Simple GGG Muff Fuzz Bias Question

Started by Phend, March 08, 2022, 12:34:28 PM

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Phend

Hello:
Building an SMD version of the GGG Muff Fuzz I have a question about bias of Q2.
Have 3409 transistors and using 12 v battery (11.4 measured)
Studying, I find that R2 is best to be left alone at 10k.
For R5 I used a 3k in place of 2k7 and getting 7.1 v at Q2 c. (11/2=5.5)
My SMD selection for R5 is 3.3k, 3.0k, 2.2k or 2.0k.

Question: Will the Q2 c voltage go Down if I use the 2.2k in place of 2k7 for R5 ?
Thanks in advance for something I should already know, but best check.




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Do you know what you're doing?

Kevin Mitchell

It would go down a few hundred mv.
Stay tuned for someone with a more detailed answer  :icon_rolleyes:
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antonis

#2
Quote from: Phend on March 08, 2022, 12:34:28 PM
Will the Q2 c voltage go Down if I use the 2.2k in place of 2k7 for R5 ?

Yes and it should be more convenient" for 12V supply.. :icon_wink:

P.S.
You can easily estimate it by some brute approximations..
Q1 Base sits at about 650mV (one VBE voltage drop) so Q2 Emitter sits at 1.3V (due to R4/R3 voltage divider)
Q2 Emitter current is 1.3/2700 => 480μA which is considered almost equal to Collector current..
So, voltage drop on Q2 Collector resistor is 4.8V hence Collector sits at Vcc - 4.8V..
For 2k2 case, Collector current is about 600μA resulting into Collector voltage Vcc - 6V..
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..