So I purchased a guitar overdrive effects kit from Alexan just for fun. If you are looking for a cheap DIY effects for your guitar, this one is for you.
Schematic
The design is not a true-bypass configuration, meaning the signal is still passing on the buffer circuit in bypass mode. What is bad about that? Well the buffer circuit cuts of some of the low frequencies of your signal and it also adds some noise to it.
At bypass mode, the low frequency cut off is just small and negligible. It cuts -3dB at around 30Hz.
Tone Control Response
Below is the simulation I made and compared it to Ibanez Tube Screamer FX pedal. Volume and gain set to maximum and the tone control set to 0%, 50% and 100%. As you can see, gain on the alexan overdrive is lower due to passive tone control design used. It also has more aggressive low frequency roll-off, which mean the alexan has thinner sound.
On the other hand, alexan has more gain on the overdrive circuit because it uses a 1M gain potentiometer rather than the 500k used in ibanez tube screamer. But do you need that high gain? I don’t think so, higher gain means higher noise.