Biasing jfets Super '64
- Thread starter Trevlett
- Start date
Typically for jfet overdrive circuit, you want to bias the Dound half the supply voltage. Since this pedal has the charge pump to run at 18v, you can target 9v. Or to be more precise, you could measure the voltage at D102 cathode, which should be slightly under 18v, and take half of that.
The Superbolt is very similar to the ROG Supreaux circuit, which runs at 9v, and ROG recommends biasing that to 4.5v. I also checked the comments from the tagboard effects post for the superbolt, and they recommend 9v (or half the supply after the diodes).
The half supply on drain rule isn’t always followed, for example the ROG Supreaux Deux runs at 18v and they recommend biasing at 12v. ROG has an article about the ‘Fetzer Valve’, which is the jfet approximation of a tube, which is the basis for several ROG designs, and there’s a section in that article that goes more in depth about biasing. So for this build I’d recommend 9v based on the recommendations of others, but you can also experiment with 12v or somewhere in between.
The Superbolt is very similar to the ROG Supreaux circuit, which runs at 9v, and ROG recommends biasing that to 4.5v. I also checked the comments from the tagboard effects post for the superbolt, and they recommend 9v (or half the supply after the diodes).
The half supply on drain rule isn’t always followed, for example the ROG Supreaux Deux runs at 18v and they recommend biasing at 12v. ROG has an article about the ‘Fetzer Valve’, which is the jfet approximation of a tube, which is the basis for several ROG designs, and there’s a section in that article that goes more in depth about biasing. So for this build I’d recommend 9v based on the recommendations of others, but you can also experiment with 12v or somewhere in between.
