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08-22-2019, 02:39 PM
Hi
Jfet Idss is not important for switching unless the signal currents can be significant, i.e. all the circuit impedances are very low, none of which is the case in a tube amp.
Rds-on is the key figure of merit for jfets as audio mutes. In the late 1980s I used the 2SK30s because the pedal guys used them, but later I realised it is actually far from the ideal audio switch. It has a very low Vgs so goes from looking like an infinite resistance down to its lowest resistance with very little gate voltage, which is ideal when the supply voltage is effectively half of a 9V battery. Rds for the 2SK30 is about 400R, which is okay in a tube amp where series resistances are in kilohms or tens of kilohms.
The best jfets for switching are the National Semiconductor series from J105 to J112. These have a lower Vds rating than the 2SK30 but there on-resistance is <100R for the high-end of the series and as low as a few ohms at the other end.
Jfet Idss is not important for switching unless the signal currents can be significant, i.e. all the circuit impedances are very low, none of which is the case in a tube amp.
Rds-on is the key figure of merit for jfets as audio mutes. In the late 1980s I used the 2SK30s because the pedal guys used them, but later I realised it is actually far from the ideal audio switch. It has a very low Vgs so goes from looking like an infinite resistance down to its lowest resistance with very little gate voltage, which is ideal when the supply voltage is effectively half of a 9V battery. Rds for the 2SK30 is about 400R, which is okay in a tube amp where series resistances are in kilohms or tens of kilohms.
The best jfets for switching are the National Semiconductor series from J105 to J112. These have a lower Vds rating than the 2SK30 but there on-resistance is <100R for the high-end of the series and as low as a few ohms at the other end.
