# SandSpur Fuzz biasing?



## MichaelW (Jul 8, 2022)

Hey guys, 

Just got my SandSpur board in the mail today and putting together the parts for the build. (Recommended by @thewintersoldier, thanks Chris!)

Any tips on biasing Q2? I'm a little confused by how the external "Sun" pot and internal 5k trimmer and R3 interact.

From the schematic it looks like 3 resistors in series to me, do I have that right? 

I'll be using BC108's per the BOM.

TIA!


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## Big Monk (Jul 8, 2022)

I usually target between 1.35-1.5 vDC on Q1c and 4.5-5.75 vDC on Q2c.

The internal trim is meant to set the range of the external control. If you wanted to have Q2c in Tonebender MK 1.5 territory for voltage, you could turn the internal trimmer all the way off to shift the adjustment range on the external toward higher voltages.


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## Coda (Jul 8, 2022)

Big Monk said:


> I usually target between 1.35-1.5 vDC on Q1c and 4.5-5.75 vDC on Q2c.
> 
> The internal is meant to set the range of the external trim.



I concur…except I don’t think I’ve never measured Q1 on a Fuzz Face. The internal trimmer sets the bias, and the sun dial control adds a bit more or takes a bit away, to taste…


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## Big Monk (Jul 8, 2022)

Coda said:


> I concur…except I don’t think I’ve never measured Q1 on a Fuzz Face. The internal trimmer sets the bias, and the sun dial control adds a bit more or takes a bit away, to taste…



Tweaking Q1c voltage can help you dial in the overall noise and cleanup profile but it's more of a 5% type of tweak.


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## Coda (Jul 8, 2022)

Make sure you socket the transistors, since you can use lots of different combos, as they all sound different. I prefer BC109C, personally. BC108 is a the standard, 109c is a little hotter/aggressive. BC183 (I think it is) is darker, and a little thicker…though not as fuzzy…


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## Big Monk (Jul 8, 2022)

Coda said:


> Make sure you socket the transistors, since you can use lots of different combos, as they all sound different. I prefer BC109C, personally. BC108 is a the standard, 109c is a little hotter/aggressive. BC183 (I think it is) is darker, and a little thicker…though not as fuzzy…



You can use the gain bucket designators (A, B and C) to drive the overall gain of the pedal. The A range will probably exhibit a lot of the characteristics @Coda describes of the BC183, the B range will be the sort of standard silicon Fuzz Face sound and the C range will give more gain and "sizzle".


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## MichaelW (Jul 8, 2022)

So I have 3 BC108's. 2 of them measure in the 470's and one of them 780. My plan is to use the 780 in Q1 and one of the others in Q2.

I do intend to socket and try some other SI trannies as well.


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## Big Monk (Jul 8, 2022)

MichaelW said:


> So I have 3 BC108's. 2 of them measure in the 470's and one of them 780. My plan is to use the 780 in Q1 and one of the others in Q2.
> 
> I do intend to socket and try some other SI trannies as well.



Try the 470s in Q1 and Q2.

EDIT: 470 is approximately at the high end of the B range and low end of the C range so it should have a good middle ground between the standard Si tone and a more sizzlely 109C type.


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## Coda (Jul 8, 2022)

Also, just a comment of my own; I biased mine to 5v exactly, and I have the sun dial at about 2:30…


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## MichaelW (Jul 8, 2022)

Big Monk said:


> Try the 470s in Q1 and Q2.
> 
> EDIT: 470 is approximately at the high end of the B range and low end of the C range so it should have a good middle ground between the standard Si tone and a more sizzlely 109C type.


I've also got some assorted BC109's and BC107's to try once I get it all working. But thanks for the tip! I'll start with your suggestion.


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## Big Monk (Jul 8, 2022)

MichaelW said:


> I've also got some assorted BC109's and BC107's to try once I get it all working. But thanks for the tip! I'll start with your suggestion.



The numbering actually doesn’t really matter at all for these types of circuits, i.e. the BC10x series have mostly equivalent specifications with the exception of specific voltage specs, etc. 

The gain “bucket” designator says more about the transistor in that series than the number.


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## Big Monk (Jul 8, 2022)

thewintersoldier said:


> I set mine on a shelf and haven't touched it in forever. RIP my fuzz face☠️🙏⚰️🪦🥀😭



Did you ever end up building a JHF1 clone?


