Where can I find inexpensive differential probes?

[nbritton]

Where can I find inexpensive differential probes? I have a four channel scope and I'd like to probe across four individual components in circuit so that I can study their properties for educational purposes. I don't need anything fancy or high voltage or high bandwidth.

[eas]

Definite inexpensive.

As I recall from previous threads, its hard to get under $200/channel.

[BravoV]

Nothing fancy, no high voltage, no high bandwidth and for educational, why not use two probes with both ground alligator clips connected together, and use both tips for differential probing.

Of course, this technique has limitation and you should aware of it.

[nbritton]

Nothing fancy, no high voltage, no high bandwidth and for educational, why not use two probes with both ground alligator clips connected together, and use both tips for differential probing.

Of course, this technique has limitation and you should aware of it.

Using the A-B differential probing method would limit me to two channels.

[nbritton]

Definite inexpensive.

As I recall from previous threads, its hard to get under $200/channel.

Shooting for $50 a probe. They can be 1 MHz probes for all I care, my main goal is just to get 4 differential channels. If I need to do high speed probing I can use conventional methods.

[nowlan]

I think pintek is as good you will find. Still not cheap enough for me.

[nidlaX]

Definite inexpensive.

As I recall from previous threads, its hard to get under $200/channel.

Shooting for $50 a probe. They can be 1 MHz probes for all I care, my main goal is just to get 4 differential channels. If I need to do high speed probing I can use conventional methods.

I just made a search recently and found nothing below the ~$170 range in all the usual places. If you're interested in DIY, this write up might give you some ideas: https://xellers.wordpress.com/electronics/1ghz-active-differential-probe/

EDIT: On second thought, I'm not sure if this is what you're looking for. There have been a few projects on this forum researching DIY, low cost differential probes with modest bandwidth. Not sure if any of them have iterated to completion though.

[Pinkus]

I purchased a 20 Mhz, 450 Vpp 100:1 / 10:1 differential probe on ebay a year ago.
I barely used it as I needed higher voltage and purchased a (expensive) Pintek DP100 (6500V, 100 Mhz) differential probe later, which I am now using - so I can and will sell the other differential probe.

The seller buildt it by himself, the schematic and PCB is based on an article in an Elektor magazine. It comes calibrated and in a housing including a buildt-in power supply and is nicely shielded internally. The full (english) article from Elektor including schematics is available. I will sell for the price I purchased it for which is pretty attractive:  Price will be 75 Euros including shipping in Europe for payments via bank transfer. Paypal is possible but will add 3% paypal fee.

Non Europe countries: I can ship to other parts of the world too, probably ~ 10 Euro more for the shipping costs (I have to check first). But you should know that the buildt-in power supply is for 220-240V AV. For 110V you either need to change the internal transformer (2x 15V 3VA) or you will need to connect the supply voltage from an external source.

If interested, please send a PM, I can provide addl. information (pictures, scope pictures etc.) then.

[nbritton]

That's a shame that there are no cheap probes. What probes are compatible with extra pins on the Rigol DS4000 series scope?

[nbritton]

I don't understand why these things are so expensive, isn't it just a few opamps inside them?

[fpliuzzi]

I'll have to leave the question about what probes are compatible with the extra pins on the Rigol DS4000 series scope to others. I haven't personally used the following differential probe, but some forum members may find that it would suit their present needs if their requirements are somewhat modest.

I came across the $79.00 'QuantAsylum' differential probe about a year ago. If I didn't already own a LeCroy AP031 differential probe at that point I probably could have lived with its CAT I 150Vrms (800V momentary surge) and 4MHz bandwidth limitations since I mostly work on audio circuits.

The following page has lots of technical data about the probe's performance.

www.quantasylum.com/content/Products/QA190.aspx

Also, the "low distortion, low noise" differential probe (their words) has an AC current clamp feature built-in (15A max), plus a 15 day money back quarantee.

NOTE: Their spec sheet states that the max input voltage is 150Vrms or +/-150V DC.
Derate by 70% per decade over 50KHz (eg 500KHz max voltage is 0.3 x 150 = 45Vrms).

