Sandspur / Sunflower questions.

[Duffman]

Hi i have two small questions regarding the sandspur/sunflower:
- What is the point of the R3 (1k) resistor? I haven't seen this in the original pedal, nor most other fuzz-faces. Is it to buff up the signal because the sundial is only 5k? I plan on bypassing this with a jumper-cable and using a 10k sundial.
- R4 is a 470-Ohm resistor; I notice the original one uses 390 ohm for Si and 680 ohm for Ge. I think most calculators give a 220 ohm value for building the fuzz face. Any reason to go for one or the other? I was reading that this can make your sound darker or higher, i guess one would change the value to remain as 'clean' as tone wise possible. Any ways to calculate which one you need?

Thanks in advance!

 

[pbliven]

Yeah I'm not sure why R3 is there either. I did a sunflower build using this schematic of the Analogman Sunface I found on Greybench Electronics' youtube channel. It sounds great! I did have to switch out transistors a bit, because of the noise in some of them. Because of this I suggest getting some transistor sockets so you can easily switch out transistors instead of what I had to do, un-soldering and re-soldering them.

 

[Coda]

I believe R3 is there to keep the Sundial usable at the extremes…

 

[manfesto]

R3 is a limiting resistor to ensure that the bias resistance never goes below 1K (like what would happen if you accidentally turned both the bias and sundial controls all the way down to zero). Its presence is just insurance and it doesn't hurt to leave it in the circuit, at *worst* it's the difference between your bias trimpot being set at, say, 4K instead of 5K, but you should still be able to hit your expected bias voltage, and once it's set, your sundial will still have the same range.

As for the 470 ohm resistor, it helps set the output level and gain of the second transistor, read the Electrosmash article under "Voltage Total Gain" for all the fun math (for their schematic, R2 is the 470 ohm resistor, and R3 is the total resistance of the 1K, bias, and sundial controls)

ElectroSmash - Fuzz Face Analysis

The Fuzz Face is a distortion guitar pedal designed in London by Arbitrer Electronics Ltd in the autumn of 1966. This analysis covers the first Arbitrer Fuzz Face model equipped with PNP germanium transistors from the first releases.

www.electrosmash.com