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## Big Monk (Jul 8, 2022)

thewintersoldier said:


> No, been too busy building memory men and electric mistresses 🤷



True, true! You right!


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## Coda (Jul 8, 2022)

thewintersoldier said:


> No, been too busy building memory men and electric mistresses 🤷



Drag…


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## Coda (Jul 8, 2022)

thewintersoldier said:


> Someone had to leave the kids table and build real pedals 🙄🤡🤣🤣



There’s nothing wrong with building another rat/TS variant…


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## Big Monk (Jul 8, 2022)

thewintersoldier said:


> No there isn't. Some people want to stay on the ground, some of us want to touch the sky



To be fair, your circuit won’t work without the ground so...


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## Coda (Jul 8, 2022)

thewintersoldier said:


>



I think that was a Mu-Tron III, wasn’t it?…


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## Robert (Jul 9, 2022)

thewintersoldier said:


> Someone had to leave the kids table and build real pedals 🙄🤡🤣🤣





thewintersoldier said:


>



😬

For future reference, it's probably poor judgement to reference "leaving the kids table" then post an R Kelly meme two posts later.

Context is key.




Only kidding, I know there were like, trim pots that had to be turned one way or the other..


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## HamishR (Jul 9, 2022)

I've been meaning to build a Memory Man but keep forgetting to.

I've been thinking about studying how this stuff works because I still have no idea why it does. But I'm afraid that if I learn how it works then it won't . It _is_ magic, right??


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## giovanni (Jul 9, 2022)

HamishR said:


> I've been meaning to build a Memory Man but keep forgetting to.
> 
> I've been thinking about studying how this stuff works because I still have no idea why it does. But I'm afraid that if I learn how it works then it won't . It _is_ magic, right??


Science is more art than science. Even if you learn how it works, it’s still quite mysterious. Semiconductors are all based on quantum mechanics so…


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## Big Monk (Jul 9, 2022)

giovanni said:


> Science is more art than science. Even if you learn how it works, it’s still quite mysterious. Semiconductors are all based on quantum mechanics so…



This.

I was trained as an electrical engineer and there were times that reading my textbooks felt like reading Lord of the Rings or the Old Testament or something. 

At the quantum level, shit kind of IS magic.


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## fig (Jul 9, 2022)

giovanni said:


> Science is more art than science. Even if you learn how it works, it’s still quite mysterious. Semiconductors are all based on quantum mechanics so…


That’s why I learned quantum mechanics first, to have an edge in pedal-building.


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## Robert (Jul 9, 2022)

This is how I felt when first learning how CRTs worked way back in the day.

So we're firing an electron beam using 30,000V and bending it with electromagnetism to deflect it all over the screen?   Which then _glows_ in different colors when it's struck?

Right. It's time to stop watching so much Star Wars, tell me how they _really_ work.


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## ICTRock (Jul 9, 2022)

"real pedals" where's the lovetone then?


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## giovanni (Jul 9, 2022)

Big Monk said:


> This.
> 
> I was trained as an electrical engineer and there were times that reading my textbooks felt like reading Lord of the Rings or the Old Testament or something.
> 
> At the quantum level, shit kind of IS magic.


Same here. My professor just started talking about the NP junction and how electrons would do all kinds of crazy shit and I thought it was some weird alchemy nonsense 😂


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## Robert (Jul 9, 2022)

Oh man I had the hardest time with PN junctions.... So like, we trickle a few electrons (or holes, depending on who showed up that day) through here and they're all like "Hey guys, let's jump off this bridge together!" and then all their friends follow along and... what?    This school sucks, you guys are just making this s**t up as we go along.


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## benny_profane (Jul 9, 2022)

Serious question for folks that studied EE: Did you have practical labs that involved working with components (either solderless breadboard or actual soldering), or was the entirety of instruction theoretical?


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## Robert (Jul 9, 2022)

I'm no EE, but we had hands on.  Not as much as I would have liked, but it did happen.

We had these big Heathkit training lab things that were connected to a PC as well.   There was a room full of them for the various technologies / subjects.


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## benny_profane (Jul 9, 2022)

Is that Protoboard v2?

When I worked as a tech writer, the number of EEs—regardless of generation or level of education—that actually had practical instruction was surprisingly low.