[pakesson]

Here's one you can build yourself fairly cheaply, https://github.com/newaetech/chipwhisperer/tree/master/hardware/tools/diffprobe. I'm not sure about the actual performance, but it's based on the AD8129 (http://www.analog.com/media/en/technical-documentation/data-sheets/AD8129_8130.pdf) which is a 270 MHz differential amplifier. Maybe good enough for (low voltage) hobby stuff?

You can also buy it as a blank pcb (http://store.newae.com/differential-probe-blank-pcb/) or assembled and tested (http://store.newae.com/differential-probe-assembled-tested/) if you want to save some time.

It's designed by Colin O'Flynn (the ChipWhisperer guy), and some more documentation can be found on the ChipWhisperer wiki at http://newae.com/sidechannel/cwdocs/naecw501_hwdiffprobe.html.

(I have one on the pre-assembled ones, but I haven't tested it yet)

[commongrounder]

That's a shame that there are no cheap probes. What probes are compatible with extra pins on the Rigol DS4000 series scope?

Rigol makes a series of compatible active current and voltage probes for the DS4000/6000 scopes.  There is one adaptor that allows certain Tektronix active probes to be used on the scopes.  All of these are listed on the RigolNA web site under "Accessories".  And all are pricey!

[tautech]

I don't understand why these things are so expensive, isn't it just a few opamps inside them?

Full isolation would be the best solution but alas few scopes come with it.

Consider this:
http://www.siglentamerica.com/prodcut-fjxx.aspx?fjid=404&id=27&tid=1&T=2

Recent thread:
https://www.eevblog.com/forum/testgear/siglent-isfe-scope-front-end-isolator-any-opinions/

[nctnico]

Siglent's ISFE looks like a good buy if you are not after high frequencies. Add a simple 1:1 probe and you are all set (like the dirt cheap Hantek PP80 which has isolated BNCs).

[Mechatrommer]

I don't understand why these things are so expensive, isn't it just a few opamps inside them?

Full isolation...

why add injury to the insult?

I don't understand why these things are so expensive, isn't it just a few opamps inside them?

and hours of labours work... if you can mitigate it to yourself then yes, its just a few opamps, passives, a pcb and an enclosure+probes cabling...

[tautech]

I don't understand why these things are so expensive, isn't it just a few opamps inside them?

Full isolation...

why add injury to the insult?

 

[nbritton]

Here's one you can build yourself fairly cheaply, https://github.com/newaetech/chipwhisperer/tree/master/hardware/tools/diffprobe. I'm not sure about the actual performance, but it's based on the AD8129 (http://www.analog.com/media/en/technical-documentation/data-sheets/AD8129_8130.pdf) which is a 270 MHz differential amplifier. Maybe good enough for (low voltage) hobby stuff?

You can also buy it as a blank pcb (http://store.newae.com/differential-probe-blank-pcb/) or assembled and tested (http://store.newae.com/differential-probe-assembled-tested/) if you want to save some time.

It's designed by Colin O'Flynn (the ChipWhisperer guy), and some more documentation can be found on the ChipWhisperer wiki at http://newae.com/sidechannel/cwdocs/naecw501_hwdiffprobe.html.

(I have one on the pre-assembled ones, but I haven't tested it yet)

Not exactly a flat response. There is a cliff between DC and 2 MHz, then in the middle there is a over 6dB of gain. I don't think I could make reliable measurements with this device, I was hopping for a maximally flat response from DC to x MHz.

[nbritton]

Would a balun work? Doesn't that take a differential pair and convert it via a transformer to a single ended connection?

http://www.amazon.com/Channel-Video-BNC-RJ45-Balun/dp/B0056KLG52

The problem with regular probes is their ground is all bonded to the same point, so if you hooked them up to different points in the circuit you would short out the circuit. If you had a balun transformer wouldn't that technically isolate the channels? Although wouldn't that short out the component your testing unless you put the balun in series. hmm. Why does this stuff have to be so expensive, maybe I should find a cheaper hobby.

[nbritton]

That's a shame that there are no cheap probes. What probes are compatible with extra pins on the Rigol DS4000 series scope?

Rigol makes a series of compatible active current and voltage probes for the DS4000/6000 scopes.  There is one adaptor that allows certain Tektronix active probes to be used on the scopes.  All of these are listed on the RigolNA web site under "Accessories".  And all are pricey!

