DIY Bass Uke




About: I have a practical point of view for problem solving, and having an engineering education might be the cause. I love to tinker around with recycled elements, trying to find a musical use for them, although m...
Being and enthusiast of DIY musical instruments, I have postposed this instructable until having a day off.

What is a Bass Uke?
Merely a copy of the bestseller Kala UBASS, which is a short scale bass guitar in the body of an ukulele. The main component of this special bass is the string material. The strings are based in the silicon strings used by the Ashbory, later evolved to polyurethane strings when Kala launched their Kala UBASS; and Aquila has its own version of these strings called Thundergut.
The idea came to me after seeing a 3/4 classical guitar at a local shop. After comparing side by side with a Kala UBASS, I discovered to my surprise that the scale length (distance between the frets) was the same, so I had a donor to begin my DIY Bass Uke.

Note than this instrument is not a real ukelele, neither the UBASS. When Kala introduced the UBASS, they used an uke body shape because they are a ukulele brand, thus only for marketing reasons.

- 3/4 classical or steel string guitar
- Aquila Thundergut set of strings
- Bass guitar tuners

- Screwdrivers
- Electric drill and wood drill-bits
- Small rat file

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Step 1: Select a Good Donor Instrument

I found a cheap guitar at 35EUR which had the same scale length of the Kala UBASS, so it was the perfect donor guitar.

Other guitars may work, but the thing is that you must go for a guitar with a suitable string length for the polyurethane strings, or it will not work.

The proper string length is around 560 mm.

Step 2: Assembling the Tuners

First you have to remove the old tuners.

Then I just realized that it would be better if the outer strings were looped from the outside, so there is better string alignment.

At the beginning I though I would cover the holes, put a face veneer or something like that, etc. But later decided that this should be a DIY approach, and would be better to leave a rude look. 

Take care when assembling the bass guitar tuners, because with minor rotations, you can be able to fix them with three or four screws.

Also notice that the two tuners for the first and fourth strings are reversed and offset (because there was not enough space).

Step 3: Measuring

Begin by measuring the nut and bridge saddle length, which in my guitar was 45 and 70 mm.

Then, you have to measure the strings diameter. The Aquila Thundergut strings are 2,5mm, 3mm, 4mm and 5mm.

I decided to leave 5 mm from the outside of each string to the nut and saddle.

2,5+3+4+5 = 14,5 mm is the space taken by the strings

14,5+5+5 = 24,5 mm, is the total space needed for the strings and free space at each end.

At the nut, the string spacing should be = (45 - 24,5) / 3 = 6,83 mm

At the bridge saddle the string spacing should be = (70 - 24,5) / 3 = 15,16 mm

Why to make all these numbers?
Because we want to have the same free space between each of the strings. If we don´t consider the string diameter, then the centerline of the strings would be equally spaced, but the third and fourth would be closer that the first and second.

Make a template in a piece of paper with all the measures and tape it to the fretboard right next to the nut, and do the same at the brigde. Prior to fixing the bridge template mark the centerline of the place where the strings are tied.

Test with a real string if the templates are right, and if the alignment is ok with the fretboard. Remember that it´s better to check three times before cutting.

Step 4: Make the Holes at the Bridge

I used a battery hand drill with a 1mm drill-bit to make all the bridge holes. Then I enlarged the holes with a drill-bit which was 0,5mm wider that the strings. If you don´t have so many drill-bits, you can just make 5 mm holes for the four strings.

After making the holes, it was obvious that the string angle was not very good so I had to file a ramp.

Also discovered that under these innocent pearl dots, a fixing screw was hiden ;)

CAUTION: I used a black marker to paint the hole inside, and was not cautious to wait until the ink dried, so I ended with a tinted string. Wait a few minutes before inserting the strings.

Step 5: Insert the Strings

The strings go from the inside to the outside. In the Kala UBASS there is a cover at the back to be able to insert the strings from the inside, but I preferred to make it the other way and make my own knot with a washer just to ensure a better contact.

The slots at the bass tuners are not wide enough for the 5mm string so I had to file it a little bit. After some fight, the string was inside the tuner slot with enough pressure that ensures it will not slip or go out.

For the first string, I was able to make a double knot.

And voilá, you can see the four strings attached, seeing how the two outside strings are rolled from the outside and the other two by the inside.

NOTE: The black dirty marks on the fourth string are the result of not waiting the ink to dry before inserting the string in the bridge.

Step 6: How It Sounds?

At this moment I just finished the assembly, and I´m waiting the strings to settle and stabilize the tuning.

In a few days I will post a video comparing the original Kala UBASS and my DIY Bass Uke.

Thanks and hope you are able to make your own version.

You can follow me on my Ukulele Facebook Page and see my other uke things on my Ukelele website in spanish



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41 Discussions


11 months ago

Many thanks for your post, Olivergon. Here my Ubass from a 1/2 guitar (20" scale) with a Fishman presys Blend. A great sound. It came out for half price of a real ubass and 9 hours of fun work to do it.


1 year ago

a 1/4 size guitar is the one with similar string length and a similar size fret board but the scaling must be off because the fret spacing is different . kala uke bass has 16 frets and 1/4 guitar has like 19 at least. can anyone explain or help? does it even really matter?


