SandSpur Fuzz biasing?

[MichaelW]

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!

 

[Big Monk]

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.

 

[Coda]

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…

 

[Big Monk]

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.

 

[Coda]

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…

 

[Big Monk]

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".

 

[MichaelW]

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.

 

[Big Monk]

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.

 

[Coda]

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

 

[MichaelW]

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.

 

[Big Monk]

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.

 

[Big Monk]

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?

 

[Big Monk]

No, been too busy building memory men and electric mistresses

True, true! You right!

 

[Coda]

No, been too busy building memory men and electric mistresses

Drag…

 

[Coda]

Someone had to leave the kids table and build real pedals

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

 

[Big Monk]

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...

 

[Coda]

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

 

[Robert]

Someone had to leave the kids table and build real pedals

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..

 

[HamishR]

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??

 

[giovanni]

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…