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NJFETs for Source Follower Applications
NJFETs for Source Follower Applications
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Old 26th October 2018, 12:14 AM   #21
scott wurcer is offline scott wurcer  United States
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One point, anyone could play with this using one of the in-amps like the SSM 2219 or THAT 1512 at g = 100 connected from input to output. Offset, gain, and HD could be measured with almost any sound card.
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Old 26th October 2018, 06:32 AM   #22
EUVL is offline EUVL  Europe
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Or AD8429.


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Old 12th July 2019, 05:07 PM   #23
Oneminde is offline Oneminde  Sweden
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Out of curiosity, why was 2Sk209GR tested and not 2Sk209BL ?


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Old 12th July 2019, 05:40 PM   #24
Nelson Pass is offline Nelson Pass  United States
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NJFETs for Source Follower Applications
Quote:
Originally Posted by EUVL View Post
Post #1, "Each of the N-JFET pairs used in the testing was matched to <10μA in Idss."
So DC was < 1mV in all cases.

But yes, if one can measure upfront and use the JFET with higher Idss for the CCS, a small source resistor will allow easy trimming of DC offset.
I normally do not use source resistor for the upper JFET.
Somewhere I read before it is supposed to create more H3.

2SK117 can still be bought, 2SK209 for sure.
So no need to be desperate, for now at least.
I have been working with J113's in an effort to get good results with
cheap and available parts, and I continue to make some progress.

I have a follower and CCS operated 6 to 12 mA, and with part selection
by Vp and appropriate Source resistors I am currently getting less than .002%
at 1V (-94 dB). If the devices are matched Vp, then equal value Source
resistors on both Fets gives consistently good results.

It gets better with a little more supply voltage, as high as +/-15V.

Of course, the part is too noisy for the input of an MC phono stage...

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Old 12th July 2019, 05:57 PM   #25
EUVL is offline EUVL  Europe
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> Out of curiosity, why was 2Sk209GR tested and not 2Sk209BL ?

2SK209BL is not stocked at Mouser and Digikey.
And at Idss, it is rather limited on Vds due to dissipation.
The idea is to use 2x 209GR in parallel to replace 170BL.


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Old 12th July 2019, 05:58 PM   #26
EUVL is offline EUVL  Europe
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> I have been working with J113's in an effort to get good results

If I am not wrong, your J113 circuit has a DC offset requiring output coupling caps ?


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Old 12th July 2019, 05:58 PM   #27
Oneminde is offline Oneminde  Sweden
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Quote:
Originally Posted by EUVL View Post
> Out of curiosity, why was 2Sk209GR tested and not 2Sk209BL ?

2SK209BL is not stocked at Mouser and Digikey.
And at Idss, it is rather limited on Vds due to dissipation.
The idea is to use 2x 209GR in parallel to replace 170BL.


Patrick
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Old 12th July 2019, 09:22 PM   #28
Nelson Pass is offline Nelson Pass  United States
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NJFETs for Source Follower Applications
Quote:
Originally Posted by EUVL View Post
> I have been working with J113's in an effort to get good results

If I am not wrong, your J113 circuit has a DC offset requiring output coupling caps ? Patrick
Not necessarily. If you match Jfets and Source resistors then the DC
offset is quite low and can be adjusted by resistor trim.
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Old 13th July 2019, 11:51 AM   #29
enochRoot is offline enochRoot  United States
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Is part of the choice of J113 the fact that it's available in TO-92 to make it more DIY friendly for most people vs parts that are only available as SMD?


Quote:
Originally Posted by Nelson Pass View Post
I have been working with J113's in an effort to get good results with
cheap and available parts, and I continue to make some progress.

I have a follower and CCS operated 6 to 12 mA, and with part selection
by Vp and appropriate Source resistors I am currently getting less than .002%
at 1V (-94 dB). If the devices are matched Vp, then equal value Source
resistors on both Fets gives consistently good results.

It gets better with a little more supply voltage, as high as +/-15V.

Of course, the part is too noisy for the input of an MC phono stage...

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Old 13th July 2019, 04:53 PM   #30
Nelson Pass is offline Nelson Pass  United States
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NJFETs for Source Follower Applications
Yes. But also it's cheap and available.
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