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Old 22nd July 2007, 12:34 AM   #1
AuroraB is offline AuroraB  Norway
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Default Ono JFET matching

I'm finally getting around to finish the two Onos I started a couple of years ago. Got severly delayed , for several reasons..
I was measuring my way around 100+ of 2SK170GRs for the MC section, and the main questions is simple-- two what tolerances are you guys mathing these JFETs???

I got some very good quads out of this, in the range of 50-65 mV across the 22 ohm resistor.

I remember NP said something about these tolerances, but when I started searching I couldn't find it- what I did find, though, was a statement from NP that they used the BL version...???
In all the older treads "everybody" is looking for GR - which I have, and stating that the BL will cause the MC cascode to malfunction..??

What did I miss here, if anything???
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Old 23rd July 2007, 08:31 AM   #2
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Hi,

I have build the ono with BL types. and matched the Id current against a Ugs of 0V within 0,1mA.
In the running versions, the drain current is within 0,5mA and that is sufficient for correct operation of the frontend.

I wonder if you would let me buy some of your GR types, as I modified the drain resistors and the source resistor to controll the current with the BL types in the frontend, as well as used a 400E drain resistor instead of 1K (to have sufficiend voltage reserve).
Also the output fet of the frontend is not working well with the BL type.

So I would be very interested to buy some of your GR types.
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Old 23rd July 2007, 01:31 PM   #3
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AuroraB:

I started out with 80 2SK389BL and managed two quads that have a total current draw of less than 10mA. It is my understanding that the BL are preferable when you can achieve this. If not, then use the GR grade. Here are my final, in-circuit measurements:

Idss for 2sk170gr
=============
Q_13_R = 2.35 mA
Q_12_R = 2.32 mA
Q_11_R = 2.27 mA
Q_10_R = 2.22 mA

Q_13_L = 2.54 mA
Q_12_L = 2.46 mA
Q_11_L = 2.47 mA
Q_10_L = 2.47 mA

I would reference Algar_emi's schematics as he gives node voltages for both types and has excerpts of posts in the download that discuss this somewhat.

Take care!
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Old 23rd July 2007, 04:06 PM   #4
MRupp is offline MRupp  Germany
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Better still get the Borbely articles on JFETs and/or the Siliconix application notes on JFET bias, and the datasheets of the 2SK170, and then figure out for yourself.
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Old 23rd July 2007, 06:02 PM   #5
AuroraB is offline AuroraB  Norway
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Well, - I have all the Borbely articles....
Point is, that the GR version is the one with the lowest Idss - not the BL. If the total current of all four is supposed to stay at or below 10mA, the BL cannot be used easily. That's why I wonder about the conflicting messages.
I have managed to get 6-7 good quads out of my 100+, but since I'm building two simultaneously (one for my brother), I think I need the extra sets as spares, but I'll do another test setup.
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Old 23rd July 2007, 06:04 PM   #6
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Quote:
Originally posted by AuroraB
the BL cannot be used easily. [/B]
exactly my rationale. Use the GR.
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Old 23rd July 2007, 11:37 PM   #7
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The Onos use BL types. As they measure Idss at
the low end of the spec range, it has not created
any difficulties.


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Old 24th July 2007, 11:05 AM   #8
AuroraB is offline AuroraB  Norway
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Thanks alot, Mr. Pass, for clearing this up.
I figured this was the case, but if 2.5mA is the designed current level for the JFETs, the yield out af a BL batch must be quite low.
Some have reported voltages across the source resistor in the order of 70-100 mV, indicating currents in the order of 4 mA +/-, not 2.5.
It would be clarifying to know the designed level ( and also for the Pearl...)

Moderators-
For some time I've seen the necessity of some sticky fact sheets, also for others of the more popular projects. I know there are Wikis for some pfrojects, but what about some sort of "Design Facts" section ??
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Old 24th July 2007, 04:31 PM   #9
MRupp is offline MRupp  Germany
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Quote:
Here are my final, in-circuit measurements:
I don't think the JFets need to be that closely matched to each other in this position. Instead I would generally match components channel to channel so that the values are as close as possible. For your JFets this would mean swapping two of them from L to R so that your total current draw is about the same (right now it is 10% off, maybe not a big deal but if you want to be accurate be accurate where it makes sense).
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Old 25th July 2007, 11:12 PM   #10
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Default Thank-you for clearing that up, Nelson

Quote:
The Onos use BL types ... Nelson Pass
Dear Nelson,

Thank-you for the final word on the type of Jfet you used for the Ono. I have watched the Ono/Xono threads for a long time and have seen grown men have apoplexy because they could NOT get the GR versions! - all they could ever find was those "dreadful" BL's

It is nice to be put at ease.

Regards,
George.
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