Introduction: Heinekamp

About: Currently working as a research assistant in the field of bioengineering (scaffold manufacturing, for tissue engineering), illustrating in my free time and learning to gamedev in Unity. You can find me as @vi…

Hi, folks! In my first Instructable i will show you a guitar amp i've done using the stylish Heineken draught keg as enclosure and give you the directions to do the same with your choice of keg.

Sometimes you'll notice in the photos that something looks like it's been done before, some parts will be already soldered or cut. That's because this is kind of a staged instructable, since i had the amp done before starting the ible. I actually teared it apart and put it back toghether to show you fellas how to make yours.

That said, let us begin!

Step 1: Parts Needed

To build the Heinekamp we'll need:

1x Heineken Mini-Keg (the small one, non returnable, 5L in capacity. other brands do it just as well, but don't forget the cool factor)
1x Amp circuitry
1x 120v to 9v transformer
1x Mains cable+plug
2x 3.5mm mono jack
2x 1/4" mono jack
1x Indicator LED, color to your taste
1x Toggle switch
1x 10k Log Pot
20x M5 x 25 Allen Screw
24x M5 Nut
8x M5 Washer
2x M3 Philips Head Screw
4x Rubber Bumper or any other shock absorbing bumper
4x Rubber band (the strongest you can get)
4x Speakers, various sizes, between 2 and 8 ohm, salvaged
Xx Metal mesh, enough to cover the speakers

- I'm using four speakers, in three different sizes. By using templates like i'll show, you can use as differente and as many speakers as you wish/your amp can drive/fit in the keg.

- The 2x M3 philips screw came from a random parts bin, and are used to hold the transformer. If you are using a transformer not identical to mine (needless to say, you are), look for the right screws to hold it down.

Step 2: Tools Needed

Mostly simple tools. No secret weapon here.

- Wire cutters
- Needle nose pliers
- Marker pen
- Hot glue gun
- Soldering equipment
- Rotary tool + bits
- Drawing equip (ruler, compass, pen, paper, square angle)


- For the rotary tool we'll use mostly
     • Cutting dics (fiber reinforced one are recommended)
     •  Drill bit. I used the 3mm one supplied with the tool, but that meant i had to use a....
     • Metal sanding bit, to make the holes bigger 

- To make the face plate, where the jacks and switches are installed, i used a hack saw and drill press back in school's workshop. These are not shown for the sole reason that my plate was the best i could get, kind of mockup. If i had a laser cutter and some spare acrilyc sheet at hand, the plate would be totally different.
Anyways, i still describe the process i've gone through manufacturing mine.

Step 3: Making Templates

These are actually optional, but help a whole lot when figuring out where everything will go and if it will fit. Also, taping them to the keg can make much easier the drilling and cutting operations, by puncturing guides through the paper. So, first off let's draw a template for each speaker we'll use, plus the control plate.

For the the speakers  with mounting holes:

- Measure the actual diafragm diameter
- Draw a circle with that dimension
- Draw a vertical and a horizontal line through the tiny mark left by the compass 
 - Mark the midpoint of the speaker frame sides
- Align template and speaker
- Mark mounting holes on template
- Cut template (may be better to draw a square tangent to the circle before cutting)

For the speakers without mounting holes we have to define where the screws will go:

- Same as previous, up to the drawing of the circle
- Draw a square with sides tangent to circle
- Draw the diagonals of the square; they should cross over the puncture made by the compass
- On the diagonals of the square measure 10mm outwards of the circle and mark it. That's where the screw hole will be drilled.

For the speakers of non-circular shape:

- Outline the shape on paper
- Mark the mounting holes
- Measure the speaker diafragm and transcribe it to the template
- Cut it out! 

For the control plate

- I chose a trapezoildal shape, by the dimensions of 90mm x 65mm x 100mm
- Draw the shape you chose
- Put at least one centerline to guide you when positioning it on the beer keg
- I decide to position the controls in a manner that resembles the drawing on the left in the studies, but without the distortion button and dial and bargraph.
- Cut it out and you are done.

Step 4: Using the Templates

I began the build by figuring out where everything would go, using the paper templates. After some study, this configuration came up:

- Big speaker in the center, between the two "Heineken" logos, oposite to the seam.
- Two little round speakers by the sides, near to the bottom
- Square speaker on top of the big one, also centralized to the logos.
- Control plate on top, trapezoidal shape

Before anything else, transcribe the templates to the metal screen you are using, so you can cut the protective meshes later.