Rigol wants $2k for their RP7080 probe! That's almost as much as I paid for the scope, and here I thought the scope would be my biggest purchase cost, nope, it's the damn probes.

[nbritton]

I don't understand why these things are so expensive, isn't it just a few opamps inside them?

Full isolation would be the best solution but alas few scopes come with it.

Consider this:
http://www.siglentamerica.com/prodcut-fjxx.aspx?fjid=404&id=27&tid=1&T=2

Recent thread:
https://www.eevblog.com/forum/testgear/siglent-isfe-scope-front-end-isolator-any-opinions/

That looks cool except for the fact that it has Siglents name on it. Are there any other isolators that are not made by Siglent?

[tautech]

That's a shame that there are no cheap probes. What probes are compatible with extra pins on the Rigol DS4000 series scope?

Rigol makes a series of compatible active current and voltage probes for the DS4000/6000 scopes.  There is one adaptor that allows certain Tektronix active probes to be used on the scopes.  All of these are listed on the RigolNA web site under "Accessories".  And all are pricey!

Rigol wants $2k for their RP7080 probe! That's almost as much as I paid for the scope, and here I thought the scope would be my biggest purchase cost, nope, it's the damn probes.

Yep.

[tautech]

I don't understand why these things are so expensive, isn't it just a few opamps inside them?

Full isolation would be the best solution but alas few scopes come with it.

Consider this:
http://www.siglentamerica.com/prodcut-fjxx.aspx?fjid=404&id=27&tid=1&T=2

Recent thread:
https://www.eevblog.com/forum/testgear/siglent-isfe-scope-front-end-isolator-any-opinions/

Are there any other isolators that are not made by Siglent?

Not that I'm aware of, they are a simple elegant well priced solution.
As I've mentioned in the ISFE tread you'll need to check your scopes input BNC spacings for a then very simple installation.
Also ensure you have 200:1 attenuation for the input settings.

That looks cool except for the fact that it has Siglents name on it.

Can you swallow your pride?

[nbritton]

I'll have to leave the question about what probes are compatible with the extra pins on the Rigol DS4000 series scope to others. I haven't personally used the following differential probe, but some forum members may find that it would suit their present needs if their requirements are somewhat modest.

I came across the $79.00 'QuantAsylum' differential probe about a year ago. If I didn't already own a LeCroy AP031 differential probe at that point I probably could have lived with its CAT I 150Vrms (800V momentary surge) and 4MHz bandwidth limitations since I mostly work on audio circuits.

The following page has lots of technical data about the probe's performance.

www.quantasylum.com/content/Products/QA190.aspx

Also, the "low distortion, low noise" differential probe (their words) has an AC current clamp feature built-in (15A max), plus a 15 day money back quarantee.

NOTE: Their spec sheet states that the max input voltage is 150Vrms or +/-150V DC.
Derate by 70% per decade over 50KHz (eg 500KHz max voltage is 0.3 x 150 = 45Vrms).

I'm not sure this will work, I'm confused, at the bottom of their spec sheet it says their probe isn't isolated. Isn't isolated inputs implied on a differential probe? The whole reason I'm looking at differential probes is because I need isolated channels. right? Or are they talking about a different kind of isolation?

[forrestc]

Where can I find inexpensive differential probes? I have a four channel scope and I'd like to probe across four individual components in circuit so that I can study their properties for educational purposes. I don't need anything fancy or high voltage or high bandwidth.

FYI, The problem seems to be that 'differential' often seems to be equated to 'isolated'.   Differential = fairly cheap (aka low vos opamp and some passives), isolated = expensive (think about moving a high accuracy signal across a isolation barrier).

It sounds like you want differential instead of isolated.  In the past I've just used a relatively low offset rail to rail quad opamp configured as a instrumentation amplifier.  $1 on a breadboard.

I like the looks of the AD8129/AD8130 used by the chip whisperer differential probe linked to by someone else.  I might get a couple for future use.

[forrestc]

I'm not sure this will work, I'm confused, at the bottom of their spec sheet it says their probe isn't isolated. Isn't isolated inputs implied on a differential probe? The whole reason I'm looking at differential probes is because I need isolated channels. right? Or are they talking about a different kind of isolation?

