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Old 18th December 2012, 08:47 PM   #1221
RNMarsh is offline RNMarsh  United States
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And, EXCELLENT Davada, too !
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Old 18th December 2012, 08:50 PM   #1222
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Kudos to both of you! I have only a humble 'stock' unit at the moment, and it works pretty well (for my purposes) with signal averaging, source integrating, and FFT added. However, I AM tempted to make it better.
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Old 18th December 2012, 08:52 PM   #1223
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Default AN73-1

Quote:
Originally Posted by john curl View Post
Has anyone read the Siliconix app note
AN73-1? It is: 'FET's as Voltage-Controlled Resistors' Lots of examples of FET linearization. Anti-parallel, anti-series, feedback, ...
Probably.. once apon a time. I have an old Siliconix manual... I can look at that again too. Will have to review it now for this issue. thx John for the help. -RNMarsh
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Old 18th December 2012, 11:35 PM   #1224
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I can't find that note on the web. This one is newer from the same source and available: http://www.datasheetcatalog.org/data...shay/70598.pdf maybe John can tell us what is missing if anything.

The opamp trick around the fet seems to do what Fig.7 in this note suggests.
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Old 18th December 2012, 11:35 PM   #1225
davada is offline davada  Canada
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Thanks John.

It will be interesting to see if we can get the same performance from every stock 339a with these mods. I do think oscillator, notch, averaging and FFT is the way to go.

Good luck.

Cheers,
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Old 19th December 2012, 03:07 AM   #1226
davada is offline davada  Canada
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This is with two VCR2N in parallel.
The 5th and 3rd came down a bit.
This worsened the 10KHz. It would need to be trimmed separately.
It's almost to the point of having to trim each frequency for best.
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Old 19th December 2012, 03:43 AM   #1227
davada is offline davada  Canada
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Here is 10KHz with a lot of tweaking.

Capacitor in back in on feedback of paralleled Jfets.
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Old 19th December 2012, 05:14 AM   #1228
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by davada View Post
This is with two VCR2N in parallel.
The 5th and 3rd came down a bit.
This worsened the 10KHz. It would need to be trimmed separately.
It's almost to the point of having to trim each frequency for best.
Next up -- 2- VCR2N in parallel and a trim in series with jFEts' source for nulling the H2. Thx-RNMarsh
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Old 19th December 2012, 01:24 PM   #1229
davada is offline davada  Canada
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Quote:
Originally Posted by RNMarsh View Post
Next up -- 2- VCR2N in parallel and a trim in series with jFEts' source for nulling the H2. Thx-RNMarsh
I was thinking of trying this last night but didn't what to cut a trace.

Let me know how this works.
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Old 19th December 2012, 04:38 PM   #1230
RNMarsh is offline RNMarsh  United States
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Default No Fear !

Chicken ! I dont have those same devices but I think I might have some J111 if they are same/similar? I'm not sqeemish about cutting a trace - isnt a problem for me. I dont faint at the sight of a cut. Have No Fear. -RNMarsh
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