Hello folks, i have around 100 fake to92 J201 jfets. While i was sorting out my parts bin, i thought i should drop a question about how can i make use of them. Even they are fake maybe i can match them to make phase90? Or i can use them as input and output buffers in circuits? Also i got some fake 2N5457's , around 30 of them. I didn't have time to measure them to see how " out of spec they are". Or maybe i can use them for jfet type of switching purposes?
Have a great day/night for you all!
out of curiosity, are these fakes marked with any brandnames or logos [if yes, pictures please], or just anonymously laser etched? what about them leads you to say counterfeit?
Quote from: duck_arse on December 18, 2018, 08:55:39 AM
out of curiosity, are these fakes marked with any brandnames or logos [if yes, pictures please], or just anonymously laser etched? what about them leads you to say counterfeit?
Yes , they have brand markings on them ( see the picture ) , TO-92 J201's out of production, only smd version available and i tested them out, 10 of them, all out of spec. About 2N5457's , i don't remember measuring them but, as far as i know they are out of production too, then i have time, i will measure them all and put it in some excel sheet, so we all can see the average values. Also i have smd versions of both and i just switched them in a circuit, fake ones didn't work, smd ones were bang on!
(https://i.postimg.cc/Q9Tr3Vqx/IMG-20181218-165836.jpg) (https://postimg.cc/Q9Tr3Vqx)
I have a bunch of probably fake JFET transistors, but I measure them and sort, so I can find usable ones for different roles.
I've seen interesting jewelry, earrings made with electronic parts.
dave
Quote from: davent on December 18, 2018, 11:33:49 AM
I've seen interesting jewelry, earrings made with electronic parts.
dave
Maybe I should use them for necklades for my gf, perfect combination with her diode wristband :)
Quote from: abakuzam on December 18, 2018, 11:39:58 AM
Quote from: davent on December 18, 2018, 11:33:49 AM
I've seen interesting jewelry, earrings made with electronic parts.
dave
Maybe I should use them for necklades for my gf, perfect combination with her diode wristband :)
My wife has various pieces made with electronic bit and pieces.
dave
Couple of years back, I had 2 fake 201's. At least I think they were fake. I'd tried one in a Mayqueen and they didn't work until I use a 20x trimmer to bias them (by ear) and even then the sweet spot was within about 1/4 turn. I ended up with a great sounding pedal with so much bass that only some amps can handle it. I posted about it here at the time.
Just mentioning it to confirm that if you polish a turd enough, it can end up being quite shiney
QuoteWhile i was sorting out my parts bin, i thought i should drop a question about how can i make use of them. Even they are fake maybe i can match them to make phase90?
It depends is they are plastic with legs, remarked BJTs, or out of spec JFETs. Matching the JFETs should work OK. It's not as if JFETs are precise in the first place. You'd probably want to characterize a few to see what they really are in terms of parameters.
QuoteMy wife has various pieces made with electronic bit and pieces.
dave
Wife: "What matches this top better? the 2k2 necklace or the 4k7 necklace."
Quote from: stallik on December 18, 2018, 03:13:31 PM
Couple of years back, I had 2 fake 201's. At least I think they were fake. I'd tried one in a Mayqueen and they didn't work until I use a 20x trimmer to bias them (by ear) and even then the sweet spot was within about 1/4 turn. I ended up with a great sounding pedal with so much bass that only some amps can handle it. I posted about it here at the time.
Just mentioning it to confirm that if you polish a turd enough, it can end up being quite shiney
Well since i have a lot of that turd, it may produce something nice. I will build a test circuit, ROG Uno maybe, and test them out, that should give me the flexibility
Quote from: Rob Strand on December 18, 2018, 03:15:50 PM
QuoteWhile i was sorting out my parts bin, i thought i should drop a question about how can i make use of them. Even they are fake maybe i can match them to make phase90?
It depends is they are plastic with legs, remarked BJTs, or out of spec JFETs. Matching the JFETs should work OK. It's not as if JFETs are precise in the first place. You'd probably want to characterize a few to see what they really are in terms of parameters.
