Twin Face pre build questions

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Drlufk00

New member
I am looking at this as my next build and have some questions for people that have accomplished this project before.

1.) what are good alternative transistors for the PNP Germanium side if I decide to deviate from the build specs?

2.) What are good HFE values for both sides (Q1/Q2 and Q3/Q4). In my previous germanium build I settled on Q1 of 80 and Q2 of 138 (NPN 2N169)

3.) Biasing… I have seen other threads about trouble getting the PNP side biased correctly. Any recommendations for replacement components to achieve this? On the biasing subject… in the past I have like to use an external 10k trim pot for the bias, this would work in this build too correct? Or would it not be recommended due to have 2 trim pots vs 1?
Thanks in advance!
 
The main thing about fuzz faces (and tone benders, Zonk Machines, Fuzz Rites) is: the key is to buy a bunch of transistors and experiment a lot. The leakage affects how the fuzz face will clean up, how gradual is the cleanup, the texture of the decay. The internal capacitance of the transistor will partially dictate how dark or bright your fuzz is going to sound. There isn’t a exact formula, you can find really awesome results going with gains and leakages well above or below the anecdotal values you will see on forums. If you use the search function you will find lots of references for what people think are good sounding transistors… I’m usually partial to the Japanese germanium, but YMMV
 
If I understand this properly, its all about picking your transistors and then the biasing is just in the trimmer - I think I saw a post about a 10K trimmer not having enough range and they had to change it to 20K?
 
I am looking at this as my next build and have some questions for people that have accomplished this project before.

1.) what are good alternative transistors for the PNP Germanium side if I decide to deviate from the build specs?

2.) What are good HFE values for both sides (Q1/Q2 and Q3/Q4). In my previous germanium build I settled on Q1 of 80 and Q2 of 138 (NPN 2N169)
wheelie life
3.) Biasing… I have seen other threads about trouble getting the PNP side biased correctly. Any recommendations for replacement components to achieve this? On the biasing subject… in the past I have like to use an external 10k trim pot for the bias, this would work in this build too correct? Or would it not be recommended due to have 2 trim pots vs 1?
Thanks in advance!
Click to expand...
For the PNP germanium side, transistors like AC128, AC176, 2N404, or even Russian MP38 types can work well if you select for low leakage. HFE values around 70–100 for the first transistor and 110–150 for the second usually give good results, similar to what you’ve already used. Biasing can be tricky with germanium, but adding small emitter resistors or slightly adjusting collector resistors helps stability, and using a 10k trim pot for biasing is fine. Having two trim pots isn’t an issue as long as you adjust them carefully and allow for thermal drift, which is common with germanium devices.
 
I have built a handful of these, with different setups to get variations in the sound. I found breadboarding was important, but then I snagged a Huntington Audio Fuzz Explorer from LoveMySwitches, and that lets experiment with transistor sets and dial in all of the resistors really nicely.
I have a lot of Russian Ge's that are well below the "normal" range, and they work fine for me. I have found that, beyond the norm al trim pot, adjusting R4 below 100K makes a huge difference in being able to establish bias. I am strongly of the opinion that the "preferred" values just reflect the gains that are aligned with the standard resistor values. You can make anything work with adjustments to the resistors.

I also found, using the HA Fuzz Explorer, that changing capacitors to adjust the filters can have a major impact on the sound, and is another way to vary the two sides of this circuit.

And finally, I went totally off the reservation on my last build's NPN side, and copied the components and values from the Chthonic Fuzz (Fudge Round PCB) minus the tone circuit. Although I have imbalanced volumes, I have setup where the Si side is bright and bitey, and the Ge has more bass (but not mushy).
 
Drlufk00 said:
Also, does anyone have a Tayda drill template for this build?
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PS Drill Pattern
This is my drill pattern. I move the LED around from the basic layout, and also this is setup for Neutrik NMJ style jacks (chrome nose) and a Lumberg 1614-09 style DC power.

Looks like I never posted a build report with my last iteration of variant components (not really modifications I think)
 
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