Carbon Black Fuzz Trimpot

[Tornato]

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?

 

[Chuck D. Bones]

What transistors are you using?
How about some pix?

 

[Tornato]

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

 

[Tornato]

 

[Chuck D. Bones]

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.

 

[Tornato]

all Hfe = 105 on my DCA55 testser

 

[Tornato]

 

[Chuck D. Bones]

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.

 

[Tornato]

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

 

[Tornato]

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

 

[Chuck D. Bones]

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.

 

[Tornato]

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?

 

[Chuck D. Bones]

Check Q2's Vce.

 

[Tornato]

Q2 Vce= 1.399 dcv

 

[Chuck D. Bones]

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.

 

[Tornato]

Q2= 1.5v Q3= 5.1v

 

[Chuck D. Bones]

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

 

[Tornato]

Uh ya it was

Q2= .162v Q3= .933v