Sandspur (stupid question?)

Kroars

Kroars

Well-known member
Hello all,

Im hoping one (or a few) of you could shed some light on this. I’ve been scouring the internet, articles and forums; and while I’m finding tons of info on the GE Sunface and FF circuits I don’t seem to find much on the silicon side other than to use BC108’s, BC109’s, BC183 etc. when selecting transistors. My question is: would there be a specific formula we’re looking for when choosing specific hfe for these transistors? Do we use the same ratio for Q1 & Q2 as the GE (with higher hfe)? Does it even matter on the silicon side?

The reason I ask is because I’ve built one of these and tried the aforementioned transistors, biased to 4.5v-6v but was not happy with the results. I don’t have any real experience with SF/FF pedals, and it could just be that they’re not for me.

In short: are there any suggested hfe combos I should try before giving up?

Thanks!
 
jjjimi84 said:
I always just put a lower gain in q1 and moderately higher in q2. In my build i think the bc108s were 300 and 400 respectively
Click to expand...
I think I’m referencing more the high gain versions (perhaps I should’ve specified) seeing as the 108’s & 109’s these days are a much higher hfe than the Ge formula. I’ll give the 300-400 a shot, thanks!
 
Kroars said:
I think I’m referencing more the high gain versions (perhaps I should’ve specified) seeing as the 108’s & 109’s these days are a much higher hfe than the Ge formula. I’ll give the 300-400 a shot, thanks!
Click to expand...

I have a ton of video I am editing down on building this pedal. The bias pots and clean blend play a large role in it sounding great. As always I recommend socketing and experimenting especially if this is a pedal you are new to.
 
Everybody's ears are different. I like silicon, there's something sharp and cutting about it that works great for bass (to my ears).

Kroars, I guess you have already read RG Keen's guide to the Fuzz Face circuit,
In the silicon section, it mentions use of an MPSA18, 900hFE! 🙀 Somehow I missed that the last time I read "Technology of the Fuzz Face".

Even though RG's how-to-pick-Ge-transistors suggests to get 70–130hFE, quite a number of people prefer lower than that, 50–90...
I think there's still some relevant info about the circuit itself, even if it's mainly about Ge.


I guess I'm just saying keep tinkering with it, maybe you'll find something you like that's new and different. If not, you'll still have learnt tons in the process.

PS: Meant to include this and forgot:
 
Feral Feline said:
Everybody's ears are different. I like silicon, there's something sharp and cutting about it that works great for bass (to my ears).

Kroars, I guess you have already read RG Keen's guide to the Fuzz Face circuit,
In the silicon section, it mentions use of an MPSA18, 900hFE! 🙀 Somehow I missed that the last time I read "Technology of the Fuzz Face".

Even though RG's how-to-pick-Ge-transistors suggests to get 70–130hFE, quite a number of people prefer lower than that, 50–90...
I think there's still some relevant info about the circuit itself, even if it's mainly about Ge.


I guess I'm just saying keep tinkering with it, maybe you'll find something you like that's new and different. If not, you'll still have learnt tons in the process.

PS: Meant to include this and forgot:
Click to expand...
You’ve inspired me Fig, thanks! I’ll do a bit more reading and see what I can come up with this coming weekend. Best community on the interwebs!
 
This doesn't directly apply to the Sandspur (or Sunflower) boards as they are, because the original Analogman circuit has the bias trimmer on Q2's collector, but one thing I found to be very effective when it comes to biasing a Fuzz Face without changing the expected end result too much is to actually experiment with different values in place of the 33K resistor on Q1's collector instead of the 8K2.

I literally just breadboarded yet another fuzz face to test some germanium transistors that showed up today. I couldn't bias them with stock values, so I lowered the 33K to about 27K and ended up with Q1c=0.7V and Q2c=4.75V. Sounds killer! Again, this is germanium, but the same idea applies for silicon.

Hope that helps!
 
When I think of Silicon Fuzz Faces, my mind immediately goes to David Gilmour and Meddle/DSotM. He was using the BC108/BC109 units.

Keep in mind though, he was also using a volume pedal to act as a sort of pre-gain for the Fuzz Face, especially coming off of using Germanium units.

I have a Silicon unit in the hopper with an Amperex A115 @ 121 hFE for Q1 and a number of devices, including Amperex A104 and a few other NOS silicons @ 200-230 hFE to try.
 
the thing is the silicon version just isn't going to be the germanium version ... which is why the board has a trimmer for input resistance. even if you get the gain ranges down in Ge territory and raise the input resistance, they don't quite behave the same as Ge and that's sort of the tradeoff. fwiw, I like my sandspur build almost as much as my Ge tonebender mkii and certainly a whole lot more than my Ge fuzz face which I consider to be a fuzz for people who don't like fuzz
 
Wha? I've inspired someone? No? @Feral Feline is indeed inspirational!

You have to have LOTS of fuzz pedals. Why? Because I said so!

Also, because of the variety of tones they secrete.

I HIGH-ly recommend breadboarding at least the "classics" for yourself. Pick up a "not-so-janky" rig from the store, or maybe win one?
 
fig said:
I HIGH-ly recommend breadboarding at least the "classics" for yourself. Pick up a "not-so-janky" rig from the store, or maybe win one?
Click to expand...

I second this. Breadboarding has completely changed my understanding of these circuits. With fuzz faces specifically, swapping transistors out and understanding how the hFE and leakage of Q1 affects Q2 and vice versa is fascinating. It's a seesaw.
 
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