Design Challenge #1

[BurntFingers]

Can you sketch something up?

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).

 

[Chuck D. Bones]

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.

 

[BurntFingers]

10⁴ is 10,000. That's what I was wondering.

 

[Chuck D. Bones]

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.

 

[Chuck D. Bones]

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...

 

[music6000]

Chuck, Do you mean something like this?

 

[Chuck D. Bones]

It's like Deja Vu all over again!

 

[Chuck D. Bones]

It might need a FAT switch, Ha Ha!

You might be right. I've identified two places in the circuit where a FAT switch could be easily implemented. Hmmm, more testing...

 

[music6000]

You might be right. I've identified two places in the circuit where a FAT switch could be easily implemented. Hmmm, more testing...

CH lettering hiding behind Footswitch!

 

[Chuck D. Bones]

Saw that! Is part of the 2nd word obscured by the switch?

 

[music6000]

Saw that! Is part of the 2nd word obscured by the switch?

Could Be!

 

[music6000]

This morning's update...
I'll be able to give this bitch a proper workout in a day or two...

Reference!

 

[Chuck D. Bones]

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.

 

[music6000]

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!!!

 

[Chuck D. Bones]

 

[music6000]

View attachment 8340

View attachment 8341

I love your use of multiple components for a change of colour that do the same job!

 

[Chas Grant]

It's a rainbow of components!

 

[Chuck D. Bones]

The Chef will use whatever is in the pantry.

 

[Chas Grant]

As any great chef would

 

[Chuck D. Bones]

Finished assembly, next comes the painting. LEVEL & TONE on the bottom, FUZZ in the middle, FAT upper right. I changed C11 to 10nF and C12 to 4.7nF in an effort to give to the TONE control a little more range and a slight mid scoop when TONE is above noon.