You may or may not need a isolated probe.

In my applications, usually everything is ground referenced, and the voltages are often relatively low on board.   When I need a 'differential probe', I usually just need to reference a measurement from a different potential than ground.   For instance, measuring the high-side current in a circuit which is ground referenced.   

Let's assume your circuit is ground referenced (or could be), and uses a relatively low operation voltage (say around 3.3V).  In this case, you could just use an opamp/instrument amp to measure the voltage across the components of interest.

[nbritton]

Are there any other isolators that are not made by Siglent?

Not that I'm aware of, they are a simple elegant well priced solution.
As I've mentioned in the ISFE tread you'll need to check your scopes input BNC spacings for a then very simple installation.
Also ensure you have 200:1 attenuation for the input settings.

That looks cool except for the fact that it has Siglents name on it.

Can you swallow your pride?

I suppose so if there are no other reasonable solutions. I do have 200:1 attenuation on my scope, although the physical spacing isn't right so I would have to get BNC extention cables.

[oldway]

http://thetooth.name/dev/UK2010090601.pdf

There is also a differential probe project with AD830AN in Elektuur 04/1994, but I can't post the schematic here because of copyright problems.

[nbritton]

I'm not sure this will work, I'm confused, at the bottom of their spec sheet it says their probe isn't isolated. Isn't isolated inputs implied on a differential probe? The whole reason I'm looking at differential probes is because I need isolated channels. right? Or are they talking about a different kind of isolation?

You may or may not need a isolated probe.

In my applications, usually everything is ground referenced, and the voltages are often relatively low on board.   When I need a 'differential probe', I usually just need to reference a measurement from a different potential than ground.   For instance, measuring the high-side current in a circuit which is ground referenced.   

Let's assume your circuit is ground referenced (or could be), and uses a relatively low operation voltage (say around 3.3V).  In this case, you could just use an opamp/instrument amp to measure the voltage across the components of interest.

I like the QuantAsylum QA190, but it's my understanding the probe isn't isolated. The trouble with scopes is that all the grounds are bonded together, if I were to connect the probes across different points in the circuit I would short out the circuit. So I was thinking that a differential probe would solve that problem because they offer isolation, but now I'm confused about what I actually need. Lets keep this simple, lets say I want to measure the voltage drop across four resistors in a circuit on my scope, what product do I need?

[forrestc]

I like the QuantAsylum QA190, but it's my understanding the probe isn't isolated. The trouble with scopes is that all the grounds are bonded together, if I were to connect the probes across different points in the circuit I would short out the circuit. So I was thinking that a differential probe would solve that problem because they offer isolation, but now I'm confused about what I actually need. Lets keep this simple, lets say I want to measure the voltage drop across four resistors in a circuit on my scope, what product do I need?

You need four copies of the circuit shown/described at:

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

Or an equivalent circuit with something like the parts referenced in the Wikipedia article.

Note that each input is high-impedance into the opamps/instrument amplifiers.  This means that attaching shouldn't affect your circuit.  The quality of your measurements will depend on the quality of the amplifiers and/or matching of the resistors.   You'll need to make sure you respect the ratings of the opamps and that they are powered/referenced correctly, but that should be all you need.

-forrest

[fpliuzzi]

I'm not sure this will work, I'm confused, at the bottom of their spec sheet it says their probe isn't isolated. Isn't isolated inputs implied on a differential probe?

nbritton you piqued my interest about isolation so I just checked my LeCroy AP031 differential probe. While it was powered-up I measured about 4Mohm from either of its inputs to the ground or the center pin of the BNC on the output of the probe (switching the attenuation from 1/100 to 1/10 had not effect on this value).

The fact that my AP031 isn't fully isolated hasn't stopped me from using the probe in any situation so far.

Regards

-------------------
*Edited for clarity

[eas]

I like the QuantAsylum QA190, but it's my understanding the probe isn't isolated. The trouble with scopes is that all the grounds are bonded together, if I were to connect the probes across different points in the circuit I would short out the circuit. So I was thinking that a differential probe would solve that problem because they offer isolation, but now I'm confused about what I actually need. Lets keep this simple, lets say I want to measure the voltage drop across four resistors in a circuit on my scope, what product do I need?

