Introduction: The ' Little Gem ' - Mini Amplifier / Guitar Amp -

This is a mini guitar amp based on the Little Gem amplifier, found at runoffgroove.com.  The unit produces only 1/2 a watt, if you want to produce a full watt to drive a 12" speaker, then I suggest building the Little Gem MKII (PDF layout attached).   The amp sounds pretty dang good for what it is, and clips can be found at the site I just mentioned above.

Listen to it here

What I want to show you (conceptually) is how to use one of these as a portable mini guitar or practice amp that already has some good sounding distortion.  

My last instructable (attempted) to do this, but I think the sound quality of that amplifier doesn't compare to this one.   The distortion tone is a huge improvement,  and the same concepts (switchable tone capacitors) can all be applied to this as well. 

You can build this with or without a Volume pot, I chose not to since it doesn't get extremely loud to my ear after playing through a Fender SS tube amp (last pic).  So I mean this isn't going to 'take over' as your main rig, and you won't be able to play to 500 people - but it's great for taking your electric guitar camping. Seriously. Try it.  It's fun, be a guitar geek.  Blaaaack Beauuuuuty is my main axe ; I hope you like ooogling her as well. 



Step 1:

Step 2: Gather the Parts

You're going to need the following


Speaker (or surround sound speaker / enclosure) 
LM386 IC 
0.01 Capacitor 
100uf Capacitor
0.047 Capacitor
220uf Capacitor
5K Linear Gain POT
25 Ohm POT (Volume) - [this is optional]
10ohm Resistor (brown / black / black / gold)

9V Battery Clip / 9V power source
ON / OFF Switch
1/4 Mono Jack

Tools:

Soldering Gun
Pliers
Drill / Bits
Guitar
Guitar Cable
Guitar Player Mojo [optional]


I say the volume pot is optional, because this thing gets cranked all the time anyway (only a 1/2 a watt remember) and I left mine out on this version.

Step 3: Prepare Your Parts, Get Ready to Assemble

Start by gutting the speaker out of your enclosure .   I highly recommend using an enclosure with a closed or open back, because your speaker will sound 10X better when it's inside of something instead of magnetized to your bench. 

Pretty much any surround sound speaker and enclosure works for this.  I know most of you don't have old surround sounds sets just laying about ; but they can be purchased pretty cheaply. I used old Kenwood surround sound boxes for my amps ; primarily because I liked the sound the speakers produced over sony's, etc... that I had.  Try all of em on your circuit before you decide to build the unit around a particular speaker.

Gather your parts, which were outlined in the last step.   Cut your perf board so it's about the size of a 9V battery.  

Once the surround sound speaker is out of the enclosure,  wire it up or use existing wire.




Step 4: Assemble

Ok, the best way to assemble this circuit is to follow the graphic.  I can't explain how to do that part, but I can give you some advice.  Don't follow my photo of the layout I used. I made a ' layout mistake' on purpose to showcase some common mistakes (too long leads).

Lay everything out on the board, and try to lay the parts out how you see them on the circuit below.  I didn't follow their layout ; by the way but went astray with my 100uf cap putting on the other side of the board to showcase a common mistake. Bad move, because those  connections are longer than they have to be which can = either feedback or radio stations coming across your signal.

POTs are numbered Pins 1, 2 , 3 looking at them with the knob face up, pin one to your left. When soldering them upside down, it's 3 2 1

Wire up your mono jack to the input, ground to the ground shown on the PCB layout.  Also wire up the positive from your speaker to the 25 ohm pot, lug 2, and ground to the PCB.  The gain pot is wired as shown in the PCB layout graphic below.

Wire your pots, a power on / off switch (just wire the 9v clip into the switch then switch to the PCB)  , the 9V clip, and your mono jack into the input and ground to the jack's connection ground on the board. You'll also need to ground your speaker to the board that you took out of the enclosure.

Drill holes for a mono jack, on / off switch, and Gain / Volume pots into your enclosure / surround sound speaker.



Test the thing once it's assembled outside of the enclosure to assure you've got it all hooked up properly. If you don't hear anything, your mono jack or your volume pot are good places to start looking for a mistake.






Step 5: Drill On!

