j201 substitute

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j201 substitute

Postby POTL » 24 Apr 2019, 00:41

Hello everyone, I recently encountered a j201 deficit in my country, having studied the forums I found several models that other manufacturers use (mmbf4393 Catalibread and 2SK208 AMT) or recommend stores (PF5102 Smallbear).
I also found some more options in stores.
If someone used them, then tell us about your experience.
I use them to create amps in the box, in the style of fetzer, like JHS Superbold, Wampler Tweed 57 and many other manufacturers.
Here is my list of possible replacements:
Model VGS(off) IDSS
J113 0.5-3 V 2 mA
PF5102 0.7-1.6 V 4-20 mA
MMBF5484 0.3-3 V 1-5 mA
MMBF4393 0.5-3 V 5-30 mA
2SK208 0.4-5 V 0.3-0.75 mA
BF862 0.3-1.2 V 10-25 mA
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Re: j201 substitute

Postby Optical » 24 Apr 2019, 02:08

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Re: j201 substitute

Postby Manfred » 24 Apr 2019, 08:47

I had a look at the datasheets of the JFETs form the list.
IMO there is no direct replacement possible in each case the circuitry must be adapted,
because there is no match with the forward transconductance ranges.

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Re: j201 substitute

Postby POTL » 24 Apr 2019, 12:55


Mouser is not convenient, plus they require payment coil at $ 7 and they have an expensive delivery.
I think that you can change the trimmer resistors for the correct offset.
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Re: j201 substitute

Postby POTL » 24 Apr 2019, 12:58

Manfred wrote:I had a look at the datasheets of the JFETs form the list.
IMO there is no direct replacement possible in each case the circuitry must be adapted,
because there is no match with the forward transconductance ranges.


If you believe the site ROG, then only VGSoff and IDSS are important.
Are you talking about Yfs?
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Re: j201 substitute

Postby Manfred » 24 Apr 2019, 14:46

If you believe the site ROG, then only VGSoff and IDSS are important.
Are you talking about Yfs?


Yfs is a function off VGSoff, IDSS and the drain current ID:
Yfs = (2/VGSoff)*sqrt(ID*IDSS)

I talking about Yfs, because Yfs and Rdrain determines the open loop stage gain.
Maybe an other JFet achieves the wished Yfs but not for the same drain current,
it is therefore necessary to adapt the circuitry, as already mentioned above.

The ranges of IDSS and VGSoff for the J201 are as follows:
0,2 to 1 Milliamps
0,3 to 1.5 Volts

No JFET of the list provides a good approximation, either the IDSS range or the VGSoff range are nearby but not both ranges together,
so, in my experience, is a direct substitution by another JFET not easily possible.
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Re: j201 substitute

Postby Manfred » 26 Apr 2019, 19:33

In order to show you the differences I have done a small experiment and ran a simualtion with a substitution of the J201 by the MMBF4393LT1G JFet.
I loan the circuit from the Peppermill Overdrive which is designed as a clipper circuit.
The Rd set up so that a symmetrisch clipping were achieved.
After I replaced the J201 by the MMBF4393LT1G the circuit no longer works.
I changed Rdrain and Rsouce until the adapted circuit had the same behavior.
Have a look at the different read values.
This demonstrates that a direct replacement is not easily possible.
FetSubstitute.JPG
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Re: j201 substitute

Postby POTL » 28 Apr 2019, 11:18

Manfred wrote:In order to show you the differences I have done a small experiment and ran a simualtion with a substitution of the J201 by the MMBF4393LT1G JFet.
I loan the circuit from the Peppermill Overdrive which is designed as a clipper circuit.
The Rd set up so that a symmetrisch clipping were achieved.
After I replaced the J201 by the MMBF4393LT1G the circuit no longer works.
I changed Rdrain and Rsouce until the adapted circuit had the same behavior.
Have a look at the different read values.
This demonstrates that a direct replacement is not easily possible.
FetSubstitute.JPG


thank
I will try them in the real world)
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Re: j201 substitute

Postby Manfred » 28 Apr 2019, 14:43

I will try them in the real world


With which substituded JFET you intend to make a trial run.
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Re: j201 substitute

Postby temol » 28 Apr 2019, 17:55

Hi Manfred,

how about sine shape and frequency response of the stage after adaptation? Are they identical to the J201?

