# A TL431 Precision Reference Diode as a Fuzz



## Cybercow (Sep 12, 2022)

One of my web friends/techs/peers introduced me to the TL431 Precision Reference diode as a "fuzz" device a few weeks ago. I had stuff on my bench, but finally got around to breadboarding one of the five 'fuzz' schematics I found for the device at Freestompboxes:
TL431 Precision Fuzzes

I ordered a half-dozen of the TL431 (in the TO-92 package) reference diodes from Tayda (they're cheap enough) to try them out.

I just threw it together on the breadboard as per the attached schematic. Holy wah! It sounds just like a torn speaker - with gating. It’s not overly loud, but definitely loud enough to stand out in a live scenario. Not my cup-o-tea, but certainly a popular effect. It will definitely f**k with your mind while playing - not know when to palm mute or let it ring. And it may require one to alter 'how to play' to get some consistency.

I’m goona audit the other TL431 Precision Fuzz variants and audit them as well. If they each possess a distinction, I may do all of them up in a “Slarty Bartfast” pedal series. I found five different schematics for a TL431 fuzz - and I’ll likely play with different support component values.


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## Cybercow (Sep 12, 2022)

Adding a 2N3904 between the "Reference-In" of the TL431 and the input, (and changing the 100nF cap to 10µF), this thing gets real loud, cleans up nicely with the guitar volume pot and sounds a lot less like a torn speaker. Definitely a better 'fuzz'.


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## swyse (Sep 12, 2022)

Thanks for sharing, it's always cool to see parts be used in creative ways. I'm fascinated that these amplify at all. Might have to add these onto my next parts order to play with.


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## Coda (Sep 12, 2022)

I definitely want to play along with this…


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## Coda (Sep 13, 2022)

So what’s going on in this circuit? How does it work? Why does it work?…


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## MichaelW (Sep 13, 2022)

Well that's interesting, I have 49 of them. I needed one as voltage regulator for my GM328 build. Got them off Amazon, package of 50.....I used 1, heh.


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## Cybercow (Sep 13, 2022)

Coda said:


> So what’s going on in this circuit? How does it work? Why does it work?…


The TL431 is also referred to as a "programmable Zener". With the "Reference" input, the flow can be controlled.

In the first schematic, the TL431 alone is very "farty" and "gated" sounding. In the second schematic, with the 2N3904 inserted, it sounds a lot more like a traditional "fuzz" that cleans up nicely with the guitar's Volume pot. Not sure exactly how or why it works that way, but the schematic of the TL431 internals (as found in the datasheet) tends to indicate it is internally very much like an opamp.


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## giovanni (Sep 13, 2022)

Cybercow said:


> The TL431 is also referred to as a "programmable Zener". With the "Reference" input, the flow can be controlled.
> 
> In the first schematic, the TL431 alone is very "farty" and "gated" sounding. In the second schematic, with the 2N3904 inserted, it sounds a lot more like a traditional "fuzz" that cleans up nicely with the guitar's Volume pot. Not sure exactly how or why it works that way, but the schematic of the TL431 internals (as found in the datasheet) tends to indicate it is internally very much like an opamp.


I was skimming through the Wikipedia page and it’s basically a voltage regulator design and the page says it behaves like a transistor, which makes sense. Internally it’s a similar design to an IC but definitely different since it’s trying to do a different job. Using it as a fuzz (an amplifier) is basically abusing its designed purpose, which is a great way to make a fuzz I think!


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## BuddytheReow (Sep 14, 2022)

Sounds like a CMOS based fuzz/distortion. Not it’s intended purpose, but makes an interesting sound.


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## Cybercow (Sep 14, 2022)

giovanni said:


> I was skimming through the Wikipedia page and it’s basically a voltage regulator design and the page says it behaves like a transistor, which makes sense. Internally it’s a similar design to an IC but definitely different since it’s trying to do a different job. Using it as a fuzz (an amplifier) is basically abusing its designed purpose, which is a great way to make a fuzz I think!


I was thinking the same thing. Like the "bazz fuss" circuit, someone was thinking outside the box. The 'bazz fuss' isn't "supposed" to work - but it does. And the TL431 here is being used outside its intended design purpose - but it works.


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## Cybercow (Sep 14, 2022)

These are all the schematics I've found for using the TL431 as an amplifier (of sorts) . . . .


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## Feral Feline (Sep 18, 2022)

Cool! I just added a trio of these to my cart to play with.

Btw, it's "Bazz Fuss", note the two zeds.


Many thanks for sharing this little-known (in this context) component, and for the schematics.


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## Cybercow (Sep 19, 2022)

Feral Feline said:


> Cool! I just added a trio of these to my cart to play with.
> 
> Btw, it's "Bazz Fuss", note the two zeds.
> 
> ...


Thanks Feral! And yeah, I know it's "bazz fuss" - stoopid auto-corrupt. I took an extra moment to add it to my allowed spellings. LOL!


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## Feral Feline (Oct 4, 2022)

Hmmm, I realise too late I should've ordered at least 4 (or more in case I fry some). Must remember to order yet more.


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