How to determine jfet source bypass capacitor voltage rating?

[substitute]

I've breadboarded the ol tapeop jfet hampton circuit, it's working fine and sounds excellent. The 470uf bypass cap's voltage rating isn't specified in the schematic . Is there a rule of thumb for determining this value? The parts I'm using on my breadboard version are over speced and physically much larger than I'd hope to use in the final build.

Thanks

 

[PRR]

Build without that cap. Measure voltage there.

You could also figure: hardly any JFET source wants to be over 5V, and hardly any e-cap is under 5V.

 

[substitute]

Thank you PRR, always happy to hear from you.

 

[john12ax7]

Another approach is you could view the jfet as a variable resistor,  worst case is a drain to source short.  Then you can calculate a voltage divider with the supply and all associated resistors.  Add at least 50% margin and then you have a starting point.

Of course always best to measure and verify.

 

[Khron]

Worst-worst case, and with a huge margin left, you can go with the circuit's supply voltage as a rating.

Way overkill, of course, but you can definitely be sure that way

 

[JohnRoberts]

Worst-worst case, and with a huge margin left, you can go with the circuit's supply voltage as a rating.

Way overkill, of course, but you can definitely be sure that way

+1

JR

 

[OneRoomStudio]

If you're using a 24V supply and a 1K82 source resistor like in the original, there is 1.09V across the source resistor according to SPICE.

 

[substitute]

Wow, only ~1v. The footprint for 25v or 10v Panasonic caps is the same so I think I’ll just get the 25v which will cover the supply voltage.