Archive for January, 2008
Friday, January 11th, 2008
Voodoo Lab Overdrive
I have various reasons for putting this one together. My interest was peaked when the Voodoo Lab Overdrive was associated recently with the Fulltone OCD. I was also looking for a relatively simple circuit with op-amps that I could use for an Eagle layout tutorial that I plan to write. In addition, I have been working up my understanding of op-amps through writing a series of tutorials and the divided negative feedback tools are really useful with this circuit.
There are a bunch of mods to consider with this circuit, all of which have been applied to other stompbox circuits over the years. And if the reports are accurate, similar mods appear in the OCD as well. … more …
Tuesday, January 8th, 2008
Op-Amps 4: Divided Negative Feedback
Simple negative feedback, connecting the output to the inverting input, makes an op-amp into a unity gain amplifier. In that setup, all of the output goes to the inverting input. If instead the amount of feedback is reduced, through a voltage divider, then the gain of the op-amp circuit becomes greater than one. This may be the most common way op-amps are used for amplification in stompbox circuits. In addition, by adding some capacitors to the voltage divider, the gain also gets some tonal character that is the foundation of dozens of famous distortion and overdrive pedals (think Boss, Fulltone, Ibanez, Marshall, Proco, Voodoo Labs, …). … more …