Intro: DIY Talkbox
I was always into funky music and artists like Stevie Wonder and Zapp & Roger. So naturally, I am fascinated by the sound of the talkbox. If you have no idea what I am talking about, check out some of the talkbox videos below.
Recently, I decided to join my love for funky music with my interest in electronics and build a talkbox of my own. Usually, when I build things I do it just for fun, however, by making your own talkbox you can actually save some money. Buying a talkbox costs around 200-400 EUR, while I spent about 60 EUR for my project.
Before I started, I searched the web for tutorials and found two quite good websites which I like to mention here. GF WORKS is a website by Japanese Talkbox nerds which contains a lot of useful information on DIY talkboxes and talkboxes in general. The other site is the Talkbox FAQ by Moot Booxle, the guy also made an older youtube tutorial on how to build a very cheap "ghetto talkbox" out of an old speaker.
Step 1: Bill of Materials
- compression driver (e.g. Monacor KU-516)
- mono amplifier module (e.g. Kemo M033N)
- bipolar capacitor (depends on driver, see details below)
- 6.35 mm phone jack
- DC jack
- toggle switch
- LED + current limiting resistor
- logarithmic potentiometer (depends on amplifier)
- shielded cable
- power supply (depends on amplifier)
- PVC tube (1 - 2 m length, 8 - 12 mm ID)
1. Compression Driver
The most important part of a professional talkbox is the compression driver. The websites mentioned before give a few suggestions on which drivers to use, the golden standard would be the Electro Voice 1823M which is used in the Electro Harmonix Golden Throat series and was preferred by Roger Troutman. The driver was sold in the late 70s and you can sometimes still find these drivers on ebay. I decided to use the newer Monacor KU-516 driver which is also recommended in some of the tutorials online. The key specification of the driver are the frequency response, output power and impedance. For the frequency response holds, the wider the better, Moot Booxle recommends a driver that goes down to at least 250 Hz, the upper limit is fine for most drivers. Most drivers will have more than enough output power, for stage performances people usually use a mic to pick up the sound anyway. The impedance should match that of your amplifier. If your driver has a lower impedance it might actually damage the amplifier, a higher impedance will result in a reduced output power. There are several discussions online whether a talkbox can harm your teeth, cause headaches or even cardiac problems from longterm usage but, as far as I know, none of this is true. Talkbox legend Roger Troutman died at the age of 47, but he got shot by his brother which was unlikely caused by his talkboxing.
I used an amplifier that gives 18 W power at 4 Ohm with a 20 V power supply but since my driver has 16 Ohm and I am only using a 15 V PSU, the power will be reduced to <4.5 W. However, I found that that this is still more than enough and I never increased the volume to more than about half. Recommendations for a suitable potentiometer and power supply should be given in the manual of the amplifier. For the input connection it is recommended to use shielded cables.
Compression drivers can be damaged by too low frequencies, therefore, you should place a high pass filter before the driver. To construct a first-order (6dB/Oct) high-pass filter you just need to connect a capacitor in series with your compression driver. The resulting (3dB) cutoff frequency is f_c = 1 / (2pi*R*C), where R is the impedance of the driver and C the capacitance. Therefore, you should choose the capacitance according to the equation C = 1 / (2pi*R*f_c), where f_c is the lower cutoff frequency of your driver. For the Monacor-KU516 I calculated C = 1 / (2pi*16 Ohm*160 Hz) = 62 µF. Since the slope of the high-pass filter is not very steep it is recommended to choose a little bit lower capacitance than calculated so I used a 47 µF capacitor. The capacitor needs to be bipolar because it has to handle AC signals. If your an audiophile GF WORKS recommends a Mundorf MCap capacitor.
4. Tube Holder
Most compression drivers have a 1-3/8" 18 TPI thread, living in Germany where we are using the (more reasonable) metric system, I had a hard time finding a suitable adapter for the tube. In the end, I 3D printed my own adapter for a 10 mm ID tube, you can find the STL file attached. The thread did not fit very well on my compression driver though, possibly because the driver uses a different number of TPI.
Commercial talkboxes have inner tube diameters between 9 -13 mm. At first, I used a PVC tube with 8 mm ID and 12 mm OD but I found that it got often blocked by my tounge. I then switched to a 10/14 mm tube but it is quite difficult to keep in your mouth. You probably have to try out different tube diameters to see what works best for you. The length of the tube should be 1 - 2 m depending on where you want to place the talkbox. Keyboarders can put the talkbox close by on the table while guitar players usually put it on the ground, hence they might want a longer tube.
You may find a suitable enclosure for your talkbox in an electronics store. A housing made from aluminium would provide the best shielding and reduce possible humming noise. I made my own housing from black acrylic using the laser cutter in my local makerspace. You can find the dxf file with my housing design attached.
Step 2: Connecting Electronics
The diagram below shows how the electronic components should be connected, the schematic is quite simple. The capacitor can be placed on either side between the amp output and driver. Use shielded cables on the input side of the amplifier. Also the wires should be as short as possible, otherwise you might end up with noticeable humming noise. The LED should have a current limiting resistor connected in series. Make sure that the resistor can handle the amount of dissipated power, mine gets quite hot because the voltage drop is about 12 V. There are also LEDs with built-in resistors available. After you finished connecting everything you should test that the circuit is working.
Step 3: Prepare Housing
As already mentioned, I made the housing from 3 mm thick black acrylic with the help of a laser cutter. The bottom and sides of the housing were glued together, the top is fixed with screws using T-slots. I also had a logo engraved on the top and the current and voltage rating of the amplifier engraved on the back. If you found a suitable housing elsewhere just drill holes for all the components. For the compression driver feedthrough you might need a hole saw. The hole should be large enough for the tube adapter to fit through.
Step 4: Mount Components Into Housing
Now it is time to mount all the components into the housing. I glued the compression driver to the bottom using epoxy, make sure that it is centered with respect to the hole in the top. All other components were just screwed in. After closing the top of the housing the build is finished.
Step 5: Get Funky!
The most important thing is of course how the talkbox sounds. Hook it up to your keyboard or guitar and get funky! I have posted a video of me playing the talkbox below. Please excuse my very limited keyboard skills, I also still need to practice my enuncation which is far from perfect yet.