Chuck D. Bones
Circuit Wizard
I've been meaning to build this one for a while. A fairly simple FF-based fuzz with the usual Bjorn Juhl magic. He uses a JFET for Q2 which requires some cleverness because with JFETs, the source voltage is higher than the gate. A big part of getting the biasing right is choosing the right JFET. I tried quite a few, including the J113 that BJ designed-in.
This schematic was lifted from FSB. At first I thought the trace had an error because the TONE control does practically nothing. When I listened to a demo, the TONE control is quite subtle. Still, I think the connection from C5 to pin 2 of the TONE pot is a trace error. More on that later.
Q1 is a high-gain, low-noise Silicon BJT. In a regular Fuzz Face, R10 would connect directly to Q1-B. But because Q2's source voltage is higher than Q2's gate, that won't work. BJ added R3 and R4 to reduce the DC voltage going to Q1-B. I think he chose 91K and 9.1K resistors because they have brown & white color bands, colors you'd find in the arctic tundra. R5 helps stabilize the bias. C2 & R6 provide some AC bypass to increase Q1's gain. C4 & R9 perform a similar function for Q2. I've seen BJ do this in other circuits, such as the Folk Fuzz and the Pink Purple Fuzz. The FUZZ control is not as simple as it looks. It mimics the effect of the guitar's Volume control. It interacts with Q1's complex input impedance. At low FUZZ settings, The balance between bass & treble is pretty even. As FUZZ is increased the tone shifts away from bass and becomes very mid-focused. Max gain is about 70dB at Q2-D, higher than your average FF.
So how does it sound? Pretty much as Bearfoot describes it in the adverts: "...purrs like a snow leopard at lower levels and attacks with full vintage growl when pushed." Noise is practically non-existent. Even with FUZZ at zero, you have to back off on the guitar Volume to play completely clean. I've only run it guitar -> AWF -> delay -> amp so far. Probably the smoothest FF I've played. It should stack well with other pedals and doesn't have to be first in the chain like most FFs. If you have a breadboard and the time, I highly recommend building this.
The TONE network is a bit odd. As drawn, it does practically nothing. So I made a little mod. It Is The Way.
The TONE Mod
I wanted more range out of the TONE control, so I made a minor mod. I removed the wire from C5 to C6 and the TONE pot. Big difference. I ended up lowering C5 to 15nF and R12 to 3.9K (had to get that white band resistor in there). I also increased the VOL control to A100K. The modded TONE control does what the original does, but it also goes darker and brighter. C6 and R13 load down Q2's output, which not only affects the freq response but also the harmonic content at Q2-D. Breaking the connection between C5 & C6 makes the loading variable; it depends on the TONE setting. This variable loading alters the harmonic balance as TONE is rotated. It's subtle, but it's there.
Picking a JFET
We want something with Vp around 1 to 1.5V. J201 won't work, Vp is too low. MPF4393 and J112 also won't work because Vp is too high. I got good performance from J113, 2N5246 & PF5102. J113 produced the most gain. 2SK193 is another high-gain JFET if you can find one. Every JFET needs to have its bias dialed-in. The best way to do that in this circuit is to tweak R8. I ended up with a 5.90K resistor. You could put a 3.9K and 5K trimmer is series in place of R8.
My breadboard circuit looks like this. Voltages are measured with no input signal. Because R14 limits the power supply current, a shunt reverse protection diode (D1) is viable, so I did it that way. Not better, just different.
Alternate BJTs & JFETs are in the upper left corner of the board. I tried BC549C, 2N5210 & 2N5089 for Q1. They all worked equally well and each one required a different R8 to get the biasing where I wanted it. I'd say the higher the HFE, the better in this circuit. If I'd had a BC550C, I'd have tried that too. Naturally, I had to use a white LED.
This schematic was lifted from FSB. At first I thought the trace had an error because the TONE control does practically nothing. When I listened to a demo, the TONE control is quite subtle. Still, I think the connection from C5 to pin 2 of the TONE pot is a trace error. More on that later.
Q1 is a high-gain, low-noise Silicon BJT. In a regular Fuzz Face, R10 would connect directly to Q1-B. But because Q2's source voltage is higher than Q2's gate, that won't work. BJ added R3 and R4 to reduce the DC voltage going to Q1-B. I think he chose 91K and 9.1K resistors because they have brown & white color bands, colors you'd find in the arctic tundra. R5 helps stabilize the bias. C2 & R6 provide some AC bypass to increase Q1's gain. C4 & R9 perform a similar function for Q2. I've seen BJ do this in other circuits, such as the Folk Fuzz and the Pink Purple Fuzz. The FUZZ control is not as simple as it looks. It mimics the effect of the guitar's Volume control. It interacts with Q1's complex input impedance. At low FUZZ settings, The balance between bass & treble is pretty even. As FUZZ is increased the tone shifts away from bass and becomes very mid-focused. Max gain is about 70dB at Q2-D, higher than your average FF.
So how does it sound? Pretty much as Bearfoot describes it in the adverts: "...purrs like a snow leopard at lower levels and attacks with full vintage growl when pushed." Noise is practically non-existent. Even with FUZZ at zero, you have to back off on the guitar Volume to play completely clean. I've only run it guitar -> AWF -> delay -> amp so far. Probably the smoothest FF I've played. It should stack well with other pedals and doesn't have to be first in the chain like most FFs. If you have a breadboard and the time, I highly recommend building this.
The TONE network is a bit odd. As drawn, it does practically nothing. So I made a little mod. It Is The Way.
The TONE Mod
I wanted more range out of the TONE control, so I made a minor mod. I removed the wire from C5 to C6 and the TONE pot. Big difference. I ended up lowering C5 to 15nF and R12 to 3.9K (had to get that white band resistor in there). I also increased the VOL control to A100K. The modded TONE control does what the original does, but it also goes darker and brighter. C6 and R13 load down Q2's output, which not only affects the freq response but also the harmonic content at Q2-D. Breaking the connection between C5 & C6 makes the loading variable; it depends on the TONE setting. This variable loading alters the harmonic balance as TONE is rotated. It's subtle, but it's there.
Picking a JFET
We want something with Vp around 1 to 1.5V. J201 won't work, Vp is too low. MPF4393 and J112 also won't work because Vp is too high. I got good performance from J113, 2N5246 & PF5102. J113 produced the most gain. 2SK193 is another high-gain JFET if you can find one. Every JFET needs to have its bias dialed-in. The best way to do that in this circuit is to tweak R8. I ended up with a 5.90K resistor. You could put a 3.9K and 5K trimmer is series in place of R8.
My breadboard circuit looks like this. Voltages are measured with no input signal. Because R14 limits the power supply current, a shunt reverse protection diode (D1) is viable, so I did it that way. Not better, just different.
Alternate BJTs & JFETs are in the upper left corner of the board. I tried BC549C, 2N5210 & 2N5089 for Q1. They all worked equally well and each one required a different R8 to get the biasing where I wanted it. I'd say the higher the HFE, the better in this circuit. If I'd had a BC550C, I'd have tried that too. Naturally, I had to use a white LED.
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