# JFETS, matching etc.



## Flying

There are a number of projects here that require JFETS, my electronics knowledge is still in the painting by numbers phase with the odd glimmer of dawning realisation, that I'd hesitate to describe as understanding!

So please humour me if I ask a few, probably, dumb questions about JFETS

First off I don't think there are any phaser project on here that require matched FETS, but what about when used in a Mu-Amp configuration such as the Six String Stinger? Or in the configuration such as in the Cobalt Drive?


----------



## Chuck D. Bones

Matching is not required with mu-followers.  The bottom FET sets the drain current for both FETs, The top FET sets the drain voltage for the bottom FET.

It's funny you mention phase-shifters, because tracking is important.  Small Bear sells matched JFETs for that very reason.  The phase-shifters here are LDR-based.  I doubt that very many people check the matching on their LDRs.


----------



## Mourguitars

Do the testers work ? I started watching youtube , one guy used a tester another used a bread board..another doing some math...ill wait for a answer like CDB said...my brain got a little twisted on youtube lol , don't mind learning but i am like Flying...paint by numbers !

Mike


----------



## Nostradoomus

Speaking of matching fets and phasers...this project is tantalizing.










						viva Analog "Paradigm Shifter" (DIY) // jcm(c)2017 -
					

original concept JC Maillet (c) 2017 PREFACE As far as building jFET phasor circuits goes the going assumption is to make use of well-matched jFET devices operating as variable resistance elements. That assumption is based on another assumption; namely, that …  viva Analog “Paradigm Shifter”...




					viva-analog.com


----------



## bergera

I have 


Mourguitars said:


> Do the testers work ? I started watching youtube , one guy used a tester another used a bread board..another doing some math...ill wait for a answer like CDB said...my brain got a little twisted on youtube lol , don't mind learning but i am like Flying...paint by numbers !
> 
> Mike


A tester from amazon and I made a tester from rullywow or madbean and they correspond to each other. I've build two nom-nom phasers from madbean which quad sets that I matched myself.

I haven't tried useding matches ones in other pedals but I've wondered about it just like you..


----------



## Mourguitars

Cool, ill buy the one from Amazon...i like tools and i like buying more tools ! lol

Mike


----------



## Flying

Thanks for the clarification on the Mu-Follower Chuck D. Bones, that's good to know.



Chuck D. Bones said:


> ...It's funny you mention phase-shifters, because tracking is important.  Small Bear sells matched JFETs for that very reason.  The phase-shifters here are LDR-based.  I doubt that very many people check the matching on their LDRs.


Guilty as charged, didn't even think about it when putting together my 'Depths' I guess the inverse square law of light would also have an effect if the LDRs are not absolutely the same distance from the LED. Despite all that it still sounds pretty good to my ears 

The only tester I have is this one attached which Chuck has already said is a bit limited in another thread.


----------



## Chuck D. Bones

Not just different amount of light, but the light resistances can be over the place for the same illumination.  As you say, it sounds good and that's all that really matters.

I wasn't criticizing the tester, I've got one or order now.  It's useful for identifying and health checking transistors of all types.  My point was you need at least two data points to be able to predict the drain current as a function of gate voltage.  Or, in the case of phase-shifters, drain-source resistance as a function of gate voltage.


----------



## bergera

I have this one

Transistor Tester, DROK Mosfet... https://www.amazon.com/dp/B01MS1FOYM?ref=ppx_pop_mob_ap_share

Used it for jfets,transistors, and resistors so far.


----------



## Mourguitars

bergera said:


> I have this one
> 
> Transistor Tester, DROK Mosfet... https://www.amazon.com/dp/B01MS1FOYM?ref=ppx_pop_mob_ap_share
> 
> Used it for jfets,transistors, and resistors so far.



I bought the same one

Mike


----------



## K Pedals

bergera said:


> I have this one
> 
> Transistor Tester, DROK Mosfet... https://www.amazon.com/dp/B01MS1FOYM?ref=ppx_pop_mob_ap_share
> 
> Used it for jfets,transistors, and resistors so far.


Yeah I got this one too...


