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

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.

...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]

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]

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]

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]

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]

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]

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..

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.