J201 and 2n5457 replacements

[bsas]

Hi all!

It is getting hard to find those. Sorry for the noob question, but which other FET we can easily find that can replace them?

Thanks!

[Beaker]

In short, there aren't any.

It may be possible to replace them with other JFETs, but only on a few circuits - most pedals that require these JFETS don't really work very well with replacements. (I think I read somewhere that J230 work in some builds that spec J201).

When you take into account the amount of fake 2N5457 and J201 transistors that you will come across - especially from Chinese ebay sellers, we are in a bit of a bind.

We have had guys on here already, having all kinds of problems with JFET builds - problems that they should not really be experiencing, or should be easy to cure. The problems result from the fact that they have bought a batch of fakes, and they don't realise it. It's only when they have swapped the fake parts for genuine ones, the problems resolve themselves.

The good news is that you can buy surface mount JFETS and tiny PCB adapter boards that you can use in their place - although they are not widely available. Hopefully someone will reply with a source for these.

I have found places to get 1000, but not 10 or 20!

[Muadzin]

I get my SMD JFET's and adapterboards from www.diyguitarpedals.com.au. I thought I was using real J201's from Polida until I switched them for these SMD JFET's and suddenly entire pedals came to life.
I usually order them in batches of 25. Most of them J201's although I have ordered MMBF5457's and some MMBF4393's as well. Although I think currently he's out of adapter boards as I can no longer find the option to include an adapter board.

[tabbycat]

a word from our leader on the subject:

"They're both JFETs so you could go for 2N5457, 2N5458, 2N5459, 2N5484, 2N5485, 2N5486, MPF102. These all have the same DSG configuration as the J201 but would have to be turned 180º if used as replacements for the 2N5952 (GSD).

You could also use something like the 2SK117 or 2SK170 but they are both DGS so you would have to alter the scheme to reflect that."

http://www.freestompboxes.org/viewtopic.php?f=51&t=4791#p53346

rg keen is a guru and worth considering his opinions on jfet substitutions too:

"JFETs present a bigger problem. N-channel JFETs vary all over the map, and by an almost intractably large amount. The big problem is that the variation of Vgs and gm values is huge for these parts. This is one place that you may have real problems. However, almost all JFET circuits are set up with trimmer resistors to adjust the operating conditions for the JFET because of the large variation in the JFET. I personally stock 2N5485 and 2N5457 JFETs. BF244C is almost exactly the same as the 2N5485."

from 'keen's laws' on part substitutions http://www.geofex.com/effxfaq/keenslaws.htm

also worth checking rg's comments in this diysb thread re jfet substitutions:

http://www.diystompboxes.com/smfforum/index.php?topic=86903.0

[bsas]

Looks like the SMD solution is the most reliable, am I right?

Found a bunch of those adapter boards in OSH Park:
https://oshpark.com/shared_projects/G5s4j1KC

I think I will order a couple since they are quite cheap (like, 50 is around $8) and a bunch of SMD J201 and 2n5457 to try out.

Do you guys have any suggestion on tricks to solder SMD since I never did it?

Thanks!

[tabbycat]

Beaker wrote

The good news is that you can buy surface mount JFETS and tiny PCB adapter boards that you can use in their place - although they are not widely available. Hopefully someone will reply with a source for these.

I have found places to get 1000, but not 10 or 20!

Muadzin wrote

I usually order them in batches of 25. Most of them J201's although I have ordered MMBF5457's and some MMBF4393's as well. Although I think currently he's out of adapter boards as I can no longer find the option to include an adapter board.

maybe the time to take matters into our own hands re smd 201 and adapter boards is nigh?

if all interested parties could commit to a given amount at a given price perhaps we approach a small run manufacturer. not sure if this is an oh park thing but it's a basic board. anyway, an idea.

[bsas]

Are you suggesting us to get together and order the board + the SMD already soldered using pick-and-place machines?

That would be very cool. We could design the "smallest" board possible and order a big bach of MMBF5457 and MMBFJ201. Those you can buy in 3000+ reels original from Fairchild.