1MOhm + 1MOhm = a short circuit?  You sure about that?

[Marco]

The trouble with scopes is that all the grounds are bonded together

Ah I see where  you went wrong here, just because you can use scope probes with the QA190 doesn't mean you should use the ground leads. You generally shouldn't, if the circuit floats you could decide to attach one.

Also you should use 1x probes.

Lets keep this simple, lets say I want to measure the voltage drop across four resistors in a circuit on my scope, what product do I need?

If you can live with the bandwidth, noise, CMRR, input resistance and common mode voltage range of the QA190 then it will work for that (most other high voltage differential probes will be poorer for everything except the input resistance and common mode voltage range as explained on their product page).

[nbritton]

I like the QuantAsylum QA190, but it's my understanding the probe isn't isolated. The trouble with scopes is that all the grounds are bonded together, if I were to connect the probes across different points in the circuit I would short out the circuit. So I was thinking that a differential probe would solve that problem because they offer isolation, but now I'm confused about what I actually need. Lets keep this simple, lets say I want to measure the voltage drop across four resistors in a circuit on my scope, what product do I need?

You need four copies of the circuit shown/described at:

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

Or an equivalent circuit with something like the parts referenced in the Wikipedia article.

Note that each input is high-impedance into the opamps/instrument amplifiers.  This means that attaching shouldn't affect your circuit.  The quality of your measurements will depend on the quality of the amplifiers and/or matching of the resistors.   You'll need to make sure you respect the ratings of the opamps and that they are powered/referenced correctly, but that should be all you need.

-forrest

I found this eBook that might be useful:
Analog Devices: A Designer’s Guide to Instrumentation Amplifiers 3rd Edition

Are there any pre-made or kit based instrumentation amplifiers? I think this is what the QuantAsylum QA190 is, from its website it states: "the internals of the QA190 are Jung’s classic “Buffered Input Balanced Line Receiver” from Chapter 6, figure 6-30, of the Analog Devices Op-amp Application Handbook. With some updated opamps, of course."

[forrestc]

I found this eBook that might be useful:
Analog Devices: A Designer’s Guide to Instrumentation Amplifiers 3rd Edition

Are there any pre-made or kit based instrumentation amplifiers? I think this is what the QuantAsylum QA190 is, from its website it states: "the internals of the QA190 are Jung’s classic “Buffered Input Balanced Line Receiver” from Chapter 6, figure 6-30, of the Analog Devices Op-amp Application Handbook. With some updated opamps, of course."

The chipwhisperer CW501 is one (thanks to whoever mentioned it above in this thread)..   not sure if it will work for your application.   http://newae.com/sidechannel/cwdocs/naecw501_hwdiffprobe.html

You should think about the accuracy you really want/need, along with things like frequency response, etc.     

One other reference:   If you have access to the art of electronics, there is some good reference in there for this type of thing.

[Marco]

Do be careful about not using the nulling potmeter on the chipwhisperer, it causes a high pass filter effect.

You can use it as a differential probe, but it's a LOT easier to destroy than the QA190.

[Mechatrommer]

http://en.elektronicastynus.be/projects/7/e

Error 404: Not Found. is it just me or what?
the above picture looks unsafe..

[saelig]

Diff probes aren't cheap - here's ours: http://www.saelig.com/PSBEAV/PSA010.htm  $341.59.  Maybe others can find cheaper ones, but make sure they're safe!

Alan Lowne
CEO
Saelig Co. Inc.

[Pinkus]

http://en.elektronicastynus.be/projects/7/e

Error 404: Not Found. is it just me or what?
the above picture looks unsafe..

just remove the /e at the end.
This works: http://en.elektronicastynus.be/projects/7

[Mechatrommer]

http://en.elektronicastynus.be/projects/7/e

Error 404: Not Found. is it just me or what?
the above picture looks unsafe..

Try:
http://hackedgadgets.com/2012/05/23/differential-probe-project/

my avast reporting INfection: HTML:Script-inf

http://prosje.be/CO/Schemas/slides/DiffProbe.html

ok this works thanks... ok i guess its safe. i thought the mains plug is something directly connected to the top bnc, now i know how the signal flows...

just remove the /e at the end.
This works: http://en.elektronicastynus.be/projects/7

o ok just saw this.. it works thanks.