3 years ago

I have successfully made one of these 'micro-basses' with this type of strings (of which there are now several brands) using a new, cheaply bought 5/16 classical guitar as the donor instrument. My searching found that this instrument size was perfect for the strings recommended scale length, in this case the scale is 550mm or just under 22". The wider classical neck is perfect for the fat strings, the original tuners I even used by carefully drilling out the barrels. Undersaddle pickup and pre-amp equalizer all sourced cheaply online means the entire project including donor instrument (new) was $133.00 New Zealand. So much fun to play. Been using it through large and small amps with huge satisfaction for over a year. Next project is the same idea, cheap online cello, 1/2 size is ideal for correct scale length, modified to be a micro-double-bass. The width of the neck at the nut will need some attention perhaps but this will yield a fretless bass with crowned fingerboard, lovely body and all up about double the cost (hope to keep it under 300.00 NZ) of the classical instrument hack. There is a fine instrument/maker luthier here in New Zealand who scratch makes a similar thing out of beautiful woods, calls it a 1/4 bass and it sells for about 2000 NZ dollars. If it fails to please I will reconvert to cello and sell it off, or will I? small house, many instruments, Ha!

2 replies

Reply 1 year ago

What piezo and preamp did you use?


Reply 2 years ago

Cello to bass conversion. Naively thought I was onto something newish but of course found useful info on utube and a website belonging to a creative muso named Dennis Havlena. First option I will try is, this is for a 1/2 cello, modifying nut/bridge/tailpiece to accept Fender light guage flatwounds for electric bass, all recommended by Dennis and easier than option two, my first idea, which was to fit the compound rubber type 'micro-bass' strings. There are utube vids of both ideas and In either case the volume of the body is twice or more that of the 5/16 classical micro-bass so I expect better acoustic volume, especially with the fat strings. Bit of fun, still expect to electrify and plug in.


3 years ago

I have a small guitar with a aprox. 22.5 inch scale length. I am considering converting it to a UBass type instrument. Would Aquila thundergut or Ashbory strings stretch sufficiently for this length which would range from 27 to 29 inches?

2 replies

Reply 3 years ago

New to this forum, don't know if anyone else replied but the scale length seems spot on to me if I'm right in thinking that the 27/79" refers to the total length of string needed for that instrument with the scale mentioned that should be ok as the strings come long enough unless that small guitar has a tailpiece at the bottom end which could need longer strings than if they just went to a glued-on-top bridge. I have just measured some new strings I have received (D'Addario NYLTECH EJ88UB for ubasses) and their total supplied length is just over 805mm/31" so that could do. My cello-micro-bass project will use the same strings but with the very high bridge and tailpiece I will have to develop a method to add wire tails to the strings to lengthen. Hopefully a lightbulb moment will occur as there are a few design challenges.


Reply 2 years ago

Thanks, I ended up moving the bridge so the scale(nut to saddle) was 21 inches and converted it to fretless. All is well and happy with the result. AQUILLA nylagut strings work the best. I have tried other and they break, especially the D and G strings.

So what are you building? What is a cello/bass. Will you bow it or pluck it, regarding extending the strings, maybe you could extend the tailpiece. Still anchor it over the end edge but extend it somehow to meet the strings, part way towards the bridge etc??


3 years ago

Hi, I am thinking about doing this with a small kids electric guitar. I have a few questions.

Would the Ubass strings fit into the bridge of a bass guitar?

Would the Ubass strings even work with an electric guitar? I imagine hey do since there are many electric Ubasses

Is there anything else I should be careful of?



3 years ago

Hi! I was looking for something like this!

I was wondering whether it would sound louder with a 3/4 steel guitar!

I'd like to try and make it soon!


4 years ago on Introduction

hey, where do you get a 20" scale length guitar? I'm wanting to build a ubass and can't find anything that short, even the 3/4 length acoustics are longer. Thanks for any help you can offer!

1 reply

Reply 4 years ago on Introduction

The guitar is a classic guitar but 3/4.
THe scale length has not to be exactly the same, but approximately.


4 years ago on Step 6

Here`s my version. I used a 20' scale length guitar. Thanks for the tips. I have only a problem with the "E String". Its rumbling too much when you play with punch. I will try to file the ramp like you did, or change the strings. I will also put a piezo pickup. I tested with a normal piezo for guitars and could see it works with these strings.


5 years ago on Introduction

Hi. Great project! I'm looking forward to getting down to it.

One potentially stupid question... Where you've attached the strings on the bridge: have you drilled holes through the body, fed the strings through and the attached the washer so that it's on the inside of the guitar body? Is that right?

1 reply

Reply 5 years ago on Introduction

Yes, thats right!
The original UBASS has the same method for ataching the strings, but it has a lid at the back so you can access the holes from the inside of the instrument.


5 years ago

Groovy instructible mate. I have 3/4 guitar which I was given, it's just sitting around with a broken machine head and a very slightly warped bridge (don't ask how it happened, it was like that before I got it) it's pretty useless as a guitar now, but produces a surprisingly deep tone quite nicely. This might be just the solution for it, I'd love a mini bass I can travel with.


5 years ago on Introduction

Would this conversion work on a full size guitar?? Cause I got a classical guitar laying around with a lot of bass boom but it's 66cm which misses the ubass mark by around 10cm. Will that affect it?