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Make a Sweet Portable Guitar Amp

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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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jhardenberg1 month 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)  jhardenberg29 days 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

đdenda23 days 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 đdenda23 days 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?

vdo31 month 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.

Shafer30003 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)  Shafer30002 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.
Txdude3 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)  Txdude3 months ago
That's great to hear - thanks for taking the time to share your success story!
un_named4 months ago
hello i am new to this stuff but could i use a 12v battery and a 4 ohm speaker?
Allfather4 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)  Allfather4 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.
o0SLOVAKIA0o4 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)  o0SLOVAKIA0o4 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.
Allfather4 months ago
Can't find a .5 watt speaker for sp1 will .25 work?
mdgrover (author)  Allfather4 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.
tlakbir6 months 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?
mdgrover (author)  rexsnel1 year ago
That's a good question - and I'm assuming you mean a VU (volume unit) meter. You should be able to connect one to the output here as with any other audio amplifier. I spotted a couple other projects here that use the relatively simple LM3914 or LM3915 chip for this:

http://www.instructables.com/id/LED-VU-meter-that-dances-to-computer-music/
http://www.instructables.com/id/LM3915LM3916-VU-Meter/

I've made meters like these before, but I haven't done so recently so I haven't actually connected one to one of these amps.
Flyboy3881 year ago
I'm also new at this whole circuit stuff. I can solder and everything fine, but my electrical knowledge isn't great. I'd like to get a battery amp for college so I don't have to lug my big one to a dorm. Is this one easy to build for a beginner? And what is the battery life for this?
And the downward facing triangles in the diagram are ground right? I'm not used to that notation and want to be sure.
mdgrover (author)  Flyboy3881 year ago
Yes - those triangles are ground connections that should all be connected together.
mdgrover (author)  Flyboy3881 year ago
There are only about a dozen components, so if you've soldered something together of this size before I think you will be successful. If you really want to build your own but would be more comfortable using a kit with a printed circuit board there's a link to one in one of my comments below.
vde souza11 year ago
Ah, I can't reply that comment o.O

Then, here's it:
Putz! I haven't realized the LED, I messed up something so easy! xD
Thanks!
I think now it's right, I'm just waiting for the pieces, to start assemble it! ^^
Thank you again!
sorry for the bother. ^^
schema2.jpg
vde souza11 year ago
Hello Mdgrover!
I'm preparing the materials to start doing this, but I would like to make an amp more simple based on yours, with just an ON/OFF button and without the headphone output, like the step 6, but with the speaker instead the headphone.
please, can you take a look on my schematics, and see if they're correct?
thank you!
perfnschema[1].jpg
mdgrover (author)  vde souza11 year ago
Thanks for posting!

The input side of your amp circuit should work fine, but the lower-right area of the schematic needs a couple adjustments. I think you may have been confused by the wiring of the DPDT switch SW1 in the original schematic.

Here's what you need to do:
1. Connect the cathode of your LED connected to ground instead of to the amplifier output.
2. Pin 6 of the IC and the (+) terminal of C2 need to be connected to positive side of the power supply. A connection between S1 and R1 would allow S1 to turn your amp on and off.
Jimbob601 year ago
The only problem I'm having is the wiring of J2 to SW1, SP1, and the negative grouping on the board. If you could post a picture of the J2 - SW1 - SP1, that would be great. Thanks! (I'm using a 5-pin 1/8" panel mount for J2)
mdgrover (author)  Jimbob601 year ago
Hi Jimbob60 - thanks for the comments. There is a picture of my board at the top of Step 5, but it might not help much, since I brought all the wires through the perfboard and then soldered them together underneath. I do like to create a "ground rail" this way - which is actually better depicted in the perfboard illustration at the top of Step 4. That image shows the ground connection between D1, J1, J2 (and SP1), B1 and pin 4 of U1 (and C2). As you can see there, SW1 is not part of the ground circuit.