They are out of spec jfets, i was able to confirm that, they are jfets. I will measure them and post my results in here. I remember that i built a okko diablo back in the day with them, it sounded okay to my untrained ears, maybe there is hope!
QuoteThey are out of spec jfets, i was able to confirm that, they are jfets
Probably usable. Especially for controlled resistors.
Those that I have are really out of specs, for example, Vgs(off) is in margins for 2N5457, while Idss is corresponding to 2N5458. But I use them for different stuff and they work fine.
I measured 36 of the J201 jfets, can't find the rest of them , probably, under my bed ahah :D
i measured vgsoff with this : https://www.rullywow.com/jfet-matcher-project-vgsoff/
Idss with this : http://stompville.co.uk/?p=112
I used same 9v regulated power supply , these are my results:
Note: i didn't bother to put -0,xxx type of measurement for vgsoff, you can put -0, at the begining of the numbers.
Vgsoff values seems to in spec but Idss values are waay out of specsi checked my smd j201's (mmbfj201) they all seem to be in specs.
VGS(off)
Volts Idss mA
488 1,54
522 1,15
668 1,23
424 1,23
442 1,73
460 1,42
620 1,19
698 1,51
696 1,52
618 1,24
448 1,58
406 1,3
600 1,65
452 1,45
610 1,12
625 1,31
450 1,41
485 1,16
460 1,15
436 1,64
747 1,01
637 1,76
765 1,13
424 1,17
443 1,02
589 1,07
374 1,11
585 1,51
512 1,19
451 1,18
753 1,48
365 1,82
526 1,14
490 1,3
638 1,47
Make em into diodes. Connect D+S together. Unique low gain tubey clipping similar to, but not the same as using rectifier diodes for clipping. Worth a go!
Quote from: PariahBrothermann on December 19, 2018, 08:06:32 AM
Make em into diodes. Connect D+S together. Unique low gain tubey clipping similar to, but not the same as using rectifier diodes for clipping. Worth a go!
That's good idea , sounds interesting , thank you!
No worries. You get a low gain od which is pretty responsive. It's my plan for the 100s of fake jfets I have. If you use a combination of fet and diode clipping, things can get pretty interesting... Good luck :D
Quote from: PariahBrothermann on December 19, 2018, 08:11:46 AM
No worries. You get a low gain od which is pretty responsive. It's my plan for the 100s of fake jfets I have. If you use a combination of fet and diode clipping, things can get pretty interesting... Good luck :D
Got any suggestions about which circuit i should try? i was thinking about replacing them in zendrive type of circuit, instead of 2n7000 , j201 could put some interesting results
Zendrive sounds like a fun option... I'd suggest socketting the diodes and experimenting with different combinations. That way you can check you like it with the fets, try different diode combinations, and find the grail!
Quote from: abakuzam on December 19, 2018, 08:00:40 AM
Vgsoff values seems to in spec but Idss values are waay out of specsi checked my smd j201's (mmbfj201) they all seem to be in specs.
If you put those values into JFET calculator on ROG, you will see that they are pretty usable for Fetzer Valve and similar circuits. Maybe out of specs, but actually really usable.
Quote from: rankot on December 19, 2018, 04:25:48 PM
Quote from: abakuzam on December 19, 2018, 08:00:40 AM
Vgsoff values seems to in spec but Idss values are waay out of specsi checked my smd j201's (mmbfj201) they all seem to be in specs.
If you put those values into JFET calculator on ROG, you will see that they are pretty usable for Fetzer Valve and similar circuits. Maybe out of specs, but actually really usable.
I appreciate it a lot, actually, i was reading that article today, so many information to learn and apply, then fail, try to debug, and learn more! That's one of the things i love about diy, failing and trying to solve problems. I'm sure that something interesting and useful will come out!
I took your data and processed some statistics
I also computed Rds0, which represents the channel resistance of the JFET,
gm0 = yfs0 = 2*Idss/Vp
Rds0 = 1/gm0
Typically J201's are around 600 or so.
2N5457's and many other JFETS are around 200.
