Building the Nu:Tekt OD Kit – a Korg Nutube OverDrive Effect Pedal
Nu:Tekt kit from Korg has all the parts you need to build a vacuum tube overdrive pedal.
A lot of bits
This kit comes with a sturdy Hammond enclosure pre-drilled to accommodate the input and output sockets, the control knobs and a socket for an external power supply.
Unlike the Headphone Amp that came with some of the parts already on the PCB, the Overdrive was a bare board and, as a result, the kit includes a lot more components — including a rather daunting (for me) large bag of resistors.
My first job was to sort and label these. The Resistor identifier section of the DS Toolbox phone ap came in useful here, but I also double-checked the values with a multimeter.
As with the Amp kit, the comprehensive instructions came on a big sheet paper, but can also be found as a PDF on the Korg Nu:Tekt web site.
Putting it all together
There are options to build three different versions of the effects pedal:
- Clean: A clean boost sound with only a small amount of distortion
- Overdrive: An all purpose overdrive sound with a characteristic crunch
- Distortion: A sound that offers harder distortion
As per the instructions, I started by soldering the resistors, making sure I used the ones for the overdrive option that I had decided to build.
It was then just a case of working methodically through the guide, taking care that the diodes were mounted in the correct orientation and finishing off soldering the components with the electrolytic capacitors that, once again, have to be mounted in the correct direction. As with the resistors fitted, some of the capacitors used vary depending on which version of the effect you are building.
The 4 potentiometers that control volume, tone, shape, and gain are soldered to the other side of the circuit board. They need to line up accurately with the holes in the enclosure, so care needs to be taken to ensure that they are flush with the board and are not at an angle. As I discovered too late, it is easier to fit them at this stage, before turning the board over again and soldering the input and output sockets in place.
Putting it in its case
The foot switch and LED were fitted in the case before their respective connectors are soldered on. As the LED was a bit lose in its holder, I applied some heatshrink sleeving to hold it in place.
Now to mount the circuit board in the case. It is at this stage I realised why the holes for the potentiometers where slightly elongated — this allows the board assembly to be dropped into place and then slid backward so the rear sockets protrude through their holes. It is a very neat, snug fit and feels well thought out.
Adding the Nutube
Fitting the enclosure is made easier if the Nutube itself is added after the main PCB is in place.
The NuTube is soldered to a separate board that is connected to the main PCB with a ribbon cable. It is held in place by a strip of rubber with adhesive on both sides, that is attached before the pins are soldered. It is then connected to the main circuit board with a similar but thicker piece of rubber, so it is well protected from vibration. As Korg’s description of the Nutube states “If strong impact is applied to the unit, noise at the high frequency range may be output”.
I had problems initially getting the effects unit to work, but this was eventually tracked down to a capacitor that was most likely not soldered in place properly. Once this was rectified the overdrive performed as expected.
There is the option to run the unit in either single or double mode via a little selector switch. Flipping the switch to the double side gives a two series circuit, adding gain and volume, although this is at the expense of battery life.
The trimmer potentiometer adjusts the Nutube’s bias voltage. I adjusted it to give maximum volume — as suggested in the instructions — by setting the selector switch to the single side and then adjusting the trimmer so that the Nutube was at its brightest.
The instructions also state “The operational amplifier uses an IC socket and thus can be easily replaced”, so I assume the op amp can be swapped out to achieve a variation in the effect – something for me to try later.
In the absence of a real guitar, I resorted to using a Youtube video of someone playing guitar with a clean tone and fed that through the pedal. This gives a reasonable idea of the kind of effect the overdrive produces.
This was a fun kit to put together, albeit more challenging than the Headphone Amp. It would definitely benefit from a brightly coloured paint job and some labelling on the controls, so that it looks, as well as sounds, the part.
I intend to ask some of my guitarist friends to put it through its paces and see what they think of the sound – a much better test than the virtual guitarist I resorted to.