# Danube Fuzz, Skreddy secret recipe for 'slight' asymmetrical clipping. Real? Or superstition?



## xefned (Dec 12, 2021)

I'm about to embark on a Danube fuzz after hearing some sweet Gilmourish tones from a Skreddy P19. The dude from Skreddy was kind enough to share his schematic—which rules—but he mentioned he's withholding one small piece of the puzzle, the "slightest touch of asymmetric clipping."

Do you dudes think this contributes to the sound? Or is this a subtle marketing tactic to suggest the clones can't compete with an authentic Skreddy unit?  Is this worth exploring? (I'm grateful to have the circuit available at all. I just can't help but wonder.)



> "Basically. I have a special "Skreddy" recipe for my clipping diodes for the slightest touch of asymmetric clipping that doesn't sound so different in the final mix (after 2 stages of clipping), but just adds a little bit of depth and character. I'd like to reserve that one last piece of info as my own signature touch. I suspect that older Big Muffs might coincidentally share a similar profile because older diodes were probably less precisely made and matched back in the day (much like older transistors tend to vary hugely in gains compared to their new counterparts)."



Also, if I'm reading the schematic right, is the CLR actually 18k?


----------



## spi (Dec 12, 2021)

You can socket your diodes and try out different ones.  I suspect that slightly asymmetric just means different Vfs.  You could try something like a 1n914 one side and a bat41 or germanium (lower Vf), or LED  (higher Vf) in the other.

CLR resistance is usually just whatever it takes to keep the LED from being too bright.  With some LEDs the standard 4K can be blinding, so it's not unusual to scale up the CLR until it doesn't hurt your eyes.


----------



## Robert (Dec 12, 2021)

Using a super-bright LED allows for a higher value CLR to achieve similar brightness to a standard LED.

Higher CLR means lower inrush current, theoretically this should reduce LED popping without adding any extra circuitry.


----------



## Dan M (Dec 12, 2021)

The kitrae site has a comment regarding the diodes "or try mismatched ones" which aligns with @spi reply:



			Big Muff Pi Versions and Schematics


----------



## xefned (Dec 13, 2021)

spi said:


> You can socket your diodes and try out different ones.  I suspect that slightly asymmetric just means different Vfs.  You could try something like a 1n914 one side and a bat41 or germanium (lower Vf), or LED  (higher Vf) in the other.



Yeah, thanks. I think he's talking *very slight* asymmetry. I was initially thinking to use 1N914 on one side and 1n4148 in the other direction, but even those are probably made to the same spec. Maybe I'll just measure the forward voltages on a large batch of 1n914's and pick a couple that are most dissimilar.

I suspect I won't hear the difference in an A-B test, so maybe this is purely academic.

Might even try to put a resistor inline on one side and see if that produces an audible asymmetry. 



Robert said:


> Using a super-bright LED allows for a higher value CLR to achieve similar brightness to a standard LED.
> 
> Higher CLR means lower inrush current, theoretically this should reduce LED popping without adding any extra circuitry.



Thank you. Just like spi said above. Thanks for confirming. I was wondering, "what kind of LEDs are these dudes using???" I suspect 18k won't light up any of my LEDs so I'll adjust that value for brightness. I'm still working through a bulk bag of generic LEDs I bought 10 years ago. I just ordered some superbright LEDs to see how the other half lives.



Dan M said:


> Big Muff Pi Versions and Schematics



Oh dang. That link will keep me busy.

Thanks Droogs! I appreciate all the input!


----------



## Chuck D. Bones (Dec 14, 2021)

Try 1N4003 & 1N4148.  Marc Ahlfs also likes to fiddle the bias. Note at the 56K resistor from base to gnd on the 2nd stage.  It's usually 100K.  He's running that stage colder than a typical BMP stage, which can also contribute to asymmetry.


----------



## xefned (Dec 18, 2021)

Chuck D. Bones said:


> Try 1N4003 & 1N4148.  Marc Ahlfs also likes to fiddle the bias. Note at the 56K resistor from base to gnd on the 2nd stage.  It's usually 100K.  He's running that stage colder than a typical BMP stage, which can also contribute to asymmetry.


Interesting. Thanks for pointing out that 56k. I'll explore.

I'll measure a 1n4003 and see how far "off" they are. I don't wanna go too batshit because asymmetric clipping is very audible to me. I built a Suhr Riot clone where I went gonzo with the asymmetry and I loved my 2 aystmmetric settings so much that I just removed the symmetrical setting altogether. But for this, I still want it to sound like a Muff.

Is 7mV enough to make a difference??? LOL. Probably not. 
I've got some germaniums that measure all over the map, some in the 730mV forward voltage range, some—from the same batch—up at 850mV. 





I'm leaning towards staying in the same ballpark so it's still muffy.


----------



## Chuck D. Bones (Dec 18, 2021)

A. You're making Vf measurements at much higher currents than the diodes will see in the muff circuit.  Those Vf numbers are not representative of what happens in the BMP clippers.
B. 99% of Germanium diodes are way too leaky to work in a BMP.  If you want a BIG difference in Vf, try making one of the diodes a Schottky or a series pair of Si diodes.
C. The best way to know how it will sound is to listen to it.  Calculations and simulations will only get you so far.


----------



## xefned (Dec 18, 2021)

Robert said:


> Using a super-bright LED allows for a higher value CLR to achieve similar brightness to a standard LED.
> 
> Higher CLR means lower inrush current, theoretically this should reduce LED popping without adding any extra circuitry.



I set aside a single blue LED for this project since my artwork is blue. I tested it with a 3k9 resistor and put it in my build box.

Then I read your response. Why was I skeptical? I bumped it to 10k assuming it WOULD NOT light up with a 10k.
It did.

Then I tried 18k. OK, it still lights up. I feel smarter now. It's a clear LED which is different from the colored LEDs I usually use. Interesting.


----------



## xefned (Dec 18, 2021)

Chuck D. Bones said:


> B. 99% of Germanium diodes are way too leaky to work in a BMP.  If you want a BIG difference in Vf, try making one of the diodes a Schottky or a series pair of Si diodes.



Thanks for sharing your knowledge Chuck. We're all a lot better off thanks to your willingness to share. I'll avoid those germaniums!


----------



## Chuck D. Bones (Dec 18, 2021)

Blue LEDs tend to be very bright.  Most of the time, I'm using superbright LEDs for the ON/OFF indicator and they require very little current to be blinding.  I use 10K to 22K depending on the LED.


----------



## xefned (Dec 22, 2021)

Chuck, just wanted to say thanks. I tried a combination of 1n914 and 1n4003 in both sets of diodes and the resulting Muff sounds just lovely. 🤘


----------



## Chuck D. Bones (Dec 22, 2021)

Cool.  Fellow Muff-Divers, take note!


----------

