not the whole list could be purchased for under $10.



 
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GiV114 days ago

Hello, i found this post very nice but i was wondering, can you use it also for a Bass guitar? and if not what do i need to chance or can you help me with making one? I don't know alot about it but i can make things like it only not develop them.

Thank you ;D

mdgrover (author)  GiV17 days ago

Hello GIV1 - thanks for the note. This amp will actually work fine with an electric bass. My son used one of the first ones I built with his bass.

GiV1 mdgrover7 days ago

Hey, thats niceto hear. Now i'm going to start to build one for sure ;D. And how can i maybe improve the amp if i for example take a bigger speaker what do i need to change or how can i calculate or how did you find this out.

Thank you so much already ;D

GiV114 days ago

Hello, i found this post very nice but i was wondering, can you use it also for a Bass guitar? and if not what do i need to chance or can you help me with making one? I don't know alot about it but i can make things like it only not develop them.

Thank you ;D

robman6161 month ago

Hi thanks so much for the great indestructible i have built 2 of them now. However, though they both work fine the speaker always has extreame amounts of gain, there is no clear sound. Any advice?

mdgrover (author)  robman61620 days ago

Hi robman616 - sounds like you made the original version since you have a speaker. What are you using for the input (acoustic or electric guitar, mp3 player)?

Guysmiley861 month ago

Just to add a lil more info. I made this on two different pcb's and still the same thing. All connections are good and nothing is touching. I really would like to get some help with this.

mdgrover (author)  Guysmiley8620 days ago

Hey Guysmiley86 - that's great that you were able to get this working fine on a breadboard. It's possible one or more parts could have been damaged from heat in the soldering process, especially the LM386 chip. Did you use a heat sink or other tool to protect the IC from heat while soldering the pins? If you're really worried about overheating the chip you can solder an 8-pin socket into your PCB and then just pop the IC into the socket afterward.

The Prof1 month ago

I have just finished making three of these and none of them work. I have checked and double checked the circuits and they are correct. All I am getting is a buzzing sound out of the speaker/headphone. And then I get nothing. Is there an erratum for the circuit? I have promised to make these for some of my friends and I have been struggling for 3 days. Any help would point me in the right direction.

mdgrover (author)  The Prof20 days ago

Hello Prof - apologies for the late reply on this. Any luck yet? Did you breadboard the circuit first or did you solder it together?

Dazzstudio1 month ago

good stuff

Guysmiley861 month ago

I am having a problem with this as well it works fine on a breadboard but when soldered together it works then doesn't. I do get some sound but it echos. Can u help with this???

kegerator4 months ago

Thank you for this, I hooked it up and sounds great (Rev 2, headphones only). However I only have sound from the left channel, is that normal.

vdo37 months ago

Any ideas on how to make a tiny little amp I can put in my pocket? I
don't need speakers just a headphone jack, I had one of those mini vox
amps that plug into your guitar but they're in the way and the jack
snaps easily if you accidentaly hit it on something since it's just a
big piece of plastic attached to the corner of your guitar.

Amiel Garcia vdo34 months ago
You could discard the speaker and just install the earphone jack
đdenda6 months ago

Can you tell me what I need to change to make it into a 1W amp?

I know I need to change LM386N-1 to LM386N-4, but what about other stuff? Potentiometer for example?
Thanks in advance!

đdenda đdenda6 months ago

Oh yes, I also have 2 speakers rated at 3W 4 Ohm. If I wire those to in series, will I get 8 Ohms?

Bro the wattage of the circuit can only handle 1/2 watt speakers so it wont work. Hope I helped. :)
Amiel Garcia4 months ago
Thnx so much bro it worked so well!
jhardenberg6 months ago

I want to ask, if I can't find the op-amp LM386, can I use any other op-amp? If so, what op-amp will works? Thanks before :)

mdgrover (author)  jhardenberg6 months ago

Unfortunately replacing the LM386 with another op-amp isn't easy to do. The pinout isn't like other standard op-amps, and you would need to change other components in the circuit.

Looks like you are in Indonesia - not sure but Futurlec might be an option:

http://www.futurlec.com/Linear/LM386N-1pr.shtml

thanks for reply. yes I'm in Indonesia. and LM386 is hard to find here. it's easier to find UA741 op-amp. at first I thought it could replace the LM386. if it is hard to do, maybe I should search and buy from the internet. I'm trying to make this for my university task. so, thanks for your advice :)

http://duniaelektro.com/product_info.php/lm386-p-476

Shafer30008 months ago

Awesome work. Trying to do something like this with an old lunch box.
Newb Question: Is C1 and C3 meant to act as a filter?

mdgrover (author)  Shafer30008 months ago
Hi there and thanks for trying this out! And you're right about the filters.