[cat87]

This question also bugged me for some time. I searched for about a month for a decent priced Differential probe on eBay and let me tell you....anything above 150 Euros is just B.S. The seller is either on drugs or  he's just following the price trend.
I finally scored a nice 1.5KV 25MHz probe for 130 Euros, but after examining it, I think that one can build a probe quite cheaply. Unfortunately, in the end, it has to be  calibrated with a Spectrum Analyzer and a tracking generator, and this is the real issue with building one.
Anyway, for anyone interested in doing the same, I decided I put the information I have in a friendly format: http://electronicsplayground.blogspot.ro/2015/07/high-voltage-differential-probe-design.html

[Mechatrommer]

I think that one can build a probe quite cheaply....

if you are talking about tangible matters, you are right. as a little hint, spectral density or purity is of less interest and/or poses less problem in designing this kind of device, whats bugging are parasitics (leakage or coupling on certain nodes) and CMRR (matching both inputs)

[blackdog]

Hi,

This is probe i designed about 2 years ago...
The LH0002 is old and no longer available but can be replaced by any other rapid buffer 2x 18V or 20V can handle.
This probe was 1: 100 and can supply large signals at the output, to 200kHz 30Volt Top Top.
At 1 MHz this is still 6V Top Top.
This probe is after good adjustment level within 0.5 dB to well above 20Mhz.



The most important measurements are given in the graph below.
At frequencies below 10 kHz are my noise floor and the common mode rejection is better than -75dB there.
The frequency characteristic is shown at 100 mv output voltage.
Be aware that most probe manufacturers give very few specifications of there products.


When properly build and using high quality components you can use this probe to several hundred volts.
For more information and lots of photos of my measurements, you can look at the Dutch Forum "Circuit Online".
It is a fairly extensive topic and in Dutch, you can use "Google Translate" to read it.

http://www.circuitsonline.net/forum/view/118515/1/differential+probe

Kind regarts,
Blackdog

[Marco]

I think that one can build a probe quite cheaply.

If your time is free.

Although even then if you really want something build to CATIII standards you'll probably just buy something like the PICO probe Saelig is selling.

[Marco]

Anyway, for anyone interested in doing the same, I decided I put the information I have in a friendly format: http://electronicsplayground.blogspot.ro/2015/07/high-voltage-differential-probe-design.html

I like these kinds of circuits, they don't depend on resistor matching for CMRR. I fail to see why you would ever use instrumentation opamp circuits instead of these kinds of circuits.

Of course it doesn't remove the problem that at high common mode voltages you'll need resistive dividers first to get the common mode voltage to something it can handle, which reintroduces the resistor matching problem.

PS. why are the collectors of Q5B/C not just connected to the positive rails? Pulling their current through R13/24 just increases the Miller effect AFAICS.

[Mechatrommer]

Anyway, for anyone interested in doing the same, I decided I put the information I have in a friendly format: http://electronicsplayground.blogspot.ro/2015/07/high-voltage-differential-probe-design.html

it doesn't remove the problem that at high common mode voltages you'll need resistive dividers first to get the common mode voltage to something it can handle, which reintroduces the resistor matching problem.

i failed to see the link earlier. there are a bunch of family links down there so i guess cat87 must have done his homework just like me or us his report only up to simulation though, we cant wait for the part II report ... i guess he ran through the matching problem as well?, cant tell exactly why, needs his conformation on this... and btw not to scare everybody... i would like to point out, at lesser bandwidth say 1MHz or so, matching and CMRR problem will be a lot less severe, and building diy one is alot easier... i was just too high of expectation during specifying my design stuffs, so no success so far.... just so for anyone who like to build their own...

[cat87]

PS. why are the collectors of Q5B/C not just connected to the positive rails? Pulling their current through R13/24 just increases the Miller effect AFAICS.

That may be the case, but in the simulations I've run, I get the same result with the collectors connected to Vcc directly or through R13/R24. But I suppose this will be something I'm going to experience once I make the  actual circuit.

