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Differential Probe - Reverese Engineered
Differential Probe - Reverese Engineered
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Old 22nd April 2016, 04:57 PM   #21
bading is online now bading  Italy
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Join Date: Mar 2015
Location: Italy
The ground circled in red are the same or the ground of the high voltage signal is isolated ?


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Old 25th April 2016, 09:31 AM   #22
underwurlde is offline underwurlde  United Kingdom
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Location: S.England
Is the same (common) ground.
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Old 28th July 2016, 09:04 AM   #23
Mauby is offline Mauby
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Join Date: Jul 2016
Nice work!

I would like to build 4 of these for my works at home.

Do you have some pictures from the pcb, so that i could get an idea of the design ?
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Old 12th October 2016, 01:38 PM   #24
COSMOS2K is offline COSMOS2K
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Join Date: Jun 2016
Excellent project and excellent reverse engineering.

Thanks for sharing.

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Old 12th February 2017, 10:36 PM   #25
Armadillo is offline Armadillo
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Join Date: Oct 2014
Anyone has the BLM700 datasheet?
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Old 14th February 2017, 02:26 PM   #26
Calvin is offline Calvin  Germany
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Join Date: Nov 2004
Location: close to Basel

heres an interesting DIY build of a Diff-Probe:
click here

My Website
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Old 7th April 2017, 06:20 PM   #27
engenius is offline engenius
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Join Date: Apr 2017
Default U3 substitutes and spares

first of all Id like to thank underwurld for sharing his work results.
I just bricked my SI-9000 (THT version) by accidently applying 30V revers voltage to the output when calibrating it :-(
The output buffer OP amp (U3) had gone. As the code had been sanded off and the part has quite some demanding specs, a suited spare wasnt easy to find.
Some types mentioned in this forum (AD797, etc.) wont probably work, because they use V+ instead of V- referenced offset adjustment.

After spending some time investigating, I figured out these typed:


All of these have at least 25 MHz bandwidth, 300V/s slewrate and low noise. I will give the LT1360 a try because its availability and price (about 4 EUR/1) and its excellent specs.

In the meanwhile, I run the SI-9000 with a TL081 (crappy 100 kHz bandwidth)
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Old 10th April 2017, 09:42 PM   #28
emocabras is offline emocabras
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Join Date: Apr 2017
Hello I write from Italy, you very good great job reverse engineering.

probe power supply be your creation or integrated probe?

I can feed with different dual power supply 9v battery 500mah

resistors marked point have tolerance 1%?

What power Watts have resistances this circuit?

You can publish original probe picture layout component
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Old 25th July 2017, 07:34 PM   #29
Coyote973 is offline Coyote973
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Join Date: Jul 2017
@underwurlde : Great post!

Perhaps adding a photo of other PCB side and how compensating capacitor are arranged (under resistor divider) would make even more clearer (if your device is still apart).

I took a look on schematics SMD type, but I think that R40 is somehow positioned in wrong way. I have searched many current mirrors, Wilson, Widlar,...any current mirror that exists, and haven't found any such mirror that has a resistor in that place.

The listed components are quite old and difficult to find. The U441 is now produced by Linear Systems. I wish I could understand the principles of the weird pair jfet + bjt.
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Old 26th July 2017, 08:27 AM   #30
AndrewT is offline AndrewT  Scotland
Join Date: Jul 2004
Location: Scottish Borders
Can you attach your pics now lost from posts 1 & 2?
regards Andrew T.
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