----------



## Mourguitars

Got my new tester in today , tried 2 different bags of  (10 ) J201's from 2 different sources  ...getting some mixed results as below...both have a F0525-j201 same writing...

batch that came in a nice silver foil sealed bag reads :

BJT-NPN
123=ECB
hFE=191
Vf=669mV
Some tested 171, 188 on the hFE

This batch next reads something different came in a plain baggie that reads :

N-JFET
123=SDG
I=0.71mA
Vgs=0.50V

Don't know what I'm looking at Guys !

There different ..im sure i got bite of the Evil bay

Let me know

Mike


----------



## K Pedals

Mourguitars said:


> Got my new tester in today , tried 2 different bags of  (10 ) J201's from 2 different sources  ...getting some mixed results as below...both have a F0525-j201 same writing...
> 
> batch that came in a nice silver foil sealed bag reads :
> 
> BJT-NPN
> 123=ECB
> hFE=191
> Vf=669mV
> Some tested 171, 188 on the hFE
> 
> This batch next reads something different came in a plain baggie that reads :
> 
> N-JFET
> 123=SDG
> I=0.71mA
> Vgs=0.50V
> 
> Don't know what I'm looking at Guys !
> 
> There different ..im sure i got bite of the Evil bay
> 
> Let me know
> 
> Mike


I just got some smd J201s from Tayda reading NPN... they’re supposed to be JFET...


----------



## Mourguitars

K Pedals said:


> I just got some smd J201s from Tayda reading NPN... they’re supposed to be JFET...



I have those in my cart from Tayda , going to get the boards here...head scratch ! hmmm ....im sure the smart ones here will chime in !


----------



## Chuck D. Bones

And that's why I don't buy semiconductors on eBay.  Even the honest vendors have no clue how to handle & package semiconductors to prevent ESD damage.  The only time I tried buying a semiconductor on eBay was an AMD processor.  It came taped to a piece of cardboard with packing tape.  I immediately sent it back.  I've seen some tasty Ge transistors on eBay, but they are untested and are almost as expensive as known good ones from SB.

The correct pinout for J201 is DSG.  It's possible the tester got confused on the 2nd batch because in many circuits, S & D are interchangeable. 
I < 1mA is plausible for J201.
Vgs between 0.3 and 1.5 is in spec.
What I don't know about these testers is whether the I reported is Idss (Id with Vgs=0) or Id with the Vgs shown.  Likewise, does Vgs = Vp (Vgs when Id=0) or is it just some test voltage?

That first batch, try turning them around and measuring again.  Is the font the same on the two batches?  Same color ink?

Here's a quick check to see if the device is a JFET or a BJT.  Use a DVM to measure the resistance between S & D.  Should be <100 Ohms and the same in both directions if it's a JFET.  Set the DMM to the 2K range.


----------



## temol

Ok.. Tayda jfets are jfets.. thats' t the meter probably.
Those cheap LCR meters are not the best choice for JFET measuring. I have one and do not use it for jfets because readings are off. 

Mourguitars - can you measure the same transistors with this simple setup?




T.


----------



## Flying

I've just pulled a MMBFJ201 out of it's plastic tray and I get the following test results:

ID=0.3mA@Vg0.21V


----------



## K Pedals

Mourguitars said:


> I have those in my cart from Tayda , going to get the boards here...head scratch ! hmmm ....im sure the smart ones here will chime in !


I’ve never got any bad parts from them before I think they probably just sent the wrong parts...


----------



## Mourguitars

temol said:


> Ok.. Tayda jfets are jfets.. thats' t the meter probably.
> Those cheap LCR meters are not the best choice for JFET measuring. I have one and do not use it for jfets because readings are off.
> 
> Mourguitars - can you measure the same transistors with this simple setup?
> View attachment 1344
> 
> T.




Will do...ill use the meter and write down the results..



