JFET availability - adapting to the circumstances

[Grubb]

Recently I've been messing around with the HM2 circuit and throwing around different design ideas. During that process, I've noticed that the stock of common SMD JFETs is seriously dwindling in the usual places I look. I know someone somewhere will have a stash of them - getting my hands on a few here and there is not a big concern. I think the thing I'm wondering about is what we do when that supply is used up. How do DIY pedal builders and designers intentionally work around the current limited availability of parts that are featured in many popular designs?

For the HM2, the 2N5457s used in the in/out buffers are virtually gone, and the MMBF5457s are in minimal supply. MMBFJ201s would be an OK sub, but they are in serious backorder in most places. Where they are available, some of them now cost $3 each. Where do we go from here? Is it time we revised some of our designs to utilise IC-based buffers instead of JFETs? What do we do for transistor-based drive circuits? I'd love to hear what others are thinking about this.

 

[Betty Wont]

2N5457 N-Channel JFET - PedalPCB.com

N-Channel JFET

www.pedalpcb.com

MMBF5457 JFET (SMD) - PedalPCB.com

SMD JFET (5 pcs)

www.pedalpcb.com

The sky is falling!!!

 

[owlexifry]

Is it time we revised some of our designs to utilise IC-based buffers instead of JFETs?

this would be pretty cool tbh

 

[Grubb]

If we look at parts availability data, we know that these parts exist in far smaller quantities than they have in the past. The reason I started thinking about this at all is this graph of MMBFJ201s from last year:


The MMBFJ201s haven't been discontinued yet and are occasionally restocked. They still have very low availability from authorised distributors this year, with some periods of no availability. The factory lead time on them at Mouser is 158 weeks. Here's a more up-to-date graph:


All 2000 or so of the MMBF5457s still with authorised distributors are with Flip Electronics, a specialist supplier of EOL parts. They won't be providing them for general consumption.


As I said in my original post, none of this means you can't get your hands on some parts for now. Pointing out where you can find some in the meantime doesn't really address the question. Coming up with other ways to preserve our designs that don't rely on dwindling parts availability and spiking prices is a smart thing to do because eventually, we are going to need to adapt them.

this would be pretty cool tbh

Maybe! I was reading a post by RG Keen on a related topic that was talking about how ICs often reproduce audio in a higher fidelity way and don't provide our ears with the buttery harmonic distortion we enjoy from JFETs and the like. In some designs, the more objectively faithful and accurate IC reproduction of your guitar's sound could be less subjectively pleasant. But when ICs cost less than some transistors and are available in vast quantities, we should think about designing or building with them where we can.

 

[szukalski]

You have some good points there. JFETs as we know them are getting rarer, even if we use them in relatively small amounts. I think part of this is that JFETs have moved on, but we're still using the legacy models because this is what we have known and learnt.

I do like ICs as buffers and boosts, the transparency is great, but once they clip it gets uncomfortable for my ears. I am all for replacing transistors with ICs where-ever possible.

 

[coltonius]

I’m curious, though, how much of this is due to the pandemic and supply chain-related issues that are still being ironed out. Remember it wasn’t too long ago (and may still be continuing) that the auto industry was brought to its knees by a shortage of semiconductors used in new production vehicles.

That may be an optimistic perspective, it may also be naive of me to hope the Chips Act of 2022 will assist in future availability. Either way, I am skeptical that the data presented represents the future of JFETs; if you zoom in close enough to any graph, you can make it look as good/bad as you want.

 

[Grubb]

I’m curious, though, how much of this is due to the pandemic and supply chain-related issues that are still being ironed out.

With the MMBFJ201, that's almost certainly the main driver of availability at the moment. A lot of manufacturers still have a backlog to work through from that period of time. The MMBF5457 is a different kettle of fish, once we use up whatever finite stockpiles we have, those are gone. I should probably buy a bunch of them while I still can.

Either way, I am skeptical that the data presented represents the future of JFETs

It's good to be skeptical, that's my default setting too The data represents the recent availability of two JFETs that are commonly used in pedal circuits. Whether or not that pattern continues for MMBFJ201s into the future is an open question. At the very least we can say confidently that there is a relative shortage of these parts at this point in time. If it continues to be this way, the logical implication would be that it ends with supply issues that affect us. Adapting to parts becoming unobtainable by finding suitable substitutions or workarounds is what builders and designers did in the past, and I expect we will have to do it again in the future.

if you zoom in close enough to any graph, you can make it look as good/bad as you want.

Quite right. I got this data from Octopart and presented it here as it was presented on their page. The way they have chosen to present the data could definitely influence the way people interpret it.

 

[jimilee]

Snatch them up when you find a good deal. Barry has sales on them all the time.

 

[temol]

I don't think there's much we can do other than stock up whenever possible. I'm not complaining yet, but in two or three years, who knows... I don't like the prospect of switching to ICs, but I'm also not going to overpay as you often have to for germanium transistors now.

 

[music6000]

I don't think there's much we can do other than stock up whenever possible. I'm not complaining yet, but in two or three years, who knows... I don't like the prospect of switching to ICs, but I'm also not going to overpay as you often have to for germanium transistors now.

It equates to finding someone off the map that still has NOS old stock that is not wanting an arm & leg for it.
There are still thousands of 2N5457 & j201's thru hole transistors available but at a price.
I have someone local that is off the map in electronic repair but he has a lot of stock (no 2N5457 or J201's now) from 40 years ago that is for sale for the around the same price it was back then. I always give him double what he charges & I'm still km's in front, No astronomical shipping charges!

Is there an russian Transistor that is equivalent to J201's, I haven't had to go down that path yet!?

 

[temol]

Is there an russian Transistor that is equivalent to J201's, I haven't had to go down that path yet!?

From what I remember it's KP303A (КП303А)

 

[Cabintech]

Looks like the SMT format of the J201 will be around for a long while. DigiKey has 22,000 in stock, Mouser has 150,000+ on order. Does not seem like a component going out of production. For through-hole use there are plenty of J201-on-SMT adapters around for less than $1.50. You can have one slapped on your assembled PCB for less than $0.20 in quantity at JLCPCB. I would be very suspect of data from Octopart, making things look scarce helps their business model.