Time to drill some holes

Take the enclosure / gutted surround sound speaker and drill the holes for your Mono input jack, 2 POTs (or one), as well as your on/off switch.  Depending on the components your drill sizes will vary, so I'll leave out that bit.

Install POTs, speaker, on/off switch, power jack, etc...  then finally the entire PCB into the enclosure .  Use zip ties on your lines to clean em up, otherwise they can rattle against the inside of the case when playing.

I removed the back of this speaker so you can see the internals of mine askew before the final assembly.

I like to use these self adhesive backed stand offs for attaching the PCB to the inside of the enclosure (away from the speaker magnet) .  This is important. 





Step 6: Play ON!!!!!

She's a pretty good sounding little amp.   That's the best part of this instructable.

I
'm really stoked with my latest attempt at the 'dirt cheap' portable amp project. This one really shines.  Inexpensive, custom portable guitar tone to the masses!  I'd post clips, but there are already some on runoffgroove.com so check em out.  They also have a ruby circuit that follows along the same lines but adds a FET filter.

Of course if you don't like the way the distortion sounds / breaks up or whatever, you can always make some value changes on those capacitors, or install a two way switch (on / on) with two capacitors wired to it so you can switch between two distortion capacitors.  I'll probably do something like that later, but I like how it sounds.

....and plus, it only cost me about $10 in parts and an old surround sound speaker.  Bonus!


Some extras?

 Well, I build custom pedals so I added my own flavor of the LPB-1  (linear power booster) circuit to mine that I can also use plugged into (any amp), and it sounds more like modern heavy on the mids distortion now.  Simply put, this circuit design gives you even more of a volume and distortion boost, and it's scalable depending on what transistor you use. 

Pay attention to H-F-E values when it comes to your transistors.  The higher the value, the more distortion / gain of the transistor.  

The circuit layout for LPB-1 is attached , I use a lower hFe valued transistor (in the 60-80hfe range) to couple with the gain that's already in the amp circuit. 

You can find a larger layout picture of the LPB-1 circuit here :

http://smallbox.zeonhost.com/projects/lpb1/index.html



Update: OCT 9, 2010 -  

Decided to tear out the LPB-1 ; and installed my own version of the Dallas Rangemaster.  Sounds pretty good because it's light on distortion / more of a treble boost for the amp... Gets louder and crunchier when it's almost max'ed.  A few layouts of the Dallas Rangemaster are attached. Please don't ask me how to make this work ; if you need to brush up on some basic guitar pedal building technique  then I suggest you start with the LPB-1 layout also below. 

Comments

author
BillyA1 made it!(author)2015-05-17

hi, just a question: will this work with an acoustic guitar-like instrument (a dulcimer) which needs more voice? thanks!

author
Phoghat made it!(author)2016-12-06

if you use a piezo pup (check ebay, come in discs attached to body inside, or a rod best under the bridge) then you can plug in to this https://goo.gl/Yd6YbT

author
Phoghat made it!(author)2016-12-06

The LM386 can run on anything from 4 to 12 volts. Is there any advantage to using a 12 volt battery instead of 9 volt?

author
jiwoduta made it!(author)2016-11-26

Hey i got confused with your schematic. Where i should put output jack or speaker? What lug mean in potensio? Its hard to find 5k potentio in my area, can i substitute with another potentio? Thanks

author
SantiagoM55 made it!(author)2016-10-26

Sorry for the noob question, but how do you connect the 5K Pot to the pins 1 and 8 of the IC, wich pin of the Pot goes to which pin of the IC? I have the circuit built on a breadboard but I don't get any sound, I think it might be the way I connected the Pot. Thanks

author
login721 made it!(author)2011-10-10

Hello , can i use a 470uF instead of 220uF capacitor at output ??

author
bigbenbeer made it!(author)2016-09-05

you can change the value of the 220 uf capacitor provided you keep it electrolytic

author
iamtoats made it!(author)2010-09-22

That sounds pretty good.
You should try running it into your Fender's speaker. (not the input, the speaker leads.....)

author
capth00k made it!(author)2010-09-22

Might try that, but with an Little Gem MKII (1 watt) , since the Celestion Vintage 30 that's in there is 60 watts I think ; and I don't see it making a lot of noise... well, not what I am used to anyway. For a practice amp with a smaller sized 4ohm speaker, this rocks. From what I understand you can run 16 ohm 2 x 12's at just above conversation levels with this Little Gem 1/2 watt. Tried running a 4ohm , 8" subwoofer speaker (35 watts I think?) from another project and it sounded O.K., but that one sounds a hell of a lot better being driven with a 30 watt head.

