# Carbon Black Fuzz Trimpot



## Tornato (Apr 10, 2021)

I double checked all of my components and even swapped out the trim pot. I cant get the voltage on pin 3 of Q3 below 6.2v ???
ideas?


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## Chuck D. Bones (Apr 10, 2021)

What transistors are you using?
How about some pix?


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## Tornato (Apr 10, 2021)

using 2n3903
I can’t seem to upload a pic. Says file is too big. I will try to load it in a new program


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## Tornato (Apr 10, 2021)




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## Chuck D. Bones (Apr 10, 2021)

Now that one's too small.  PedalPCB limits picture size to 1MB.  Some folks use Google Drive or imgbb.com to host pix and then link to them.  I suspect that Q2's hFE is too high.  Can you try swapping in another one?  If can you post a higher-res pic, we'll check your resistor values.  Try measuring Q3's emitter voltage.  It won't change much when you turn the trimpot.

I usually don't have a problem posting pix here because I do a little photo editing to crop out background stuff and reduce the file size.


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## Tornato (Apr 10, 2021)

all Hfe = 105 on my  DCA55 testser


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## Tornato (Apr 10, 2021)




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## Chuck D. Bones (Apr 10, 2021)

105 is probably too high for Q2.  You can look for a lower hFE transistor or maybe it sounds ok as-is and you call it done.

One other possibility: the FUZZ pot is not 5K.  You can power-off, pull out Q3 and measure the pot it in-circuit.


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## Tornato (Apr 10, 2021)

Q3 emitter = .92v
It sounds like it going into cut-off. ( gated)
I will have to try looking at the fuzz pot


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## Tornato (Apr 10, 2021)

Well the pot in circuit is measuring closer to 8k! Pretty far outta spec I'd say


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## Chuck D. Bones (Apr 10, 2021)

As a temporary fix, you can tack in a 10K - 15K resistor from pin 1 to pin 3 on the FUZZ pot.  That will bring the resistance Q3 sees back to someting close to 5K.

Check the voltage from C to E on Q2, it might be saturating.


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## Tornato (Apr 10, 2021)

tacking the 10k across did it! it still has a gated sound no matter the voltage setting. could this be too hot Hfe on Q1,Q2? Or is this the characteristic of this fuzz?


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## Chuck D. Bones (Apr 10, 2021)

Check Q2's Vce.


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## Tornato (Apr 12, 2021)

Q2 Vce= 1.399 dcv


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## Chuck D. Bones (Apr 12, 2021)

That's where it should be.  
I dunno, maybe it's supposed to sound that way.  Is it gated at all FUZZ settings?
Let's check one more thing:
Measure the emitter voltages on Q2 and Q3 (separately).  Q2 might be close to cutoff.


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## Tornato (Apr 12, 2021)

Q2= 1.5v Q3= 5.1v


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## Chuck D. Bones (Apr 12, 2021)

R U sure those are emitter voltages?  I think at least one of them is the collector voltage.


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## Tornato (Apr 12, 2021)

Uh ya it was 🙄

Q2= .162v Q3= .933v


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