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## Big Monk (Jul 9, 2022)

benny_profane said:


> Serious question for folks that studied EE: Did you have practical labs that involved working with components (either solderless breadboard or actual soldering), or was the entirety of instruction theoretical?



The first 2 years of most 4 year degrees is heavy on physics and calculus. Since computer systems engineering and electrical engineering are kissing cousins now academically, you also have basic coding courses and labs associated with that. There are also materials courses, which has a corresponding lab as well. 

When I transferred to my second school to finish the last 2 years of my BE, we had circuits, fields and waves and electro mechanics, all of which had labs associated. I also took more involved digital logic courses which had a practical labs as well. 

Especially in electric circuits, we did TONS of breadboarding. It was basically like kids playing with Legos, with large bins of all values of resistors, caps, diodes, etc. Fields and waves was a great lab as well, as we got to use more involved equipment.


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## Robert (Jul 9, 2022)

When I worked on the base that's how it was...   None of the engineers had a clue what they were doing.

They could have probably spouted off some nice formulas back in their prime, but can't figure out how to connect their phones to WiFi now.


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## giovanni (Jul 9, 2022)

benny_profane said:


> Serious question for folks that studied EE: Did you have practical labs that involved working with components (either solderless breadboard or actual soldering), or was the entirety of instruction theoretical?


Not really, they didn't do that in Italy at all. I did have an internship right before I graduated which was cool, but also not a lot of hands on experience (I was working on near field measurements for a radar antenna so it was all coding). I learned to solder a few years later when a friend introduced me to pedal building.


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## Robert (Jul 9, 2022)

benny_profane said:


> Is that Protoboard v2?



If someone can find me a reliable source for these spring contacts we'll have some real fun.

Adafruit used to have them but have since discontinued them.


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## giovanni (Jul 9, 2022)

Robert said:


> When I worked on the base that's how it was...   None of the engineers had a clue what they were doing.
> 
> They could have probably spouted off some nice formulas back in their prime, but can't figure out how to connect their phones to WiFi now.


I can connect to wifi! It's the cable with the roundy plug right?


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## Coda (Jul 9, 2022)

Big Monk said:


> The first 2 years of most 4 year degrees is heavy on physics and calculus.


 
I love physics. As a kid, I always loved science. But as the science became more complicated, and math dependent, I wasn’t able to keep up. I have a fundamental mathematical reason malfunction. I never learned the multiplication table passed 6, and was once told in 4th grade than I couldn't return to my seat until I solved the division problem in the board…I stood there for an hour or so…until it was time for lunch…

When I was in college I took a Fundamentals of Physics course. It was 102, which was the good stuff: electrics, lenses, magnets…none of that fulcrum/lever/physical science bullshit. I ran that class. I could tell you the whole history of Faraday and Kelvin, and explain in detail how Einstein’s relativity theories worked, as well as the history of how they were developed. When it came time to prove it all with math, I tanked…

A decade and one MA in History later, now I’M the Professor…but don’t ask me to explain my grading rubric…


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## Robert (Jul 9, 2022)

I like math but I'm not very good at it anymore because I never use anything but the basics and ohms law.

A couple years ago I hunted down and bought all of the books that would have been involved in an electronics course so I could refresh myself on my own time, no deadlines, no teachers breathing down my neck, no idiot classmates...

I flipped through a Calculus book, nope, back up some.   College Algebra.... nope.. back up some more.

At some point I was finding least common denominators and realized how far I had regressed....    I think it's _more_ frustrating to look at this stuff and know that I used to be able to work it out.


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## MichaelW (Jul 9, 2022)

I suck at all the above, which is why I started this thread, just tell me where to turn the little blue thingies........


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## Robert (Jul 9, 2022)

I turn them until it sounds good, every time.   Seriously.

Ain't nobody got time for none of this "calibration" business.


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## spi (Jul 9, 2022)

benny_profane said:


> Serious question for folks that studied EE: Did you have practical labs that involved working with components (either solderless breadboard or actual soldering), or was the entirety of instruction theoretical?


Yes, in college we did breadboard some circuits, including an 8 bit microprocessor.  That was a spaghetti mess but it worked.  Makes debugging a pedal trivial in comparison.

I learned soldering in a HS electronic shop class, and in that class we built a working multimeter kit.


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