The Gadget Master behind the project describes it as exploring the design of a pedal for amplification and distortion, making use of a Korg Nutube.
For the first time in a while (a long while) there is a new tube on the market, the Nutube (144-8943) and (144-9016). They aim to behave just like the triode, but without a few of the more problematic aspects of a standard triode. While the Nutube behaves like a pair of triodes, the construction is different and more reminiscent of a Vacuum Fluorescent Display (VFD). There is a good reason for this and they are based on VFD technology.
He describes the device based on a Nutube as “the simplest and least restrictive amp we could pick”, and the pedal is not actually for foot control, note…
But check out the full post.
It is actually the first in a three-part series, taking the project all the way from the start to a finished working design. And it only uses free design resources, such as DesignSpark PCB.
The author is Karl Woodward, a design engineer in electronics, working with AB Open.
Why tubes? Karl writes:
Tubes do change the sound as they amplify and it’s often said the sound is “warmer”. Without getting too deep in the rabbit hole this comes from many factors; some tube amplifiers add noise, while others have a low-frequency response and amplify the bass more than treble. Maybe it’s simply the electrons are more angry in a tube than in a transistor, who knows!
Comparing the KORG Nutube to a traditional triode like the 12AX7 its gain is pretty small; the 12AX7 typically has a gain of 100, whereas the Nutube has only around 5. This will limit the gain we have in a single Nutube to around 25 maximum (assuming no other factors and using both stages). This is likely enough for most purposes and will be fine for our pedal application.
See also: New take on audio thermionic valves [Engineer in Wonderland]