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Old 10th April 2013, 05:42 PM   #411
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Quote:
Originally Posted by pidigi View Post
I was thinking that the matching (in Idss AND Vgs(off)) is important, but you are saying that the difference in Vgs(off) of a factor of 2 is good, right?
When you say that "Finally I found better matched pairs jfets j113/j175 at Idss 25.5mA", is this meaning that you have selected 2 x 4 fets (2 pieces J113 and 2 pieces J175 for each channel) that have Idss = 25.5mA? And what about Vgs(off)?
As Andrew said, the curve Id vs Vgs should be equal in order to consider them matched, and I don't understand if you matched them for Idss, Vgs(off), both or none....

Thanks for your informations,

Paolo
Paolo,
Vgs(off) is graphical curve produced by a manufacturer in order to facilitate users. because at the beginning we do not know which one part to buy (j112 or j113). What we know in the begining are that we need for example jfets with 22mA at Idss. Now we look at datasheet graphic "Transfer Characteristics" and you will see that the part wiht 22mA Idss have curve with Vgs(off)=-2V. Again at datasheet we will see that the part J113 have Vgs(off) from -0.5 to -3V or average Vgs(off) =-1.75V. For J112 average it will be Vgs(off)=-3V. Now if you buy 100 pcs. from J113 and J112 and measure them you will see that from J113 you will have more jfets with 22mA than J 112. About matching procedure please read here:
http://www.geofex.com/article_folder...h/fetmatch.htm
Regards
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Old 10th April 2013, 11:42 PM   #412
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Quote:
Originally Posted by gk7 View Post
Ok, sorry havenīt looked at the 2N5461 datasheet.

For the distortion spectra: What I meant was to compare the Toshiba FETs I use
and the J113/J175 from current production. Additionally I have an original module
too. I donīt think John has made such a comparison, he designed this line stage
40 years ago and the FETs originally used are not made any more since decades.
Georg,
I have not 2sj74 on stock. Also I have not necessary equipment to make this test valid. If you want I will send to you perfectly matched pairs J113/j175 and 2n4401/03 to make this test and to compare the results with Toshiba FETs. And before 40 years ago and now the required jfets specification for JC2 are the same - high input impedance, low input capacitance, high gm, low noise, high current, low Rds on. Except for the noisy j175 everything seems to be ok for j113/j175. Do you have 2sk246/2sj103 on stok? Do you make test between 2sk170/2sj74 and 2sk246/2sj103? Also can you measure the power consumption of the origial line modul and output dc offset?

Regards
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Old 11th April 2013, 09:27 AM   #413
gk7 is offline gk7
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Location: Vienna, Austria
Quote:
Originally Posted by ivodonchev View Post
Georg,
If you want I will send to you perfectly matched pairs J113/j175 and 2n4401/03 to make this test and to compare the results with Toshiba FETs.
Thank you for the offer, but I donīt have line module boards left and
currently have no plans to have new ones made.

Quote:
Originally Posted by ivodonchev View Post
Except for the noisy j175 everything seems to be ok for j113/j175.
Well yes of course, I actually regard that as good news because they
are still available while Toshiba seems not to make any p-channel FETs
any more.

Quote:
Originally Posted by ivodonchev View Post
Do you have 2sk246/2sj103 on stok? Do you make test between 2sk170/2sj74 and 2sk246/2sj103?
No and no. I have built my replacement modules with quad matched 2SK170V / 2SJ74V
parts which were still available at the time:
Need to build JC 2 preamp

Quote:
Originally Posted by ivodonchev View Post
Also can you measure the power consumption of the origial line modul and output dc offset?
According to the photo posted here
Need to build JC 2 preamp
power consumption should be 32mA and offset of this example is 25mV.
Later versions of these modules have a potentiometer to adjust offset.
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Old 11th April 2013, 10:18 AM   #414
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Attachment 341888
Quote:
Originally Posted by pidigi View Post
As Andrew said, the curve Id vs Vgs should be equal in order to consider them matched, and I don't understand if you matched them for Idss, Vgs(off), both or none....

As Andrew already said the two jfets are matched if they have the same curve Id vs Vgs. My jfets are matched for Idss and Vgs.

