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

xefned

xefned

Well-known member
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)."
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Also, if I'm reading the schematic right, is the CLR actually 18k?
 
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.
 
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.
 
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.
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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.
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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:
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Oh dang. That link will keep me busy.

Thanks Droogs! I appreciate all the input!
 
Try 1N4003 & 1N4148. Marc Ahlfs also likes to fiddle the bias. Note 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.
 
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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.
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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. :)

IMG_3340.JPG

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

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.
 
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.
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Thanks for sharing your knowledge Chuck. We're all a lot better off thanks to your willingness to share. I'll avoid those germaniums! :)
 
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 said:
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. 🤘
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What combination was that, if I may ask? I’ve got some muffs with clipping diode switches that I largely do not use… some nice subtle asym options may be better suited to those spots!
 
gdvsbp said:
What combination was that, if I may ask? I’ve got some muffs with clipping diode switches that I largely do not use… some nice subtle asym options may be better suited to those spots!
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On the Danube board, there are 2 sets of clipping diodes that call for two 1N914s. (4 in total.)
Instead, I used a 1N914 next to a 1N4003 in both spots. (I didn't use a switch.)

The asymmetry might be too subtle to pick out in a blind test. But I've always found I prefer asymmetric clipping whenever I have a choice.

1675643677313.png
 
Which brings me to one of my fave mods on a Big Muff. Prompted by the Colorsound Supa Tone (a modded Big Muff) I like to leave out the clipping diodes on Q2. You get slightly less compression and fuzz overall but there's still plenty to be had. But you get a more dynamic response to pick attack. I like it. It's not a mod for sludge-doomers but it's not bad for wannabe Gilmours.
 
When I've taken the diodes out of Q2 on the breadboarded muff I keep around the result was a thicker/fatter sound. It reminds me of using a 47nf cap instead of a 100nf cap in that section. I don't know if I ever tried getting more dynamic pick attack or cleaning up more with my volume knob. I need to check that out
 
C'est très intéressant!

Supa Tone Bender / Jumbo Bender is a great one for bass players, too!

Must Have a Muff (or two) built with the first clipping stage diodes on a switch.


PS:

COLORSOUND TONEBENDER SUPA VS JUMBO.png
 
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