[tggzzz]

I haven't read the whole thread, so my apologies if this has been mentioned before.

For some purposes, the homebrew technique mentioned in http://emcesd.com/pdf/cd94scr.pdf (Balanced Probe Extends High-Frequency Measurements) is useful. The article also demonstrates some problems with standard probes.

[Marco]

For some purposes, the homebrew technique mentioned in http://emcesd.com/pdf/cd94scr.pdf (Balanced Probe Extends High-Frequency Measurements) is useful. The article also demonstrates some problems with standard probes.

Instead of the combiner you could also use an AD8129/AD8130 with the passive divider probes, slightly less bandwidth but it would be DC coupled unlike with the combiner.

[Mechatrommer]

For some purposes, the homebrew technique mentioned in http://emcesd.com/pdf/cd94scr.pdf (Balanced Probe Extends High-Frequency Measurements) is useful.

that looks easy, how the 180 degrees shift combiner circuit looks like? that is good for 500MHz?

Instead of the combiner you could also use an AD8129/AD8130 with the passive divider probes, slightly less bandwidth but it would be DC coupled unlike with the combiner.

then it will get back to passive dividers + ins-amp config?

[Marco]

It's not made to work with high voltages any way, the only dividers you'd need are the 10x dividers on the coax inputs.

[leotdi_PL]

The seller buildt it by himself, the schematic and PCB is based on an article in an Elektor magazine.....

Hallo Pinkus,

where can I find a LIST of COMPONENT ?
(Article and PCBs already have!)

thank you 

leotdipl

[oldway]

That's an old topic....

Anyway, you don't need the list of components because all the values of the components are specified on the schematic and you can easily make your own list of components.

[leotdi_PL]

That's an old topic....

Anyway, you don't need the list of components because all the values of the components are specified on the schematic and you can easily make your own list of components.

ok, i understand, but the list defines the parameters of elements (eg. as important as voltage/power).
If someone is able to help me thank you very much, because I am not able to find this list on the Internet.
She is not primarily on elektormagazin.com. Otherwise I would not write here.
Thank you to those who want to HELP 

[oldway]

If it is the differential probe with AD830AJ and AD844AN from elektor, nobody will HELP you 

Because...the list of components has never been published....only the schematic....there are enough informations in the schematic to make the list of components if you need it....

[twentynothing]

You can't beat the price of this one: https://www.amazon.com/Micsig-DP10013-Differential-Attenuation-Tektronix/dp/B074K4XPW3/
It is also a high voltage differential probe.

[David Hess]

Shooting for $50 a probe. They can be 1 MHz probes for all I care, my main goal is just to get 4 differential channels. If I need to do high speed probing I can use conventional methods.

If you only need up to 1 MHz, then there are several integrated instrumentation amplifiers which can be used for good performance.  I would probably start with the AD8421 because it has low bias current inputs and high AC common mode rejection.

The big problem is limited input common mode range.  Compensated resistive dividers can be added to the inputs but they need to be adjusted to maintain common mode rejection.  If high impedance dividers are used, then the printed circuit board substrate becomes a problem; a lot of commercial high voltage differential probes have problems with printed circuit board "hook" making them essentially trash despite their high prices.

I don't understand why these things are so expensive, isn't it just a few opamps inside them?

For high voltage differential probes, the high input impedance dividers on the input make it very difficult to maintain high common mode rejection.  Many commercial high voltage differential probes are junk because of printed circuit board "hook".

Feedback amplifiers made from integrated operational amplifiers have a lot of problems with overload recovery, transient response, and coupling between the inputs (1) so designs using operational amplifiers are cutting edge simply because they are a poor choice for this application.

(1) There is a reason integrated differential pairs are *not* used for high performance differential probes; coupling between the integrated transistors ruins AC common mode rejection.

I finally scored a nice 1.5KV 25MHz probe for 130 Euros, but after examining it, I think that one can build a probe quite cheaply. Unfortunately, in the end, it has to be  calibrated with a Spectrum Analyzer and a tracking generator, and this is the real issue with building one.

Transient response calibration is more difficult and necessary.  It requires a high voltage reference level pulse generators which is a very specialized piece of test equipment.  Any RF signal generator can be used to check for resonance peaks.