That settled, mark the center line of the keg and the height where the little speakers will be centered. This can be eyeballed, but do take in consideration the topography of the keg, so the metal screen we'll use to protect the speakers fits.  

Tape the templates to the keg to make sure everything fits. Use the reference points you draw on your templates to puncture the center of holes and of the speaker itself.

Next, use the marker attached to the compass to transcribe the speaker's diameters to the keg, centered on the punctures you made earlier.

The control plate should have holes for fixing it to the keg and those are punctured on both plate and top of the barrel.

At last, the transformer will be fixed to the bottom plate of the keg, so I marked there to drill using the part itself as template.


In the first 3 photos I use a random side of the keg, free of holes, just as a demonstration, since i didn't have another keg laying around and mine was already done when I began the 'ible.

Step 5: Cutting Out

After transcribing all dimensions and puncture where to drill, its time to get to it.


HEY YOU! We'll be using cutting discs, which break  with ease when spinning at some thousand RPM. They break and the pieces fly fast enought to turn you into a pirate, full-time patch-on. Be clever and think safety first.

Go get those goggles!

Cutting the Sides

- Using a cutting disc on your rotary tool, put on some safety goggles, and only then score the whole outline of the shape you are cutting. The result of this first pass should be a hollow trench in the metal, a guide for the real cut, so steady hands are very helpful
- Now go through the outline again, but in this pass take your time and put the disc through the keg
- Complete the perimeter careful not to bend the disc and make it explode
- Sand the borders of the hole, so you can put your hands in and out without getting sliced

Cutting the Top

- Basically same strategy as for the sides, but with extra care. The metal is thicker and you are more likely to need 3 or 4 passes to cut it
- Remember to always score the cut, reducing the material thickness. If you cut through the sheet in a single spot surrounded by lots of material, if the dics happens to jolt it WILL shatter

Cutting the Mesh

- Begin with the sides. Save the holes for later, when you have only smaller (and easier) pieces to handle
- Use the back half of the wire cutter's "blade" to cut easily
- As you cut, bend the mesh away from the tool
- Cut the holes with the wire cutters. If your wire cutters has a too big of a tip or the mesh is too tight, try hammering an X-acto blade through the screen
- Measure the screens against the cut keg and check if the holes align


Main point to pay attention to: the steel of the keg is fairly thicker on the top and bottom. Because there is no curvature to help distribute the pressure from the gases inside, it is made this way. It took me two discs to complete the perimeter of this cut, the first one having shattered and the second one getting worn to half of the original diameter.  

As you cut you produce tons of a very fine grit steel powder. This powder will rust very quickly. Seriously, is like it just turns into rust, by magic. Clean it quickly with canned air or a compressor, if you have one at hand. 

Less important, but noteable, the beer leftovers inside the keg kind of rot over time. If you are using an old keg as i did, be aware of the stench that will come out of this thing. 

This video is very helpful on a great technique to cut circles, the angled cut. Check it!

Step 6: Circuitry

At some point of the build of the Little Gem i was making for this project I noticed I didn't have the necessary parts, and put it aside until i had the time to go out and buy what was missing (and let me tell you, i don't have free time, at all). Being so, i grabbed the amp circuit of the same speaker set that supplied the rectangular speaker.


What i did, and can be very helpful if you are not into etching your own PCBs:

- Pry open the box with the volume control of a pc speaker set. Inside you'll surely find the amp and, in most cases, a small transformer, volume pot and on/off toggle switch.
- Mark the pads where the power and signal come in and amplified signal goes out of the circuit. This is easily indicated by what is connected to a given pad:
     • The + and - wires of the speaker indicate the positive and negative output pads.
     • The transformer will be connected to another two pads. Those are the power input pads.  
     • The cable ending in a audio plug, the one you plug into the pc, is the raw signal input. The signal is polarized, so check the cable insulation to know what is positive, what is negative. 
- Next, rewire the pads you marked with the desired interface (jacks, plugs, etc... you could even wire a bargraph+driver to the output)

In my case the incoming 9V were only rectified when already in the circuit, by diodes. This means that i didn't have to worry about polarity when reconnecting the transformer to the pcb. Also, i added a two-pin male conector between pcb and transformer, so i could remove the control module for maintenance.  