Chuck D. Bones said:


> And that's why I don't buy semiconductors on eBay.  Even the honest vendors have no clue how to handle & package semiconductors to prevent ESD damage.  The only time I tried buying a semiconductor on eBay was an AMD processor.  It came taped to a piece of cardboard with packing tape.  I immediately sent it back.  I've seen some tasty Ge transistors on eBay, but they are untested and are almost as expensive as known good ones from SB.
> 
> The correct pinout for J201 is DSG.  It's possible the tester got confused on the 2nd batch because in many circuits, S & D are interchangeable.
> I < 1mA is plausible for J201.
> Vgs between 0.3 and 1.5 is in spec.
> What I don't know about these testers is whether the I reported is Idss (Id with Vgs=0) or Id with the Vgs shown.  Likewise, does Vgs = Vp (Vgs when Id=0) or is it just some test voltage?
> 
> That first batch, try turning them around and measuring again.  Is the font the same on the two batches?  Same color ink?
> 
> Here's a quick check to see if the device is a JFET or a BJT.  Use a DVM to measure the resistance between S & D.  Should be <100 Ohms and the same in both directions if it's a JFET.  Set the DMM to the 2K range.



I like many,  went to Youtube and watch a few vids on testing with the meter..he said the flat part goes down, not up on the tester i will try both ways...


----------



## temol

You can also try "circuit" described here (bottom of the page) http://www.runoffgroove.com/fetzervalve.html
Also here - https://viva-analog.com/jfet-characterization-technique-using-only-9v-battery-and-dmm/

T.


----------



## Chuck D. Bones

temol said:


> Ok.. Tayda jfets are jfets.. thats' t the meter probably.
> Those cheap LCR meters are not the best choice for JFET measuring. I have one and do not use it for jfets because readings are off.
> 
> Mourguitars - can you measure the same transistors with this simple setup?
> View attachment 1344
> 
> T.


Be damned sure you have a FET and it's hooked up the right way.  Hook it up wrong or try that with a BJT and you could burn it up.  If you want to do this safely, put a 10K resistor between the battery + terminal and the JFET drain.

Respect to the guys at Runoffgroove!


----------



## Mourguitars

I sent Mr Pedalpcb a pic that I can’t upload , but I wrote down all the readings..I got readings all over the place like CDB said above I had FETs and BJTs so I didn’t want to do that test  other than the meter

Mike


----------



## temol

I've never worried about any protection because I have dedicated adapter for smd, socket for through hole and I do not mix bjt and fet stuff 
But of course it's a good advice.

T.


----------



## Mourguitars

page-12

Heres my readings i took with a tester, all over the map and 2 different types..file is to big to post here so i uploaded it over there 

Mike


----------



## temol

Cannot view the file -  "You must be logged in to do that."

T.


----------



## Mourguitars

I tried a phone pic , iPad pic...all to large to upload, I’ll work on it


----------



## Nostradoomus

Upload to imgbb.com or something like that


----------



## Mourguitars

View attachment 1355


----------



## Mourguitars

phone pic..let me get it right..well upright


----------



## Mourguitars




----------



## Mourguitars

Some are N-JFET and the others are BJT_NPN ? Got these off eBay ..so ............?


----------



## temol

Those jfet readings are from LCR meter or DMM? Suspiciously good as for ebay 201's...

T.


----------



## Mourguitars

Transistor Tester, DROK Mosfet Transistor Capacitor Tester, Mega328 NPN PNP Transistor Diode Resistor Inductor Capacitance MOS SCR ESR Meter Automatic Checker Detector - - Amazon.com
					

Transistor Tester, DROK Mosfet Transistor Capacitor Tester, Mega328 NPN PNP Transistor Diode Resistor Inductor Capacitance MOS SCR ESR Meter Automatic Checker Detector - - Amazon.com



					www.amazon.com


----------



## temol

Can you take one of the J201 transistors and make comparison of Vgs readigns from DMM method and transistor tester?

T.


----------



## Mourguitars

temol said:


> Can you take one of the J201 transistors and make comparison of Vgs readigns from DMM method and transistor tester?
> 
> T.


 
Yea, ill try later today..

Mike


----------



## Chuck D. Bones

My transistor tester arrived yesterday.


 
What a cool device!  Measures wah inductors no problem.  I tried measuring a guitar pickup, but the winding resistance is so high that the tester thinks it's a resistor and can't measure the inductance.  Try testing 2-color LEDs in a darkened room... it's a mini light show!  
Only complaint is that it doesn't measure Idss & Vp on JFETs.  I still have to do that manually until I can find my Heathkit curve tracer.  Assembling the case is tricky, it's like building a house of cards.  I wasn't going to cheat & use tape.
Warning: don't try to use a guitar pedal power supply to power this up because this thing is wired for a *positive *center pin.  When I'm not using a 9V battery, I'm powering it with a 12VDC power supply left over from an old router.


