The Kronos is in fact a closed cabinet. For cooling its ITX motherboard Korg placed a little fan to let the air circulate inside the Kronos. When you boot up, all of its inside parts, electronic components, keybed, it all rises significant in temperature!
This roadmap to a Cooler Kronos has three options:
(1): "natural" airflow with two 80mm holes in the bottom plate. No fans added. System temperature did not exceed 50 °C.
(2): One 92 mm fan added (pushing air inside underneath the motherboard), Internal little fan set to "slow", system temperature did not exceed 41 °C.
(3): A second 92 mm fan installed (pulling air). Internal little fan shut down by pulling the plug of the mainboard, system temperature did not exceed 42 °C.
I finally choose for this last option. However, the little fan is turned back on, set to “slow”. Then temparature did not rise beyond 38 °C. I can hardly hear any noise coming from the 3 fans.
Measurements are from the instrument's global/menu/fan control settings, with a normal room temperature (about 20 °C) and the activities of the Kronos set to playing a combi with rithmtrack/karma for about two hours. The drawings and measurements are based on a Kronos X 73.
The holes are 80 mm in diameter, the fans are 92 mm (Coolink SWiF2-921, 16dB noise) The fans are 12V, but they work fine with 5 Volts taken from the Front panel USB-header, situated on the mainboard. With 5V power they are very very silent, but still have enough air flow to do the job.
The costs were 15 euro for the plywood, 14 for 2 fans, 2 for the grilles and 5 for the aluminium tape.
You can keep the original bottomplate for warranty reasons. When your Kronos is older, you can also make holes in the original plate. However, its better to buy a piece of quality plywood. This because the holes can weaken the original HDF board as they are situated near the edge and near the feet of the Kronos.
You need to be handy and work precise. Especially the routing (depth) has to be done precise not to deform the keybed when assembled. Aside from common tools, you will need a router with parallel guide, a jigsaw or a holesaw, a caliper and a 6.5 mm wood or steel drill. Varnish and sand the plywood before you begin.
To be honest: I was a bit afraid to do this project. I still have 2 years warranty. I could mess up? But the saying is: nothing ventured, nothing gained.
Do this project at your own risc. Static electricity from your body can harm inside electronics, use proper protection. The drawings and measurements are based on a Kronos X 73. If you plan to do this project, take you own measurements also to be sure.
What you need. Also a jigsaw or holesaw.
On the original bottom plate there is a square situated right under the motherboard. Maybe Korg planned an opening but never realised this option.
Underneath the original plate lies the new plate. This way you can use the old plate as a template and drill the 6.5 mm holes.
Draw the Line
Precise depth is important. After routing sand and varnish.
Finished woodwork versus old bottom plate.
Adhesive aluminium tape.
Finished bottom plate.
Mounting grilles on the outside.
Mounting a fan. I used a mainboard speaker connector.
option (3) with 2 fans added.
Take care, wires should not come in between the bottom plate and the sides of the Kronos! This could develop a short circuit, and -because of another distance from plate to keybed- deformation.
Ready!
I must emphasize this: the noise level is very low with these 3 fans running. It must be quiet around the house, then, with much effort I might hear something when I stick my ear in between the Kronos and the studio table.