On the other side, shown on photo 2, i made the folowing changes in order to mount the PCB to the plate:

- Desoldered and wired the original volume pot (10k, log), so i can firmly fix it in place later.
- Desoldered the orignal on/off latched switch and wired a toggle one instead.
- Removed the original speaker and soldered a 2-pin conector to the pads. This connector should be different from the power one, so you cannot plug them in a wrong and potentially damaging way. Though the wires are both orange, I carefully noted what side of the header was what polarity, and marked it

The Transformer

The little transformer was salvaged from the same speaker set that provided the rectangular speaker, the mains cable and the amp circuit. Although it was the right size for driving the amp and two small speakers, when it came to driving four coils it began to heat up. Ok, no big deal, it just got a little warm, but i'm and overkiller. Check photo 3 for the upgrades. 

Just so you know, such upgrades are totally optional. That's why i even didn't list the parts on step 2. 

Step 7: Control Plate, Assembly

Circuitry done, is time to assembly the control plate.

I use the only two original features on the PCB that i did not change as references to fix the circuit to the plate. Once in position, hot glue it.

The technique i use with the hot glue is simple, yet efficient:

- Cover the edge commom to both pieces with hot glue and smudge it with the gun's tip, so it has better adherence to the surfaces
- To cover the 6mm distance between the sides of the PCB and metal plate, smudge a small spot with glue and move the gun's tip between the pieces while gently squeezing the "trigger". The objective is to create strings of glue and thicken them until we have a solid column.
- Next just mount the other components as you would normally

There, you have your control plate.

Step 8: Speakers, Parallel, Series

Time to wire the four speakers. As simple as this can be, we still have to consider the fact that we have here three 8 Ohm and one 4 Ohm speakers. In this kind of case you must combine parallel and series wiring to approximate the desired overall impedance.

Visit this simple, yet very didactical site, to get better grip of the concepts of speaker wiring and calculate your own set's Ohmage.

The possible scenarios are:

- If we wire all of them in series, the combined impedance (sum of all of them) would be way too high for the amp to be able to drive and generate something audible, 28 Ohms. What happen is that higher impedances mean lower acoustical outputs. Its ok for a walkman to drive a 32 Ohm headset, but those do have low acoustical outputs, they're just stuck into your ears.

- If we wire all of them in parallel, the resulting combined impedance would be given by


where R1, R2, etc, are the impedances of speakers being used and n the number of speakers. With 3x 8Ohm and 1x 4Ohm, you have


which returns 1.6 Ohm. Such low inpedances can overdrive your circuit, requiring current enough to make the said magic smoke come out of your transistors, ICs, and other delicate parts.

 - Combining series and parallel wiring i can achive an impedance closer to the 8 Ohms originaly driven by the amp. Check photo 1 to see what I figured out, and than check osgeld's instructable to master that very useful inline splice!

Step 9: Fitting, Part 1 - Transformer

Finally, time to actually build the keg, attaching all the stuff we've prepared up to now.

The order of fitting is crucial, as we'll have one hand inside the keg most of the time. Save the bigger pieces for later, so you have better access. For such reason, we'll begin with something small and that is installed in the very bottom of the keg, our power house, the transformer.

Check the photos!

Step 10: Fitting, Part 2 - Speakers and Screens

Grab the metal screen you cut in step 5 and bend them into shape.

For the simple (w/o holes for fixture) speaker we have to get creative. It was originaly held down by a spring steel bar that passed under its magnet and was fixed with two screws. This fixing feature was very stiff and applied lots of pressure to the frame it was screwd on. The keg isn't able to take such pressures without denting or bowing, so i came up with the following soft fixture:

- put the screw through the metal screen
- put a washer and nut onto the screw
- position the speaker in the middle of the four screws
- catch a strong rubber band under one of the washers, pull it over and around the speaker and beneath the washer diagonal to the first
- do the same to the other diagonal, cross-bracing the coil
- tighten the nuts enough to clamp the rubber bands, but careful not to cut them

The speakers with mounting holes were much more straight forward to put in place. Screen, screw, speaker, nut, rinse, repeat. It is that easy, so i won't talk much about that. The photos tell the story.


If your washers have a "soft" side, with rounded edges, like mine did, put them on the screws with this side facing the metal screen. When you tighten the assemble, it is less likely the rubber bands snap open.

Step 11: Fitting, Part 3 - Control Plate

The rubber bumpers finally come to a use! In this project they are used to fix the control board to the keg by the same system that holds them to the cd laser carriage. 

The set up is also very simple:

- Put a screw through one of the plate's hole.
- Put the rubber bumper on the screw, with the nock on the distant side of the screw.
- Add two nuts and fix them, twisting one against the other. Take care not to squeeze the bumpers. This way we have a mounting post that wiggles, and that wiggle is what makes it fit, we need it.
- Sit the plate on top of the keg, and manage to pass the nuts to the inside of the enclosure.
-Now wiggle the bumpers while pressing them down to lock the nock against the edge of the hole. 
- Repeat for the other bumpers. On the last one you may need a small screwdriver to push the sides of the bumper, but it is no big deal.