I think your best bet would be to first connect SW1 and SP1 only, and make sure you get audio at the speaker when SW1 is switched to that side (and no audio when it's flipped the other way).

Once that's working, solder your leads to J2 and test the headphone output by temporarily connecting those leads to the circuit (touching the wires to the correct points in the circuit by hand). The 5-pin jacks can be tricky, so this "trial and error" before you make the final soldered connections should help.
Hi Mdgrover

I need a little more help....

The 1/4 mono plug I am using has 3 pins. I am using trial and error to connect 2 pins together. Is this correct or should I find a plug with only 2 pins?

I also have a 1/8 stereo input which has 5 pins I have pictures of both. Do I just need to figure out how to short some pins together or am I way far off and do I need to purchase a different part?

The 1 k resistor I am using is a 1/2 watt. Your list calls for a 1/4 watt...Is mine okay?
I am breadboarding this project but am having difficulty. My led wont light up and it almost did for a second but went dim very quickly. Could this be from my 1/2 watt resistor?
I am not asking for detailed list of further instructions but would appreciate a little insight when you have the time.
Thanks
amppic1.jpgamppic2.jpg
As far as your 1/4" jack, I'm using the same one as you are. If you have a guitar cable on hand, plug it in. Then, using a voltmeter (the resistance buzzer setting works well), touch one of the probes to your cable's tip, and touch the other probe to each pin until you get a connection. To find the other pin you need, just touch one end of the probe to the inside of the jack (where the cable is inserted) and check the other two pins.

Tip: Lable one of the pins with a sharpie - a dot will do.
UPDATE

Ive actually figured some things out with a little help.
For the 1/4 mono jack in the right hand pick, I will use the two right pins only and not short any pins. The pin on the far right is connected to the insert hole which I learned is the ground and the middle pin is connected to the prong. The pin on the left is connected to a tab which is connected to the prong until a "male" plug is inserted. I will leave the left hand pin alone.

As for the 1/8 stereo plug in the left hand picture, I was told to connect the 4 left most pins together and together as a whole use this for positive and to use the far right pin as the negative. I will attempt to do this and hope it is correct.

I still have a major issue going on and can use some direction for help.
For now I have everything wired to spec except for the 1/8 plug. I have the negative from speaker going directly to breadboard instead of through 1/8 jack first. One lead from my switch is also not connected to the 1/8 plug. I assume this should be fine to test the 1/4 plug for sound.

Here is the problem

My led wont light up right away and only really does when I play the guitar. Every time I pluck some strings it lights up a little but then dims down when I stop strumming.

The other problem is that I have a lot of feedback all the time. Just turning the system on gives noise out of the speaker. I turn the pot down and it does go quieter but not really. This all happens with and with out a guitar hooked up. When a guitar is hooked up, the sound of playing is heard through the speaker but barely and is accompanied by the same unwanted noise as when no guitar is hooked up.
Any ideas?
also just to be clear the only differences in parts is:
1k 1/2 watt instead of 1/4 watt
all caps are 16 v except the 10 microFarad is 50v and the 4.7 microFarad is 25v. Could any of these parts be of fault?
Hi again

I have success. I came to the conclusion that the breadboard itself was presenting me with problems. There are many ways for wires to be loose and I believe a lot of my feedback was caused some how as well.
I assembled everything on a circuit board and have no problems at all. My led works all the time. There must have been loose connections on the breadboard.

I get no feedback anymore either. I know a breadboard can cause unwanted capacitance so maybe this was to blame.

Anyhow this was a great instuctable. I learned a lot on this build. Thanks you very much for your time.
I hope I am not breaking any rules by leaving such long posts and hope someone else can learn from them.
mattglas1 year ago
I spend 20$ on this and the first time i turned it on and it started smoking.
Must have done something wrong
Selmerman1 year ago
What does +9v to circuit mean on the diagram. We're does the wire go from the switch?
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