Differential probe

[GGMM]

Hello,
Good morning,
I’m thinking about making a differential probe.
Since I have BF988S in advance, I’d like to use them.
However, I would like to know the function of the 5 transistors on this diagram. It's similar and does not exist on the D.Kramniks probe.
 It is not to light a led. LOL
Another modification, I want to find another op amp for the output, to gain bandwidth.
your opinions
cdt

[GGMM]

other pictures

[mk_]

I want to find another op amp for the output

Search TI`s collection of opamps and related parts

other pictures

Kramniks Design is "only" AC

[tggzzz]

However, I would like to know the function of the 5 transistors on this diagram. It's similar and does not exist on the D.Kramniks probe.

They are a current source for the differential amp above your red outline.

The LED and Q2 form a temperature compensated current source, with the current (~150µA) coming out of Q2 collector.

U2A and Q20 form a basic 2:1 current mirror, and Q1 "turns" that into a Wilson current mirror with the current (~300µA) coming out of Q1 collector. Both are described in wackypedia.

[moffy]

The red section is a PNP current source using Q2 and the LED as a temperature tracking reference. The three transistors from the LM3046 and Q1 form a current mirror with I think twice the current going out as is coming in. The current mirror requires very little voltage drop, basically 2Vbes to operate, so it allows the input stage to operate over a wider voltage range.

[GGMM]

Hello,

Thank you for your answers.
So actually the diode is not a gadget. Lol
I put the link for the explaination
cdt

https://en.wikipedia.org/wiki/Wilson_current_mirror

[GGMM]

Hello MK_

I’m more inspired by that.

https://www.diyaudio.com/community/threads/differential-probe-reverese-engineered.248505/

Can you tell me if the DC passes, or possibly what changes need to be made.
Also the fets will be replaced by BF998 (As explained, for a few euros you have more than 10)
So surely modify some resistor
Schematic will be a lot of inspiration of the 2 design

cdt

[tggzzz]

I’m thinking about making a differential probe.

You are considering how it works.

As it is a high voltage differential probe you will also need to consider how it fails. That should include:

• appropriate PCB layout, material, and shape (possibly including slots/cutouts)
• appropriate resistor types; some are more suitable for HV operation and others
• ditto capacitors

https://www.diyaudio.com/community/threads/differential-probe-reverese-engineered.248505/post-3765125

[daisizhou]

https://www.eevblog.com/forum/projects/high-voltage-differential-probe-design-for-review/?nowap
The bandwidth here is 50M, good plan

[mk_]

Hello MK_

I’m more inspired by that.

what kind of diffprobe you need/want to build? a fast one, low voltage or a slower one with hV?

[GGMM]

Re,

Do you have an explanation that on the Kramniks version 2 probe, we went from +/-5V to +/-3.3V to power the op amp?
This implies a circuitry with converter and 2 additional regulator.

why?

cdt

[mk_]

Re,

Do you have an explanation that on the Kramniks version 2 probe, we went from +/-5V to +/-3.3V to power the op amp?
This implies a circuitry with converter and 2 additional regulator.

Yes, but if it is needed... then it has to be done, whats the problem?

why?

I have no idea why Kramnik he decided to go that way.
I design my own probes for max. outputvoltage and therefore I generate the supplyvoltages as needed by the design.

[GGMM]

Re,

it's good.
You have to read the article to the end.
He had too much noise on the power supplies

https://xellers.wordpress.com/electronics/1ghz-active-differential-probe/

cdt

[daisizhou]

Hello,
Good morning,
I’m thinking about making a differential probe.
Since I have BF988S in advance, I’d like to use them.
However, I would like to know the function of the 5 transistors on this diagram. It's similar and does not exist on the D.Kramniks probe.
 It is not to light a led. LOL
Another modification, I want to find another op amp for the output, to gain bandwidth.
your opinions
cdt

Looking forward to sharing it after your success