Since Fairchild finally discontinued the 2N5457 JFET along with a number of other JFETS in the TO92 package, prices have been rising and tales of fakes have been increasing on audio and stomp-box forums. You can still buy the 2N5457 from Central Semiconductor, but they are very expensive – too expensive for Stompville to consider buying sufficient quantities to match them up into pairs and quads.
Fairchild/OnSemi 2N5457’s are available on the surplus market, but one of the problems with surplus suppliers is that (irrespective of whether the parts are genuine or fakes) you have no guarantee that ESD handling precautions have been observed so it’s difficult to buy with any kind of confidence.
Neither NXP nor OnSemi do TO92 JFETs any more and the only TO-92 low-noise audio JFET that Fairchild still supply in a TO-92 package is the PF5102 (update – the PF5102 is discontinued as well). The remaining Fairchild TO-92 N-channel line up comprises the J111, J112 and J113, although these parts are not marketed as low-noise items. The question is, can we substitute the 2N5457 without adjusting other component values? The answer varies from maybe through probably to absolutely, depending on the requirements of the circuit.
Regarding absolute maximum ratings and thermal characteristics, the 2N5457 is fairly modestly specified so the PF5102, J112 and J113 are as-good-as or better in all areas.
The two most important basic electrical characteristics for substituting and matching JFETs are Vgs(off) and Idss.
From the Stompville matching archive, typical samples of 2N5457 have an Idss between 2.5 and 4.0 mA with the peak between 3.0 and 3.5 mA. Corresponding Vgs(off) range is -1.6 to -2.0 V.
Stompville samples of 2N5457 with Idss between 4 and 5 mA have a cutoff voltage a little under -2.0 V. Whereas
Stompville samples of PF5102 with Idss between 4 and 5 mA have a cutoff voltage of about -0.85 V.
Although the Vgs(off) values for the J113 look comparable to the 2N5457 and the Idss is specified as 2.0 mA minimum, in practice, we find that the average Idss is about 20mA with a range between 10 and 23 mA.
We don’t have any data for the J112, but the Idss will be even higher than the J113.
So, where does this leave us? Well, we could consider substituting a low-Idss PF5102 for a 2N5457 in any circuit design. We could possibly substitute a J112 or J113 for a 2N5457 provided our circuit is immune to the Idss difference.