Design Challenge #1

I have a name: Angry Smurf. You can look up the recipe.
I sold the first one to a friend of mine. He wanted the box left bare for the industrial look.
This afternoon I added a BIAS control on the breadboard. It varies the bias on the 2nd stage to change the voicing and at the extreme end, produces a sputtering gated tone. The next build will be in a 125B enclosure (blue of course). Should have it done by the weekend.
 
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And here it is, the Angry Smurf!

Top row: TONE, BIAS
Middle: FAT switch
Bottom row: LEVEL, FUZZ

I intended to put FUZZ on the upper right, but the 4-gang pot is too tall to clear the input jack.

Angry Smurf cheers 02.jpg

Angry Smurf innards 02.jpg

The only change from the previous version was the addition of the BIAS pot. With BIAS at zero, it behaves the same as the previous version. Turning the BIAS up varies the harmonic structure. It's most apparent at lower FUZZ settings. With BIAS dimed, Q2 saturates and we get the gated, velcro fuzz sounds.

Final schematic:
Angry Smurf v4.2 sch.png
 
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With c13 going to ground there, that's forming a low pass filter with vr2 right?

Correct. C13 shaves a little more hair off of the high end. When TONE is at zero, C13 takes off about 2dB above 2KHz. With TONE at noon, it takes off 2dB at 3KHz and 6dB at 10KHz. With TONE dimed, it takes off 2dB at 1.5KHz and 4dB at 10KHz. C13's effect is audible, but not overly dark. I actually located C13 on the LEVEL pot to simplify wiring a bit.

The one I built for my friend had C10 = 10nF and C11 = 4.7nF. TONE had a little more range and a slight mid scoop in the middle.
 
Hey Chuck, with this pedal do you notice a filtering when you turn the volume knob down? I've got a pedal that ends in a big muff style tonestack then out through a volume pot, just like you have except I opted for a 4.7n to gnd a while ago. But when I roll the volume back the bass dries up and I'm having trouble finding out why.
 
I have not noticed it, but I'll try having another listen. Three things happen when you rotate the volume control on your pedal.
1. The volume changes - this is the desired effect.
2. The output impedance of the pedal changes - this can affect the behavior of the next device in the chain.
3. The loading on the pedal's tone network can change, depending on the input impedance of the next device in the chain.

There are ways to deal with all of this, but we need a better understanding of the bigger picture. Pedal circuits can be influenced by what comes before and after, so we have to think of it all as one big circuit. Sometimes the solution is a buffer at the pedal's output. You can try this experiment: connect a pedal that has buffered bypass to the output of your pedal and see if that changes the tone.

Can you provide a schematic?
 
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