BIAS: All guitar pedals run on X amount of volts, and in analog pedals, especially transistorized pedals like this one, changing the recommended supply voltage can yield interesting results. This control loads down the voltage from the supplied 9V all the way down to just under 5V. Sonically, this means a "leaner", "smoother" tone that many have compared to video game sounds. Maxing this control out pushes the circuit into a sweet, sputtery texture that evokes slight octave-down tones. In this setting, you have to really dig in while playing to get the most out of it, but in doing so, you shall be handsomely rewarded.
Note: For all you experimentalists out there, the Bias control destabilizes the entire circuit and gives you a sort of "controlled chaos" while playing. However, if your Bias knob is maxed when you plug in the power cable, the pedal will oscillate and provide synth and drone textures until you stabilize it by turning the Gain knob. This will not occur again until power is unplugged and plugged back in with Bias maxed.
GAIN: Many gain controls are tied to a specific semiconductor, and some are wired like volume controls separating one part of the circuit from the rest. This one is wired as the latter, but it separates the guitar from the rest of the circuit. In fact, it's the same as your guitar's volume knob! If you keep this knob maxed, you can control the level of gain with your guitar.
The Knight School Fuzz accepts a center-negative DC power supply capable of supplying 9 volts and at least .5mA of current (over is fine). Plugging in anything other than this (center-positive, AC, higher voltage) will damage the pedal, maybe even beyond repair. Check your supply and make sure it says all the right stuff. Plugging in the wrong supply will void the warranty and possibly summon a puff of ozone-tinged smoke. Trust me, you’d hate it.
DIY KIT INFORMATION
The circuit board has everything labeled as to what part goes where. You'll find the below image very helpful to identify what parts are what. There's also a video below showing you how the process will go.
WATCH IT BEING BUILT
A BIT ABOUT PARTS
Identifying the resistors
Identifying the ceramic caps
470p: (short legs)
47p: (long legs)
Here is a list of mods that you can try if you're feeling it! We only provide you with the components for our build, but feel free to try these mods with other parts you obtain and we are happy to chat with you about how it's going!
A quick primer:
1. The primary component of a transistor that concerns us is one called hFE. Without getting into the fine print, hFE essentially means how much gain a given part has. Different hFE values affect the biasing of whichever circuit block the part is found in.
2. Transistors consist of three pins, labeled “emitter”, “base” and “collector”. What these actually mean isn’t vital for our purposes, but whether or not replacement transistors will function in this circuit depends on making sure the emitter, base, and collector pins of the new transistor go to the same circuit board pads as the stock transistor. On the Knight School board, the pins of the 2N5088 left-to-right are emitter, base, collector. To find out if the transistor you plan on substituting matches, try Googling “(your part number) datasheet”. Even if your part doesn’t slot right in, you can manipulate the legs so that they do.
The 2N5088 does most of the heavy lifting in this circuit, and it is considered to be a “medium-gain” device. You can replace this part with any transistor you like, so long as the replacement is an “NPN” type. A transistor being NPN or PNP is very important, so this designation will never be hidden. And because the bias on this circuit is variable, it will always work. Whether or not it will work “well” in all bias positions, that’s a case-by-case basis.
2N5088 transistors typically have around 400 hFE. MPSA14 transistors, for example, have around 10,000 hFE. Experiment!
Bias max and min:
The 1K8 resistor above the 2N2907A board footprint controls the minimum resistance for biasing. When the Bias knob is rolled all the way back, the transistor is getting the least amount of resistance, which in this case is 1800 ohms. You can adjust this value to be lower or higher to your tastes. Do you like the way the pedal sounds when Bias is set a third of the way up? That value is 1800 ohms plus roughly one-third of the Bias potentiometer, which is 33,000 ohms. If you replace 1K8 with 33K, you will have made the lowest knob position equal to one-third up on the stock circuit.
On the other hand, you are welcome to swap out our stock A100K potentiometer for a lower or higher value. “A” refers to the sweep of the potentiometer, switching it out for one with a “B” or “C” will still work, but the sweep will be uneven.
One of the easiest modifications you can do to this and any other circuit is that of swapping out the clipping diodes. These parts take a boosted signal and shear off the peaks and valleys, reducing amplitude and resulting in a “clipped” signal that amounts to a more saturated sound. Common clipping types are germanium diodes, LEDs (what did you think the D stood for?), and the silicon diodes that we include in the kit (1N4148). But you don’t even need to buy anything extra to try this mod out; simply leaving the diodes out is an option too, letting the full signal through to the output.
NOTE: because amplitude is colloquially known as “volume,” cutting the peaks from the signal with diodes results in a lower volume. Germanium and Schottky diodes clip at the lowest thresholds, so you will get a more heavily clipped signal with the tradeoff of less volume. Leaving the diodes out makes the signal considerably louder, you have been warned!
Input and output caps:
Both 100n capacitors in this circuit can be reduced or enlarged to suit your tastes. Smaller values yield less bass and slightly less gain, and the converse is true for larger values.
The 2K2 resistor in this circuit sets the amount of gain when the Gain knob is set at its lowest. Replacing this resistor with a piece of wire will cut the signal entirely when this control is set to zero. Setting it to a higher value will reduce the range of the Gain control. If the lowest setting on the Gain knob isn’t of use to you, gradually enlarge this value until you like the entire sweep.