author
MrMindFreak made it!(author)2015-10-21

May i know the color code of Resistor 1M5 ?

author
Jonko123 made it!(author)2016-06-05

Brown, Black, Black, Gold

10R.jpg
author
bennay made it!(author)2012-09-19

HiYa capth00k, sorry for the newb question but I'm finding it hard to find the correct "gain" POT, can i just use any 5k linear pot? ebay just confused the hell out of me with ever-so-slightly different versions :(

author
Jonko123 made it!(author)2016-06-05

Hi, I made the circuit at a breadboard and sometimes sound varies, sometimes it is very distorted and bassy, others there is hum (I am using Jackson humbuckers). Help plz.(to know my cable has grounding problems)

author
dtpit made it!(author)2016-02-17

will this amplifier work with semi acoustic guitar

author
AlM33 made it!(author)2016-01-10

Hi and thx!

You've got all mixed up here on your walkthrough.

You say its a guitar amp yet there is no transistor in your layout. It doesnt amplify any guitar. Just a regular audio amp. You've got to fix your walkthrough here cuz it gets confusing for us all. Different schematics/ layouts in the begining then as you proceed to the next steps it changes :P

Anyway thanks again.

author
Brazko made it!(author)2015-02-16

can i use this for my bass Guitar ??

if cant...what parts do i need to change ?

Thanks

author

I've made the Mk2. Well, sound is going but lm386 become too hot and sound is too loud. What can be reason of heating lm386. Thank you!

author
kaji01 made it!(author)2014-08-20

I've been thinking about trying to build a portable bass amp, but I know from practical experience that a lot of low-power guitar amps can sound like crap with bass. What modifications would you recommend in this case?

author
dsanchez29 made it!(author)2014-05-30

Good Day sir/ma'am .can i ask some question.. i am making this right now cause i need a practicing amp... can you please tell me how many Volts the Capacitors .. Thanks in Advance :)

author
jfidalgo+rodriguez made it!(author)2014-04-04

I made my own one and.... It's amazing! It runs with 3 big speakers, on high level! It was hard to me because soldering gun it's too big to assemble every little thing, but i got it xD

Sorry for my bad english, Greetings from Spain =)

20140405_053801.jpg20140405_053746.jpg20140405_053850.jpg20140405_053822.jpg20140405_053811.jpg
author
avianoguitarist made it!(author)2014-02-13

Nice little tut--glad to see the Little Gem gettin' some love again!!! I do suggest updating your tut though--the gain pot is optional, not the volume...well--both are optional. Just jumper pins 1 and 8 instead of a gain pot.

Cheers!

author
jajer made it!(author)2013-02-03

Would it be possible to embed this amp into the guitar itself?

author
avianoguitarist made it!(author)2014-02-13

YES--just rout a big cavity and install.

author
Bulantuy made it!(author)2012-10-19

i build this in a past few days but my amp wont work properly i mean it sound but in very weak and distorted sound i don't put 10 uf cap in pin 1 and 8 in my country lm386 it's don't look lm386 in radioshack i live in phil

can any one help me to figure it out the problem

author
warfighter made it!(author)2011-01-03

what are the values of the resistors. pls use like nF or pF or uF
because im dutch and i cant find by these names

author
capth00k made it!(author)2011-01-03

Capacitor Values:

0.01 uF
0.047 uF
220 uF
100 uF

author
green_emi made it!(author)2011-12-03

Noob question:
are all the capacitor values on the MK2 diagram in uF aswell? its a bit confusing when some of them have units but not others

author
capth00k made it!(author)2011-01-03

10 ohm

10_Ohm_1W_Carbon_Film_Resistor_009510.jpg
author
capth00k made it!(author)2011-01-03

The Only resistor in the Little Gem layout is :

10 OHM - (brown, black, black, gold)

not to be confused with a 10K

hope this helps.