I don't know how much it would be to request to manufacture like 3000x 5457s and 3000x J201s.

Also, it would be cool (but I don't know if it is feasible) if the P&P could already solder the leads :D

[Beaker]

These daughter boards are for SOT-23 surface mounts, which are the largest form of surface mounts, and are supposed to be pretty easy to solder - though I've never tried them myself yet.

[bsas]

Another question related to FETs:

I just did the matcher circuit:
http://tagboardeffects.blogspot.co.uk/2012/07/greatly-improved-jfet-matcher.html

So, here is my questions:

1) Can this circuit be used with MOSFETs? (example: 2n7000)?
2) What is the expected values in a J201? I just want to be sure the ones I got on eBay are not that bad, and I want to in the future measure the SMD ones.

Thanks!

[Frank_NH]

Great that you built a JFET tester/matcher.  The most important parameters associated with any JFET are the idle current (Idss) and the "pinch-off" voltage (Vp) that you measure with this device.  The stage gain and required biasing are directly tied to them.  

To answer your questions:

1) Can this circuit be used with MOSFETs? (example: 2n7000)?

No.  MOSFETs do not work like JFETs.

2) What is the expected values in a J201?

First read this:

http://www.runoffgroove.com/fetzervalve.html

Then look at the bottom of the post.  You'll see "average" values for a variety of JFETs.

Out of ten (10) J201
average Vp: -0.83V (spanning from -0.57 to -0.97)
average Idss: 0.64mA (spanning 0.30mA to 0.83mA)

A couple of additional points:

* There are many substitute JFETs out there if read through the datasheets.  For example, I found an eBay dealer selling J202 for a great price.  J202s are a near drop in replacement for 2N5457s.

* There are two cases where the JFET's Idss, Vp are not as critical so a range of JFETs can be used:
  - JFET buffers (source followers)
  - Mu-amp gain stages such as you see in BSIABII and many others (including the Catalinbread Galileo II shown on the main page).  Again, a range of JFETs can often be substituted

* Do test ALL of your JFETs just to make sure their Idss, Vp fall within the datasheet specs (I have had a bad JFET that didn't meet spec and tossed it).  If you want to get fancy, take some white masking tape and attach it to the leads and mark a label on it (like A1, A2, A3...).  Then log the label and the measured Idss, Vp in a spreadsheet.  When you go to use your JFETs you can pick ones that are close.  An alternative would be to put ones that are "close" in their specs in a bag, then mark the bag with the approximate Idss, Vp for the group.

* You can predict the performance of a JFET common source stage if you want to get into the formulas from JFET theory.  That is for a given JFET, source resistor, and supply voltage, you can determine the required drain resistance and gain.  This allows you to determine the right sized drain trimmer (100K is usually too large) for circuits like Dr. Boogie.  Or you can determine the appropriate JFET Idss, Vp for given source, drain resistors (this is where your measurements and labeling of JFETs come in VERY handy!).  I made a spreadsheet that I shared in a previous post which does this, if you're interested in this sort of thing.

[bsas]

Wow, this article is super interesting!

So, in theory, should I always measure the FET before doing the circuit and then should I replace some of the resistors and the capacitor that bias it?

If so, it is curious that pedal manufacturers cannot do that (of course), and then, even two exact same pedals that uses FET (let's say, 2x OCD in the store) will sound different, am I right?

[bsas]

By the way, yes, I am very interested in your spreadsheet :)

[Frank_NH]

Here's the thread with the spreadsheet...

http://guitar-fx-layouts.42897.x6.nabble.com/JFET-Common-Source-DC-Bias-Spreadsheet-td14316.html

[bsas]

Questions:
- Did anyone already did a pedal that is basically just the Fetzer Valve to hear how it sounds?
- Should I measure the FETs and change the bias resistor on pedals that uses them?

Thanks!

[Frank_NH]

- Did anyone already did a pedal that is basically just the Fetzer Valve to hear how it sounds?

Here's a vero for you.  Should sound like a nice booster with some crunch (depending on your jfet).

Marsha Valve

- Should I measure the FETs and change the bias resistor on pedals that use them?

