Ever wonder how many components is the least you need to build a simple distortion effect for your guitar? The simplest I can think of will need 8 components. This is so simple that you can build the circuit even without using a PCB.
About the Circuit
The circuit consists of a common-emitter BJT amplifier and a clipping diodes. The circuit is powered by 9V battery. C1 is optional, it is only used to cut the high frequency above around 4kHz. You can decrease the value of C1 to increase the cutoff frequency of totally remove it if you don’t want any rollover of the high frequency.(refer to the frequency response simulation)
Decrease C3 if you want to cut low frequeny(bass). R4 is optional. Increase R3 if you wan’t less gain(less distortion). If you want an overdrive effect(soft clippin), transfer D1 and D2 to base-collector of Q1. D1 and D2 will be in parallel with R2, this will give soft clipping effect or overdrive.
Q1 can be any general purpose NPN transistor like 2N3904, BC548 and the like. You may also try to simulate different kind of NPN transistor using the built-in library of simetrix. There are lots of transistor you can use there.
Simulation
Input is a 100mV 1kHz sinewave.
Transient response:
AC response:
Adding Volume and Tone Controls
Adding volume and tone controls should be easy and it will only take few components. Below is the schematic
Tone Response Simulation:
You can change the value of C4 and C5 to get the tone you want but I suggest try first the values I gave them, they should be fine. You can increase C5 for more low end or bass. Decrease C4 for thinner or more treble sound. Take note that C5 has effect on the low setting of the tone knob and C4 has effect on the high setting of the tone knob.