C1 is a high-pass (DC-blocking) filter that the LM386 requires because of the way we're using the chip's inputs here.

C3 is required to couple the output to the speaker - it actually forms another high-pass filter along with the speaker. If that capacitor is too small, the bass frequencies will be attenuated and the output will sound "tinny". Anything over 200μF has worked well for me.
Txdude8 months ago
Thanks for this Instructable! It worked out wonderfully, I made it as a gift for my guitar playing brother, he was blown away how good it sounded, not to mention the fact that I made it under his nose! Thanks again.
mdgrover (author)  Txdude8 months ago
That's great to hear - thanks for taking the time to share your success story!
un_named9 months ago
hello i am new to this stuff but could i use a 12v battery and a 4 ohm speaker?
Allfather9 months ago
Is there a way to add distortion or other effects? Im doing this for a science fair this is a great instructable
mdgrover (author)  Allfather9 months ago
Thanks for the kind words. There is some natural distortion in the circuit at higher gain levels, but if you wanted to you could add effects pedals between your guitar and the amp's input.
o0SLOVAKIA0o9 months ago
I know this may sound as a noob question but how would you actually ground the circuit, what would you connect the ground connections to?
mdgrover (author)  o0SLOVAKIA0o9 months ago
It's a good question actually. The ground points in the circuit all connect to each other. The negative side of the battery serves as the ground.
Allfather10 months ago
Can't find a .5 watt speaker for sp1 will .25 work?
mdgrover (author)  Allfather10 months ago
You can try, but I don't think you will get acceptable results with a speaker that small, especially at higher gain. The LM386 can actually drive about 700mW into 8 ohms, so if anything I would advise going larger than .5 watt.
tlakbir1 year ago
Hey, thx for sharing this man, I builded it and it works, but there's a lot of distortion, i tried find a way to gain mor watts or mW, I really don't know what to do.
Should I use another lm386 in parallel and une another speaker? I've got some BD135 Bd169 NPN transisor could they help gain some mW?
3W 5W??
I've got a CHMC too
xander7791 year ago
Hi, I'm using the rev. 2 diagram and I am getting a lot of distortion even at low values on the potentiometer. Do you have any ideas as to what I may be doing wrong?
mdgrover (author)  xander7791 year ago
Hello xander779 - thanks for building, and I apologize for the late reply. Your sound should be nice and clean up to higher end of the gain where some overdrive should kick in.

If you haven't solved this on your own already, I would start by double-checking for good connections throughout the circuit, whether you have breadboarded or soldered it. If you have extra parts, try replacing C1 or C3 to see if that helps.
Hey MDGrover, i have built this successfully, however i have an urgent question about the use of the pot in this schematic. Is this supposed to be used for volume or gain/overdrive? because when i turn the pot completely down, the volume stays at a certain level and never turns the volume all the way down. When the pot is turned up, at the very last 1/8 turn or so, the volume increases and becomes very distorted. I was just wondering if there was a way to wire this in this setup for volume solely. Also, would that potentially clean up the signal? Thanks for this schematic by the way. I urgently await your reply.
mdgrover (author)  colourfulmountain1 year ago
Hi - thanks for building and for sending your question. The answer can probably be found in the second paragraph of "The schematic" section above:

"Finally, the RC series circuit of capacitor C4 and potentiometer R2 provides variable gain control for the amp. I found that with these values, I could get an output range from a really clean output into the headphones all the way up to a nice distorted overdrive into the speaker. If you need to experiment with any component values with your particular instruments, those will be the ones. I found with the guitars I worked with that it took a combination of guitar volume knobs and the amplifier's gain knob (R2) to get the right sound level, especially for comfortable headphone listening."

Note that the circuit is designed to give a little overdrive (distortion) at the upper range of the gain pot, but it should cut the signal off completely at the lower end of its range. This amp will behave differently with different instruments at its input.

Try adjusting the volume knob of the guitar, and also different values for C4 and R2. You could swap in another 16v capacitor value anywhere from 1μF to 100μF for C4, and try a different pot for R2 anywhere from 5K to 50K.
rexsnel1 year ago
hi, i'm a noob and i really don't know a lot about electronics but i was just wandering if it is possible to make a uv meter using the amplified signal as input?
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