----------



## zgrav

Where did you order that kit?  That looks like an interesting kit that makes a useful tool.


----------



## Chuck D. Bones

https://www.ebay.com/itm/2019-Versi...ance-ESR-meter-Signal-Generator/182678167951?

I bought the assembled board with the clear case.  The case has two tops, one that covers everything except the dial & ZIF socket, one that covers the top half of the board only.  Mine is assembled with the top half cover.  I tried the full cover, but the ZIF lever is too hard to get at and the knob wasn't pefectly centered and dragged on the cover.  You can buy the board fully assembled, or a kit of parts with instructions.  There is a ton of info here.


----------



## zgrav

Thanks.  Will check that out.  Hard to argue with paying less than $4 more to get the assembled board instead of the DIY kit.


----------



## Mourguitars

These were not to bad to do once i got a system that worked for me they all tested in the same ball park vs the other pic i posted of the Ebay J201's...those might be good but my first two builds used them and didn't turn out so well..im pretty gun shy on using them.

Mike



https://imgur.com/3EQgA3Y


----------



## Chuck D. Bones

Follow-up on the transistor tester...
It measures germanium transistors correctly - it accounts for leakage (Iceo) when measuring and calculating current gain (hFE).  I checked a few Ge transistors using the tester and the "Bare Bones" method and they correlate.  To quote Steve Daniels of Small Bear Electronics: "The temperature sensitivity of older germanium transistors has to be seen to be believed..."  This is no exaggeration.  Whatever method you use for measuring Ge transistors, they have to temperature stabilize before you can get a useful reading.  The heat from your fingers can drive the leakage up 4x or more with some transistors.  It can take several minutes for the device to cool down and stabilize after handling.

The diode test current is fairly high, causing some diodes (the ones with higher resistance) to read an abnormally high Vf.  Those I test with a DMM.


----------



## Nostradoomus

Yeah I’ve done a just for fun experiment of rubbing GEs between my fingers before testing them and it’s ridiculous


----------



## JetFixxxer

Chuck D. Bones said:


> My transistor tester arrived yesterday.
> View attachment 1470
> What a cool device!  Measures wah inductors no problem.  I tried measuring a guitar pickup, but the winding resistance is so high that the tester thinks it's a resistor and can't measure the inductance.  Try testing 2-color LEDs in a darkened room... it's a mini light show!
> Only complaint is that it doesn't measure Idss & Vp on JFETs.  I still have to do that manually until I can find my Heathkit curve tracer.  Assembling the case is tricky, it's like building a house of cards.  I wasn't going to cheat & use tape.
> Warning: don't try to use a guitar pedal power supply to power this up because this thing is wired for a *positive *center pin.  When I'm not using a 9V battery, I'm powering it with a 12VDC power supply left over from an old router.




Since I wind my pickups I picked up a cheap LCR MS8269 from Amazon to measure pickups. Not sure how accurate it is since I don't have anything to compare it to.   Even then people still think that DCR is the way to measure pickup output and really don't care about the inductence.


----------



## Chuck D. Bones

I think the reason most people measure pickup resistance is a) it's an easy measurement to make and b) they don't know what inductance is.  If you want a good idea of how the pickup will sound before you install it, you need to measure the impedance as a function of frequency.  I do it the hard way with a functions generator and an oscilloscope.  That method is good enough to tell if a pickup's cover is brass or nickel-silver.  The hard-core guys use a pickup driver and a network analyzer.  An LCR meter will measure the impedance at one frequency and not know anything about resonance.  If the measurement freq is low enough (1KHz or lower), then it's measuring mostly inductance and resistance.


----------



## JetFixxxer

Dave of Sigil Pickups helped me a lot when I first go into winding and he suggested the Syscomp CGM-101. Was never in stock and always unavailable so I got myself a Hantek 6022be and eventually two other Oscilloscope. Now I haven't wound pickups over a year as pedals have taken my over my spare time


----------