This assembly is easy to undo, for maintenance and upgrades purposes, but is so strongly locked in place that you can lift the whole amplifier by the control plate and it won't come off.

Step 12: Final Considerations

Finally done, its time to plug in your guitar, keybord, synthesizer or whatever, and rock the Heinekamp.

Ideal for carrying around, the plastic "crown" on top of it is the ultimate handle.
The power cable is retractable, making the whole thing pretty compact for storage.

Points to be worked on the next version of it:

- Implement battery operation
- Change amp circuit to a better one, with distortion and a VU meter
- Add stereo support, so it plays decently from devices
- Add neodymium magnet to power plug, so it attaches to the barrel when cable is retracted

Some references for the next build (but you can read them right away):

- Getting Started in Audio DIY
- Little Gems

And thats all. As for questions and comments, don't get shy.

And a request for the last minute, if you liked the Heinekamp, please vote for it at the 2nd Epilog Contest. The VOTE button is right on top of the steps. Hit "home" on your keyboard and you shall see it!

Now go rock that thing.

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    4 years ago

    Estou criando um modelo tambem, logo mais posto aqui!

    Great tut!!!
    Glad to see a different twist on the Little Gem...and, a MKII for a change.
    One suggestion--and this is for the new folks. No need to add a tranny (transformer).
    You can wire a simple dc jack into the circuit, and use a wall wart--they either have a tranny built in, while others are transformerless designs.
    This will save you on some of the scrounging and certainly cut back several steps.



    9 years ago

    Ficou muito legal mesmo.
    Aqui, te mandei um e-mail mas não sei se vc recebeu o meu é tulio_po@hotmail.com


    10 years ago on Introduction

    Hey, this is an amazing design and I'd really like to base my college project on it (I've already shown it to my tutor and says it's ok as long as I can explain the maths) But I'm at an early point in my course and I'm confused at to where I would put the pots on the little gem mk2 circuit

    boa cara!
    vou fazer algo parecido.. to procurando ideias por aqui! mas a tua fiu da hora!



    Reply 11 years ago on Introduction

    Que bom que você curtiu, cara! Mais de um ano que construí essa parada, já levei pra praia e tal e tá funcionando direitinho até hoje!



    Reply 11 years ago on Introduction

    Hmmmm... I never tried it. Let me see...

    OK, I weight 65kg (not the heaviest guy in the world) and it stood well under my butts. Its just not comfortable - at all.


    curious youth
    curious youth

    Reply 11 years ago on Introduction

    Ok then when i get my heinekeg (hopefully soon.) i shall post pictures of my heinekampseat LOL


    11 years ago on Introduction

    Stunning, stunning, stunning, Gepetto!!

    I love it....it has given me the idea to turn one into a PC tower.

    Nice work!


    Reply 11 years ago on Introduction

    Thanks! (like, 7 months later =P)


    12 years ago on Introduction


    actually the mini kegs are made of steel, not aluminum. I've put speakers in a couple and I wish they were made of aluminum. Since they are steel, the magnets always fight with you when you install them!


    Reply 12 years ago on Introduction

    Hey, sorry for the misnaming of the kind of keg used. Thats a draughtkeg, or mini keg, and is pretty common in supermakets and convenience stores. Sells for about $20.


    12 years ago on Introduction

    Gepetto Father...i have a question...can you use a 9v battery for this amp???


    Reply 12 years ago on Introduction

    another thing is...where did you place those 10k pot and indicator LED??


    Reply 12 years ago on Introduction

    You do can use a 9 volt battery, but i have no clue about how long it would take for the battery to die. The circuit I used a 9V AC power input, that was then rectified by a diode bridge, but that would be easy to work around. The LittleGem amplifiers are based on 9V batteries, so if you build one, you would be using batts out of the box.
    The 10k pot and indicator LED were originally on the salvaged amp circuit i use . The LED is soldered to the pcb and past through a hole on the faceplate. The pot I desoldered from the pcb, wired it to the pcb back again and then mounted through the pcb. You can see both LED and pot on the two first photos of step 6.



    Reply 12 years ago on Introduction

    ANOTHER question again....about the little gem mkII amp....what is the actual type of capacitor used in C2 and C5/0.22 and 0.05 which of the two did you used??!!