I Am a Man of Many Projects
Some might argue, "Too many!" As individuals, we are the sum of our ideas, that equation for me results in "technological Trotskyite with a twist." Endless revolution is consensus anarchy in loose collectives, for example the best of the best of free, free, open-source software. Such a group works tirelessly to create an app for community benefit, rewarding significant contributors with "commit privileges" on the version manager where the project is maintained, the collective of contributors having voting rights on who is doing well as a maintainer. The titles are not very anarchistic, but they actually don't have to have any meaning other than the role a person chooses to take on the project. If a fee is charged for the app, the maintainers and regular contributors, get an equal share of the profits. I just recently established a project like this, no bites yet, I've barely the skill to flesh out "HelloWorld.cpp" yet, but I'm offering to do the boring, admin work, not lead, earn my place, offer ideas. That's technological anarcho-syndicalism or, as I prefer to call it, consensus-socialist. I'm looking at founding all sort of projects this way, and my favourite to date is a "steam" driven fuzzbox.
Steam driven refers to a twin triode valve, or "tube" as the "seppos" call them, a 12AU7, low gain twin triode. Running one of these in "stavartion" mode results in a manageable gain for low voltage (gtr signal levels) clipping within controllable bounds. Originally proposed by the legendary Matsumin, starvation mode is literally running the "plate" at 9 to 12 volts. I've modified Matsumin's design to run off 9v, to keep it compatible with standard squash boxes, and added an LM7806 or similar voltage regulator to run the heater in parallel mode at 6v without frying the heater or running it too cold. You're not going to get long battery life from this, even running an alkaline battery! The current draw is a little over 300mA, most of which pours into the heaters. I've also modified the capacitances for 16kHz 3db highpass filter at 40hz, to give the pedal usefulness on bass or guitar, as per below.
How it works is like this. After the bypass switch, we enter the circuit with Matsumin's orginal high pass filter (40Hz), the 47nf capacitor and 1M resistor, to the grid of the first triod in the tube, which controls the current flow through the valve from anode to plate. (Electron convention, neg to pos.) The guitar signal modulates the tiny current through the valve to create high gain across the plate resistor, driving the signal to distortion. This is the 220kΩ resistor and 500k pot at the top of the first stage and it brings the "pain." (ie saturation, or, as you probably know it, overdrive) The bias pot at the bottom of the first stage, is a basic input gain control. The second stage is essentially an inverting buffer, to keep the phase at the pedal output in line with the pedal input. Input goes positive, output goes positive. The input/gain triode is connected to the buffer triode via another 40Hz high pass filter. Matsumin had some super-low 3dB point, but there's nothing useful in the that, and the combined effect of two, near matching filters in the chain is a sharper roll off below 40. That's a good thing for guitar or bass, trust me. Want deep subs? Use an octaver. Then finally, we have the output pot and capacitor, again, tuned for approximately 40Hz high pass. The pot reels in the saturation levels of the output, enabling the matching of output levels to input, so the next in the chain doesn't get the crap blown out of it.
For details on how starvation cathode works, see this article...
The key words we’re looking for here are “intended parameters”. Tubes were never invented to purposefully distort. Tube distortion was one of those “happy accidents” that just happened to emphasise harmonics that are pleasing to our ears, once they are pushed for headroom. Engineers and designers have exploited those characteristics for decades now, sometimes using tubes “the wrong way” in order to give us subtle harmonic distortion that has been described as “fat” or “warm”. This distortion is usually composed of even-order harmonics. Transistors have also been used much the same way, and in fact both devices (tubes and transistors alike) can produce both even or odd-order harmonics (which are commonly described as “harsh” and “shrill”).
Now, I mentioned my brand of socialism. So, while I plan to build and sell these pedals to order (hey, I live in a capitalist society, the light bulb was invented while working under gaslight), I also plan to share my designs for those who can build one of these for themselves. When they arrive from the manufacturer, I may even be willing to sell a few spare circuit boards for those who want to do the design "tube internal" with a window in the box (my preference) but some may want to build it point-to-point wired, with the "bottle" standing proud. Yikes! Please build a good cage around the glass. While the voltage is low (9v), broken glass is dangerous and, depending on where you source your 12AU7s, they may contain mercury. (Russia? also, defs with 2nd hand tubes.) Cut a view hole in the top of your 125B diecast case and glue a bit of metal mesh or clear plastic on the inside of the hole.
By convention, input on the right, output on the left, the mockup below shows an approximation of a 125B diecast box, baseplate, not shown, with the window in the top. The knobs are, top left, "The Next in the Chain", top right, "The Pain" (saturation) and, bottom left, "The Gain." The footswitch does standard bypass duties and is a 3PDT latching button, wired point to point, The 3rd switch pole switches the LED on and off.
Here is my Fritzing file, with a Gerber format circuit board artwork for the project. Yes, a Fritzing file for a valve/tube. IKR!