Measuring the jfets only at Idss are not very accurate because of the heat they are making. I use Idss meassuring only to put them in rough groups(see the picture1). Vgs measuring are more accurate because you can choose a lower working points that you prefer (see the picture2, R3 sets working point). The parts with equal Vgs at two working points (for example at 15mA and 5mA) will have almost identical curve. Remember that measuring should be done at constant room temperature. At picture3 you will see my Jfet matcher, it is ugly but works well.


Regards
Attached Images
File Type: jpg Picture1.jpg (133.7 KB, 428 views)
File Type: jpg Picture2.jpg (293.3 KB, 424 views)
File Type: jpg DSCF5340.JPG (781.3 KB, 412 views)
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Old 11th April 2013, 10:30 AM   #415
AndrewT is offline AndrewT  Scotland
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I think he meant to say that the jFETS are Vgs matched at two Id set points.

Note that diag 1 is not measusing Idss. Vds is ~8.2Vds and varies with each device.
Note that diag 2 has a need for exactly repeatable 10.xyzVdc supply.
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regards Andrew T.
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Old 11th April 2013, 11:47 AM   #416
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Quote:
Originally Posted by AndrewT View Post
I think he meant to say that the jFETS are Vgs matched at two Id set points.

Note that diag 1 is not measusing Idss. Vds is ~8.2Vds and varies with each device.
Note that diag 2 has a need for exactly repeatable 10.xyzVdc supply.
You're right of course,

The voltage drop across the resistor must be taken into account. But for roughly grouping will do the job.

Thanks for the correction
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Old 11th April 2013, 12:07 PM   #417
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Quote:
Originally Posted by gk7 View Post
According to the photo posted here
Need to build JC 2 preamp
power consumption should be 32mA and offset of this example is 25mV.
Later versions of these modules have a potentiometer to adjust offset.
Georg,

You have original modul which is great advanage. Your line modul is with two potentiometers - right? It is important to know do you have any DC offset?

By the way the power supply problem was resolved

Regards
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File Type: jpg DSCF5344.JPG (768.6 KB, 371 views)
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Old 12th April 2013, 01:07 PM   #418
pidigi is offline pidigi  Italy
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Quote:
Originally Posted by ivodonchev View Post
Attachment 341888


As Andrew already said the two jfets are matched if they have the same curve Id vs Vgs. My jfets are matched for Idss and Vgs.

Measuring the jfets only at Idss are not very accurate because of the heat they are making. I use Idss meassuring only to put them in rough groups(see the picture1). Vgs measuring are more accurate because you can choose a lower working points that you prefer (see the picture2, R3 sets working point). The parts with equal Vgs at two working points (for example at 15mA and 5mA) will have almost identical curve. Remember that measuring should be done at constant room temperature. At picture3 you will see my Jfet matcher, it is ugly but works well.


Regards

Thank you ivodonchev, now it is clear. I have infact noticed that the Idss measurement changes with time after the voltage switch on, due to the heating of the fet. For this reason I take the measurement just after few seconds from the start.
Ciao
Paolo
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Old 19th April 2013, 04:17 PM   #419
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gk7, I have a question for you, if you don't mind..

This line stage schematic you've posted some time ago - transistor types aside, does it represent what was in original module or are there any additions/omissins by you?
Particulary, I'd like to know whether C1; C2; C3; C4 and R6; R7; R8; R9 were inside it.
I have a ML schematic that also shows ULD-4 module and I'd like to understand how all internal and external parts interract.

Thanks!
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Old 19th April 2013, 10:58 PM   #420
gk7 is offline gk7
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Location: Vienna, Austria
My schematic (and what I built and use, as described here in this thread) is based on
the schematic of John published. What is inside the modules I donīt know they are
potted with epoxy:
http://www.hal9000.at/audio/JC-2/ml1...00114_jpg.jpeg

R8, R9, R10 are not present in Johns schematic, but my original modules obviously have
a second pot for offset adjustment so I "borrowed" this from the ML-2 power amplifier
which uses the same topology as input stage. It works well.

R6 is only needed if you use that 2u cap in the feedback loop:
http://www.diyaudio.com/forums/attac...ml-1_main2.jpg
itīs the feedback path for DC and certainly must be present in the original modules.

C1; C2; C3; C4 are in the original schematic.

Quote:
Originally Posted by elektroj View Post
...
I have a ML schematic that also shows ULD-4 module ...
Please post it, Iīm curious to see it.
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