Design Challenge #1

Chuck D. Bones said:
Can you sketch something up?
Click to expand...
Yeah probably if I can find an eagle library part for a 4 gang pot. But it'll be a while as I'm neck deep in trying to sort out this bi-color led thing that is sadly kicking my ass (see post in the modifications section).

One thing about stacking gain stages this way is you've gotta keep the gain levels low as I think they're exponential. So even a gain stage of 10, which is pretty mild, across every stage night be too much and feedback since it'll be 10x10x10x10 (I think so at least).
 
Yup. 10x = 20dB. Gains multiply, dBs add. Comes to the same thing. 10x10x10x10 = 80dB.
To put it in perspective, low-gain distortion pedals, like the Crystal Drive, are around 40 to 50dB. BMPs are around 70 to 80dB. Biggus Dickus is around 90dB. Covert is around 100dB. SoFTii is over 125dB in Stoner mode. Thermionic and Revv G pedals are in similar territory.
 
For my schematic, I just drew four single pots and gave them the same ref des. Since I'm not routing a board, I didn't need a symbol for a 4-gang pot.

To your point, 10,000 is not too much gain for a dirt pedal. I simulated the Fuzz War v1 and it runs about 20dB per stage. For whatever reason, DBA likes running transistors in reverse-beta mode. They still work, but the hFE is very low.
 
This morning's update...

1. Added a 2.2nF cap from LEVEL pin 3 to GND. Shaves just a little off of the top end.

2. Swapped Q3 out for a leaky, low hFE MP38A. No difference in performance. Conclusion: this circuit is not sensitive to transistor parameters and just about any NPN Ge will work. Makes sense because the bias circuit is robust and Q2 can easily drive Q3 into cutoff and saturation.

I nicked my left index finger with an exacto knife 3 days ago and it's almost healed. I'll be able to give this bitch a proper workout in a day or two...
 
Pursuant to Music6000's recommendation, I have added a FAT switch and it works! Huge bottom end sludge with FAT engaged. Either way, this pedal sounds great. Definitely going to build a Vero. I added C15 & S2, bumped up C7 a little bit. The schematic shows 2N1308 for Q3, but I'm still running an MP38A there. Makes a great AC/DC sound.

Crazy Fuzz V4.1 sch.png
 
Chuck D. Bones said:
Pursuant to Music6000's recommendation, I have added a FAT switch and it works! Huge bottom end sludge with FAT engaged. Either way, this pedal sounds great. Definitely going to build a Vero. I added C15 & S2, bumped up C7 a little bit. The schematic shows 2N1308 for Q3, but I'm still running an MP38A there. Makes a great AC/DC sound.

There's no denying it, That is definately a FAT switch!!!
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