Your JFETs are around 200ohms, more like 2N5457's with low Vp's.
Device Vp [mV] Idss [mA] Rds0 [ohm]
avg 540.2 1.34 207.4
min 365.0 1.01 100.3
max 765.0 1.82 369.8
sd 114.2 0.22 57.3
sd% 21.1 16.7 27.6
avg-3sd 197.5 0.67 35.4
avg+3sd 882.9 2.01 379.4
Quote from: Rob Strand on December 19, 2018, 05:00:43 PM
I took you data and processed some statistics
I also computed Rds0, which represents the channel resistance of the JFET,
gm0 = yfs0 = 2*Idss/Vp
Rds0 = 1/gm0
Typically J201's are around 600 or so.
2N5457's and many other JFETS are around 200.
Your JFETs are around 200ohms, more like 2N5457's with low Vp's.
Device Vp [mV] Idss [mA] Rds0 [ohm]
avg 540.2 1.34 207.4
min 365.0 1.01 100.3
max 765.0 1.82 369.8
sd 114.2 0.22 57.3
sd% 21.1 16.7 27.6
avg-3sd 197.5 0.67 35.4
avg+3sd 882.9 2.01 379.4
Thanks a lot! , i guess they will be useful in some way.
i don't know much about calculations and jfets, but that's a perfect excuse to learn more stuff about them . I should measure my to92 2n5457's and do the same calculations as you did and see where they belong. Thank you very much!
Quotei don't know much about calculations and jfets, but that's a perfect excuse to learn more stuff about them
A good start is the Fetzer calculator that rankot mentioned a few posts back.
It's at the bottom of this page,
http://runoffgroove.com/fetzervalve.html
JFETs are tricky things to deal with because they have wide tolerances. That's why you will see a lot of designs with Trimpots on the drain resistors. I put-up a lot of results a year or so ago. The main aim was to show how the designs and performance changes when you consider the JFET tolerances. I include the Fetzer method and it gives quite useable results.
Quote from: Rob Strand on December 19, 2018, 05:30:33 PM
Quotei don't know much about calculations and jfets, but that's a perfect excuse to learn more stuff about them
A good start is the Fetzer calculator that rankot mentioned a few posts back.
It's at the bottom of this page,
http://runoffgroove.com/fetzervalve.html
JFETs are tricky things to deal with because they have wide tolerances. That's why you will see a lot of designs with Trimpots on the drain resistors. I put-up a lot of results a year or so ago. The main aim was to show how the designs and performance changes when you consider the JFET tolerances. I include the Fetzer method and it gives quite useable results.
I understand, my knowledge on jfets are , correct me if I'm wrong
- in production they make jfets, a lot of them, then they sort them out in some specs because manufacturer can't be sure about how they will end up, like CPU manufacturing, they just produce them then sort them depending their performance. That's why they have wide tolerance hence in some designs , designer needs to put trimpots etc to compansate that tolerances.
- they are similar to tubes without pilot lights, I have a little bit knowledge of basics about tubes. Which I can relate to your calculations
I'm so grateful for your time to answer my question and helping me out to understand electronics better
QuoteI understand, my knowledge on jfets are , correct me if I'm wrong
That's a good start.
The only thing I can add is you will see them used as voltage-controlled-resistors (VCR) in Phasers, Compressors, Tremolo's. When the voltage across the drain (D) and the source (S) is small they behave a little differently.
You will also see them used as constant-current sources but this isn't used so much in effects pedals.
Quote from: Rob Strand on December 19, 2018, 06:03:50 PM
QuoteI understand, my knowledge on jfets are , correct me if I'm wrong
That's a good start.
The only thing I can add is you will see them used as voltage-controlled-resistors (VCR) in Phasers, Compressors, Tremolo's. When the voltage across the drain (D) and the source (S) is small they behave a little differently.
You will also see them used as constant-current sources but this isn't used so much in effects pedals.
Now,for me , it makes more sense, thank you again!
Those all look like fine amplifiers, in a stage working around a half a mA, source resistor 400-500 Ohms, drain resistor 10K.