T.
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Re: j201 substitute

Postby Manfred » 28 Apr 2019, 21:28

temol wrote:Hi Manfred,

how about sine shape and frequency response of the stage after adaptation? Are they identical to the J201?

T.


Hi Temol,

I changed the resistor values until the clipping curve achieved virtually the same shape,
I was not watching the frequency respones.
I imagine that the source capacitor has to be adapted accordingly to keep the frequency behaviour.
I going to read the curves an attache it to the next post.
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Re: j201 substitute

Postby J0K3RX » 29 Apr 2019, 15:08

FYI.. While comparing specs I stumbled upon SST201-T1-E3 which is the Vishay part# for the MMBFJ201. I have seen a few suppliers with allot still in stock probably because not many customers are aware of the different part number. They are End of Life also so, ya might wanna consider grabbing a few thousand or more, sit on them for 6 months or a year and then sell'em for double or tripple your cost... :twisted:

Datasheet
http://www.farnell.com/datasheets/91001 ... ZgQAvD_BwE

Mouser has 63,868 in stock and the price isn't too bad in quantites of 100 @ $0.69 each.
Qty: 1 - $1.09
Qty: 10 - $8.93
Qty: 100 - $68.60

https://www.mouser.com/ProductDetail/Vi ... G0EALw_wcB

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Re: j201 substitute

Postby Manfred » 29 Apr 2019, 23:47

As promissed here the comparison of the output curve traces:
OutputCurveTraces.jpg

The source capacitor determines the inflexion point of the frequency curve.
I found a value of 0.33 Microfarads for the circuit using the MMBF4397 JFet to achieve the inflexion point in the same frequency range.
I am not happy with the low end of the frequncy response, so I have to carry out further research.
FrequencyResponses.jpg
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Re: j201 substitute

Postby temol » 30 Apr 2019, 10:47

Thanks for the comparison traces.
I expected that frequency response plots won't match.
Do you have MMBF4393 ltspice model you can share?

T.
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Re: j201 substitute

Postby Manfred » 01 May 2019, 01:34

Hi Temol,

I using another obsolete simulation software.
I picked the data from the spice view of the MMBF4393 model there.
I hope you can use it in this form:
+ (
+ VT0=-1.36506 BETA=0.0190655 LAMBDA=0.0227922 RD=76.4299 RS=38.7311
+ CGS=2.94972e-012 CGD=8.23801e-012 PB=0.18649 IS=1e-014 FC=0.5
+ KF=1e-020 AF=0.2
+ )
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Re: j201 substitute

Postby Manfred » 01 May 2019, 19:10

I worked on the adaption an found the following circuit as best approximation regarding to the clipping behaviour and the frequency response.
In summary, it was shown that the substitution of JFETs is not easily possible.
MMBF4393LT1G_2ndAdaption.JPG

Responses10Hz_to_10kHz_2.jpg
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Re: j201 substitute

Postby POTL » 01 May 2019, 20:11

I ordered adapter cards from to-92 to sot23 and wait for them.
I looked at the digikey and mouser sites that most of the popular jfet are no longer produced, but the following are still available:
J113
MMBF4393
2SK208-R
2SK209-Y
MMBFJ270
MMBFJ177
MMBFJ309
2SK3666-2

Most likely, closer to the summer I will write which transistors work well.
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Re: j201 substitute

Postby temol » 01 May 2019, 21:37

POTL - where did you order the adapter boards? China? Last time I've checked ali and ebay, probably all of the cheap adapters had "wrong" pinout. 2-3-1 instead of 3-2-1.

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Re: j201 substitute

Postby dv8r601 » 01 May 2019, 23:51

temol wrote:POTL - where did you order the adapter boards? China? Last time I've checked ali and ebay, probably all of the cheap adapters had "wrong" pinout. 2-3-1 instead of 3-2-1.

T.


As a side note on those shitty adapter boards, you can mount the sot23 transistor sideways and fix that pinout issue, i did it with mmbf4393 to match normal dsg instead of dgs pinout.
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Re: j201 substitute

Postby POTL » 02 May 2019, 01:00

Yes, I ordered them in China. Pinout does not play any role for me, since I use solderless development boards.
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