author
croberts17 made it!(author)2011-11-14

hey friend, i'm trying to do this same thing with another couple of op amps i found, 4558 chips, i have attached an image of the circuit i drew, i haven't tried it out but wanted to know if you have any advice for my circuitry :) i'm not sure what these chips can actually handle but i would love to try this. :) i've got 2 power supplys and 4 chips lol

P1010647.JPG
author
Emiliano+Valencia made it!(author)2011-01-31

how can I add a Headphones jack????

author
smash10101 made it!(author)2011-10-12

try putting it where the speaker would go, or add on on/on switch where one goes to the speaker & one to the headphone port

author
LkArio made it!(author)2011-04-27

I connected this to a single 4 ohm speaker, it sounded better, pretty much. Better than the two 4 ohm speakers on series that I had before...

author
mmeeker made it!(author)2011-04-20

you guys should all check out the tube reamer effect at http://runoffgroove.com/tubereamer.html

author
mmeeker made it!(author)2011-04-03

Man i had to unsolder my board once but i finally got haha i couldn't figure out where you were going because you didn't list a - on the layout but i got it now it sounds great

author
capth00k made it!(author)2011-04-20

Ohhhhh, your ground connections. Gotchya.

author
mmeeker made it!(author)2011-04-13

oh i'm sorry man i don't know much about this kinda stuff at all this was my first project but i thought the LM386 had a V+ and V- but it only has a V+ lol like i said my bad. Now that i know how to do this it has helped me with other projects i've been working on like a LM3886 Amp and a couple of pedals.

author
capth00k made it!(author)2011-04-13

Right on man. What did I forget to list ?

author
LkArio made it!(author)2011-04-19

Hehe, I did it. It was a lot louder than I expected for the LM386N-1 version, and it seemed to drain 1V off my battery after about 20 minutes. The distortion is awesome. Nice instructable.

author
capth00k made it!(author)2011-04-20

Right on man. Enjoy. I like this Little Gem design for the same reason - distortion sounds great! Just enough, and not too much :)

author
LkArio made it!(author)2011-03-20

Nice instructable!
Would it be possible to have good distortion with the LM386-3 or LM386-4 version of this chip?

author
black_dot made it!(author)2011-03-13

hi , im new to electronic so i have no idea how to do this , how do i connect the components together if im not using the volume control

author
reginaron made it!(author)2011-01-28

Hi. Mabye your'e the right person to ask.

I have a cheap AC/DC, 2 speaker set ,that can be used either trough a PC, or a CD player. Amplified system.
This ( main speaker unit), has a 1/8","mic" input on the front and a 2nd on the back.
So I attached an 1/4f -1/8 m,adapter from my guitar,and cord to the " mic ",in the front,and back. ZERO sound.
Power / Vol all good. Is a preamp neccessary?
Thanx for any suggestions.

RJ

author
emmett1989 made it!(author)2011-01-03

i cant find 0.047uF in my nearest store? can i change this value?

can i use 10k pot for the volume pot and gain pot?

author
emmett1989 made it!(author)2011-01-02

Hi capth00k, can use this project as pre-amp?

author
capth00k made it!(author)2011-01-02

Sure, but I would (personally) build something like an Alembic Stratoblaster for that. A really simple tag board layout is attached of the Alembic. Great for screaming guitar tones or mild overdriving of amp (depends on how set)

AlembicStratoblaster-IvIark.png
author
PieMaster777 made it!(author)2010-12-21

Your Black Beauty is Beautiful, and the amp is nice too!

author
capth00k made it!(author)2010-12-21

Thanks mate, have to gloat a tad and show off the gear for all us gear slutZ. I still can't believe they're all mine .... ! lots of hard work !!

Peace, Capt :)

author
da+animal+freak made it!(author)2010-11-24

great instructable. what was that little tune you played on the amp? i really like it! if you have the tabs please post it on here, thanks!

author
capth00k made it!(author)2010-12-11

The clip wasn't me, it was actually from the makers of the Little Gem MK II circuit which I used to assemble the portable amp.

About This Instructable

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Bio: I am a musician, internet developer, and a hobbyist pedal builder.
More by capth00k:Fixing an iMac g5 Power Supply using an ATX (pc) PSUThe ' Little Gem ' - Mini Amplifier / Guitar Amp -Portable Guitar Amp with distortion / Bass Amplifier - 9v / LM386 IC
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