Quote from: Rob Strand on December 19, 2018, 05:30:33 PM
JFETs are tricky things to deal with because they have wide tolerances.
jFET's are only tricky when one doesn't bother measuring Idss and Vgs(off) per device
and instead rely on the vague idea of manufacturing tolerances ... with their arbitrary widths, etc.
all small signal jFET's are more or less the same in function
parametrically different maybe in the parasitic capacitance part and operating ranges
the later usually not affecting use much in our 9v world
otherwise, with the same input/output mapping shape, stretched or scaled by Idss and Vgs(off) "limit" values
...
maybe not a bad idea to characterize jFET's (fake, mis-labelled, or otherwise) and catalogue them by their Vgs(off) value
this at least will give us the opportunity to pair or quad them together for VCR applications (eg., phasors) if we want to go the "matched" route, and in that application Vgs(off) can then also tell us what Zener bias voltage be required to bias them properly, etc ...
nothing tricky or weird about jFET's ... if you "know" what you're working with
Quote from: Rob Strand on December 19, 2018, 05:00:43 PM
I took your data and processed some statistics
I also computed Rds0, which represents the channel resistance of the JFET,
gm0 = yfs0 = 2*Idss/Vp
Rds0 = 1/gm0
Typically J201's are around 600 or so.
2N5457's and many other JFETS are around 200.
Your JFETs are around 200ohms, more like 2N5457's with low Vp's.
Device Vp [mV] Idss [mA] Rds0 [ohm]
avg 540.2 1.34 207.4
min 365.0 1.01 100.3
max 765.0 1.82 369.8
sd 114.2 0.22 57.3
sd% 21.1 16.7 27.6
avg-3sd 197.5 0.67 35.4
avg+3sd 882.9 2.01 379.4
Thanks for the equations! How would one calculate the gate voltage required for a particular resistance (say, 10k)?
Quote from: abakuzam on December 19, 2018, 08:00:40 AM
I measured 36 of the J201 jfets, can't find the rest of them , probably, under my bed ahah :D
i measured vgsoff with this : https://www.rullywow.com/jfet-matcher-project-vgsoff/
Idss with this : http://stompville.co.uk/?p=112
I used same 9v regulated power supply , these are my results:
Note: i didn't bother to put -0,xxx type of measurement for vgsoff, you can put -0, at the begining of the numbers.
Vgsoff values seems to in spec but Idss values are waay out of specsi checked my smd j201's (mmbfj201) they all seem to be in specs.
VGS(off)
Volts Idss mA
488 1,54
522 1,15
668 1,23
424 1,23
442 1,73
460 1,42
620 1,19
698 1,51
696 1,52
618 1,24
448 1,58
406 1,3
600 1,65
452 1,45
610 1,12
625 1,31
450 1,41
485 1,16
460 1,15
436 1,64
747 1,01
637 1,76
765 1,13
424 1,17
443 1,02
589 1,07
374 1,11
585 1,51
512 1,19
451 1,18
753 1,48
365 1,82
526 1,14
490 1,3
638 1,47
Year's ago I've made a jfet calculator: http://www.diydave.be/tools/fetcalc/index_eng.html (http://www.diydave.be/tools/fetcalc/index_eng.html)
Since you have Vp and Idss for every fet, it's a "walk in the park" to get Rd and Rs to get your fet working.
E.g, the last one: if you put in the numbers, and want a mid-bias for Vgs and Vd, you get Rs = 870 ohm and Rd = 11k.
QuoteThanks for the equations! How would one calculate the gate voltage required for a particular resistance (say, 10k)?
You should be able to find all the JFET equations on the web and also many pages about JFET biasing. Some will make sense to you and some won't. Just dig around until you find one you like.
Equation 1 from here is the basic JFET equation, most results follow on from that,
www.kennethkuhn.com/students/ee351/jfet_basics.pdf
You have to watch out for the signs of VP and VGS so I'm writing it like this,
ID = IDSS * [1 + (VGS/ |VP|) ]^2 (eqn 1)
where VGS is negative.
