J201 and 2N5457 for buffers and pedals

[GeorgeG]

J201 and 2N5457's are used frequently in all sorts of popular buffer stages and distortion pedals. It seems that the 5457 is virtually extinct and the only reliable source for J201's is at Mouser and they are over $3 a piece. Given that you need to sort through a pile to get the sets needed for some projects that's a stiff premium. What are you guys doing for JFET's in these designs?

Thanks,

George

[smallbearelec]

For a TO-92 part that is workable for many apps, try the Fairchild J112 or PF5102:
http://www.smallbear-electronics.mybigcommerce.com/transistor-fet-j112-fairchild/
http://www.smallbear-electronics.mybigcommerce.com/fairchild-pf5102/

If you can use the J201 with a relatively low transconductance, I have these:
http://www.smallbear-electronics.mybigcommerce.com/transistor-fet-j201-generic/

You can also go SMD, with TO-92 adapters if you want:
http://www.smallbear-electronics.mybigcommerce.com/fairchild-on-semi-jfet-mmbfj201/
http://www.smallbear-electronics.mybigcommerce.com/fairchild-jfet-mmbf5457/
http://www.smallbear-electronics.mybigcommerce.com/sot-23-to-to-92-surfboards/

[Ark Angel HFB]

It seems that the 5457 is virtually extinct...

|

https://www.taydaelectronics.com/mmbf5457-jfet-n-channel-amplifier-transistor-sot-23.html

[reddesert]

Different JFET projects have different needs.

For a gain-of-1 buffer several types of JFETs will do; you don't need a J201 / 2N5457 in particular, usually, just something that can operate from a 9V supply with headroom.

For a gain-stage or distortion stage like in a number of amp emulator pedals (many derived from the Runoffgroove Fetzer Valve idea), the drain and source resistors have to be adjusted to bias the drain voltage of the JFET to a useful operating point (ie somewhere in the middle of the supply voltage, typically 9V), and the ratio of Rdrain/Rsource sets the stage gain. J201's have a small Vpinch, and the effect of this is that they can be set up for higher gain. See the Fetzer Valve page http://runoffgroove.com/fetzervalve.html for more details. The effect of this long story is that for such a pedal, if it asks for a J201 or 2N5457, you really do need a FET with Vp in the correct range. You don't have to match the JFETs though.

For phasers where the JFET is used as a variable resistor, like the Phase 90, you do need to match the JFETs in Vp to operate at the same point, so there you need a larger set of JFETs to match from. It is said that the SMD JFETs are more consistent and so easier to match.

[amz-fx]

Mouser has the J112 in through-hole for less than 50 cents each that will work for buffers and many amplifier circuits. They also have the BF256B in through-hole for about the same price and it is a good general purpose device, though you should check the pin configuration on the datasheet before placing it on the pcb.

Best regards, Jack

[cnspedalbuilder]

Don't be afraid of the SMD J201s! With a TO-92 adapter it's pretty straightforward.

Guitarpcb.com had a special deal with SMD j201s pre-soldered onto adapters, but it looks like those are unavailable at least for now. If you look on OSHpark, you can find several J201 adapter boards for very cheap, and the pinouts should line up with the TO-92s. There are many sources for the SMD J201s and standard 5457s including smallbear.

[Prehistoricman]

I bought J113s for modding my Digitech XP100 but I also built the Uno from runoffgroove with the ones I had spare and they worked just fine (sounds the same as J202s to my ear, only needing different values for biasing). Now the J113 is marked on the datasheet as being a switching JFET but I don't think this really means much given my experience with them.

Edit:
It's worth noting that J113s are a lot gainier than the J201s that are specified in the Uno schematic. I had to remove 2 or 3 of the source capacitors to get a sensible amount of gain.