For pedals where the drain resistor is fixed (such as the original Wampler Plexidrive), yes you should measure the JFETs to see if the fixed drain resistor value is appropriate.  However, most effects that use JFET stages have trimmer pots for the drain resistors to avoid this problem.  You can then stick in any JFET you want and adjust the trimmer to achieve the proper bias at the drain (usually around 1/2 the supply voltage).

[Sensei Tim]

mouser has thru hole J201's from InterFET.  No idea how they sound. they are a bit on the ridiculously priced side, tho:

http://ca.mouser.com/ProductDetail/InterFET/J201/?qs=sGAEpiMZZMvplms98TlKY8skfZQpQP4sTauuqV%252bhBdb8eh7Ae4NdvQ%3d%3d

i use these SMD J201's for all of my builds with adapter boards from oshpark

http://ca.mouser.com/ProductDetail/Fairchild-Semiconductor/MMBFJ201/?qs=sGAEpiMZZMvplms98TlKYyI%252bsdYAyN1NorN9mwzFaJw%3d

Price break happens at 100...   100 JFETs for $20? i'm up for that!

As for how to mount them, i mount the adapter boards onto header pins. Then i put a touch of solder on the center pad. i hold the J201 in my tweezers and push the center pin onto the pad while keeping the solder molten and then once it's in place i remove the iron.  the j201 is now solid and i can solder the other two terminals without worrying about it slipping out of place.

[Sensei Tim]

bsas wrote

That would be very cool. We could design the "smallest" board possible and order a big bach of MMBF5457 and MMBFJ201. Those you can buy in 3000+ reels original from Fairchild.

I don't know how much it would be to request to manufacture like 3000x 5457s and 3000x J201s.

Also, it would be cool (but I don't know if it is feasible) if the P&P could already solder the leads :D

if you go to a board manufacturing house, they'll use solder paste and a reflow oven. much more efficient than soldering the leads manually.

CAD pricing on J201's from mouser


1:  $0.783
10:  $0.461
100:  $0.218
1,000:  $0.162

MouseReel™ Reel Service Fee $8.50 Price will be calculated in cart.
Full Reels of 3000
To purchase full reel, order in multiples of 3000:

3,000: $0.138
9,000: $0.125
24,000: $0.117
45,000: $0.104


so you'd be lookin at $300-400 for a reel of 3000 + cost of the adapter boards + cost of populating them.

[bsas]

Yes, I already bought 100x MMBF5457 and 100x MMBFJ201 and a bunch of OSH park adapters.
I am just curious to see how bad it will be for me to do it since I never solver a SMD :D
Well, there is a first time for everything in life... hehehe

[Muadzin]

If I can do it, anyone can. I dab some solder onto one of the pads, then put a transistor between the tips of a plier (this where you should be careful because they will be a bitch to find if they snap free), reheat the solder on the pad and shove the pin of the transistor into it. After that the transistor is fixed into place and you apply solder to the other two pads/pins. Use the thinnest strand of solder you can find though and it probably still won't win you any solder awards.

Afterwards I always check to see if there is continuity between the transistor pins and the holes where you can solder the legs into.

[Beaker]

That's a good place to start.

It's worth pointing out that OSH Park is far from the cheapest way to do this.

They are great, if you only want a few PCBs manufacturing. However there are dozens of PCB fab houses in China (many of them list on ebay) that will make 3000 PCBs (to go with a reel of 3000 JFETS - or indeed 6000 for a reel each of SMD J201s and SMD 2N5457), at a much cheaper price.

I like the idea of getting the PCBs supplied with the SMDs already soldered in place, though I don't know if the PCB suppliers would be able to do this, or whether they would need to sub-contract them out to someone else to have it done. It also remains to be seen if that would hike the price up to the point that it would make it un-economical.

If we could get one of our PCB design experts like Chris6061 or Freppo to draw up a PCB for this, (that they would allow us to use), it might be possible for us to organise a group buy, depending on interest of course.

I would hate to see someone take the reins on this, order 3000 of each, and end up only getting orders for a few hundred!