We can re-write this as,
VGS = |VP| (sqrt(ID/IDSS) -1) (eqn 2)
The above equations are just for the JFET.
For biasing you might typically Bias the drain voltage at 4.5V for a 9V supply. That mean the voltage across the drain resistor is (9-4.5) = 4.5V and the current through the 10k drain resistor is ID = 4.5V / 10k = 0.45mA. So you take that value and your JFET parameters |VP| = 0.5V and IDSS=1mA and plug then into (eqn 2)
VGS = 0.5 * (sqrt(0.45/1.0) - 1) = -0.16V
FYI, the Fetzer calculator *starts* with VGS/|VP| = -0.35 and then calculates RD.
QuotejFET's are only tricky when one doesn't bother measuring Idss and Vgs(off) per device
and instead rely on the vague idea of manufacturing tolerances ... with their arbitrary widths, etc.
OK for home but not for production. For phasers you don't have much choice but to measure since you already know the device tolerances are too wide to build a circuit that will work - even with a variable bias pot.
Quote from: stallik on December 18, 2018, 03:13:31 PM
Couple of years back, I had 2 fake 201's. At least I think they were fake. I'd tried one in a Mayqueen and they didn't work until I use a 20x trimmer to bias them (by ear) and even then the sweet spot was within about 1/4 turn. I ended up with a great sounding pedal with so much bass that only some amps can handle it. I posted about it here at the time.
Earlier this week I started to build for a friend an 18V ep booster, but it wasn't sounding right. I used an 2N5457. Drain resistor is 8k2 on the original. Today I adjusted the bias to half the supply. Used a 20K pot, then a 50K pot, a 100K pot and finally a 250K until I got half the supply (167K resistance). Now I'm hoping the mriend don't like the sound of this booster, so I can keep it :icon_twisted:
Quick! Build him another ;)
As a related aside... I just got fake 2N5458's. Same issue, very low gain.
MC
Quote from: Rob Strand on December 20, 2018, 04:15:19 PM
OK for home but not for production.
DIY is about doing at home what THEY won't do at the factory ...
;)
if that's what's needed to give your home-made product an edge, why not ... ?!
Quote from: italianguy63 on December 21, 2018, 04:14:38 AM
As a related aside... I just got fake 2N5458's. Same issue, very low gain.
MC
Could anyone suspecting fake parts post average Idss/Vgs(off) values, so we can have a better idea about a quality of parts we have? What is the source of your fake parts, too, so we know what to avoid?
Here is a plot of Idss and Vp that I made from several batches of TO-92 JFETs that I have. Everything here is genuine except for 10 putative J201s. These were bought from a US ebay seller before J201s completely dried up, I knew they would likely have some issues, but felt they might not be complete duds. This turned out to be the case: they are real JFETs but out of spec, which is fine as long as I know it. The values of Idss and Vp were measured with the simple test circuit on the Runoffgroove Fetzer Valve webpage.
(https://i.postimg.cc/630F3mRc/fet-alltypes-props.png) (https://postimages.org/)
The way that a Fetzer-type gain stage is biased, if you substitute a JFET with larger -Vp, then to bias it you need a smaller drain resistor and the gain is reduced. Thus if you substitute a 2N5457 for a J201, the gain winds up lower and you get a different-sounding pedal.
Those are my values:
(https://i.postimg.cc/fW69Yrmg/jfet-tabela.jpg)
reddesert - your off j201's look quite a bit like on j202's.
hook 'em up to your breadboard with a variac, and juice 'em as a sacrifice til the magick smoke goes out to the mojo gods.
I have recently bought few MMBFJ201 JFETs, Idss is around 0.4mA, Vgs(off) is around 0.3V (lowest part of specs), measured with GM328A transistor tester (which gives slightly lower values than ROG measurement method). Any ideas what to do with them?
Even the most out-of-spec JFETs can make wonderful buffers. Wire them up as a source-follower and put front-and-center as a high-impedance front end, driving a tone stack, following a high output-impedance gainstage, or at the tail end driving a 10K volume pot. Basically anywhere you'd normally put an op-amp non-inverting buffer and gain wasn't a primary concern.