mzy12
Active member
Hey all. Been a while since I posted. Very busy and strange summer 
I'm looking at the BOG fuzz schematics (https://docs.pedalpcb.com/project/Marsh.pdf) and I'm wondering to myself what the goal of the buffer at the front is. I can tell it's a relatively standard silicon fuzz face (though the values R10, R11 and C14 are a bit confusing to me, I'm not sure what this achieves over using the more common approach of a pF capacitor for negative feedback), with it's main 'selling point' being that interesting buffer up front. With the voltage divider setting the bias voltage, the base voltage on Q1 is around 6.1V. (Same with output buffer Q4). On other pedals with a BJT buffer, e.g. Boss DS-1, Tube Screamer, we see a bias voltage of 4.5V. What is the goal of the higher bias voltage? I'm guessing it's to match better with a Fuzz Face's clipping profile, but I can't find anything on this online.
One other thing that gives me slight pause is the 1nF cap to ground on the guitar input before Q1. This strikes me as an intentional design choice to cut off more of the upper mids (cutoff is around 2kHz, depending on what comes before it), as opposed to something like an RF/interfence filter, like the 100pF cap that's already at the input of the pedal. Is this to make the FF topology more receptive to buffers? They generally don't sound great with an active circuit before them.
Thanks in advance for any responses
I'm looking at the BOG fuzz schematics (https://docs.pedalpcb.com/project/Marsh.pdf) and I'm wondering to myself what the goal of the buffer at the front is. I can tell it's a relatively standard silicon fuzz face (though the values R10, R11 and C14 are a bit confusing to me, I'm not sure what this achieves over using the more common approach of a pF capacitor for negative feedback), with it's main 'selling point' being that interesting buffer up front. With the voltage divider setting the bias voltage, the base voltage on Q1 is around 6.1V. (Same with output buffer Q4). On other pedals with a BJT buffer, e.g. Boss DS-1, Tube Screamer, we see a bias voltage of 4.5V. What is the goal of the higher bias voltage? I'm guessing it's to match better with a Fuzz Face's clipping profile, but I can't find anything on this online.
One other thing that gives me slight pause is the 1nF cap to ground on the guitar input before Q1. This strikes me as an intentional design choice to cut off more of the upper mids (cutoff is around 2kHz, depending on what comes before it), as opposed to something like an RF/interfence filter, like the 100pF cap that's already at the input of the pedal. Is this to make the FF topology more receptive to buffers? They generally don't sound great with an active circuit before them.
Thanks in advance for any responses
Maybe someone else will chime in to correct me.
