Sunflower Fuzz - Clean and Bias Trimpots

[chongmagic]

I understand that the clean does exactly what it is labeled. Cleans up the fuzz level.

However, for the bias trimpot. I read on the Analogman site that the sweetspot is around 5v. Also the sundial and bias pots are in series it seems so they are basically redundant and perform the same function?

 

[zgrav]

good question. I don't understand why there would be two trim pots in series in the circuit diagram. I would have thought there would be a trip pot for each transistor.

 

[tcpoint]

Germanium transistors are extremely heat sensitive. Just putting your thumb on the transistor will change the HFE reading. In the Sunface, you can dial in the bias at room temperature with the internal bias pot. Then depending on the temperature of where you're playing or how long you're playing, you can adjust the sundial to compensate. Also, you can tweak the sundial to get a more compressed sound or a more open sound, depending on your preference.

 

[Robert]

good question. I don't understand why there would be two trim pots in series in the circuit diagram.

Only one is a trim pot. The other is an external Bias control.

The idea is that you would set the external Bias control to noon and adjust the internal trimpot to the "sweet spot"... then you have variation on either side of the "ideal" bias point with the external control.

Alternatively, this also allows you to install a jumper in the place of the External control if you want a traditional two-knob fuzz, without losing the ability to tweak the bias internally.

 

[zgrav]

Got it. At first I thought the 2 trim pots on the PCB were the ones being discussed. I like the idea of having the bias adjustment as an external pot to change the compression from Q2.

 

[chongmagic]

Gotcha, thank you for clearing that up!

 

[zgrav]

btw -- SUNDIAL is a great name for that external trim pot. given the location right by the board wiring, make sure the bottom of the pot is insulated and the wires attached to the board cannot short out against the posts on the Sundial pot.

 

[piapium]

the problem is when I set the sundial at noon, it is impossible to get less than 7v-6v though I set the trimpot at minimum. There is a problem and need help.

 

[Chuck D. Bones]

Post on the troubleshooting forum please. Include photos and the usual info.