The resistor is not for offset, but to maximize the common mode rejection ratio. If one of the 4meg is actually 4meg+1% and the other has 4meg-1% then the CMRR is only 34dB. With the resistor you can tune the CMRR for DC to much higher values.

Shoutout to Mr. Wu!

Hearing the audio change at around 12 minutes really freaked me out. I thought it might be someone doing their best Dave impression, but they captured your mannerisms way too perfectly. Bizzare!

Hi Dave! By watching the video I managed to repair my own Pintek differential probe that I just burned by extremely high discharge from Xenon lamp that I do not expected... I couldn't made it if I do not know the architecture. THANKS from Russia!!!

18:30 A few months ago I was troubleshooting a photomultiplier charge sensitive preamp for my boss and it used an op-amp constructed from individual transistors including a higher-voltage version of the array chip shown off at this timestamp (LM3146). I thought at first that it was the part that died and did some research into sourcing a new one and it turns out that these are a nightmare to find nowadays. Luckily the dead part ended up being a 2N3096 though, but that's something to keep in mind if you have to fix something ancient that uses one of these things - you may not be able to find a proper replacement

Dave, I think it would make a cool video if you tested the performance of this thing. In particular, I'd like to see Bode plots of the common-mode and differential-mode response, and what happens if you overload it. (Do you get a phase reversal?) BTW some of those discrete transistors may be used as clamps to protect the opamp from overloads.

11:38, Dave voicover hangover edition :)

I bought one almost the same from Probe Master, also compatible with LeCroy. All the same features, including 4 Meg inputs and 70/700 V ranges. But mine is 100 MHz. By the way, the 70 V and 700 V reflect the output saturation (from 9.5 V supply rails) of +/- 7 V. The input capacitor arrangement is for frequency compensation. The series string & the 4 Meg resistors form the same time constant as the parallel set with their 25 k resistor. Same idea as used on 10x probe compensations.

In all those years I have been watching the EEVblog I haven´t noticed Dave uses the european resistor symbol. I love it.

Yes, comparing one of those you can get on ebay to this one would be very interesting for many viewers I believe.

For a divider, to be frequency flat, the capacitance in the series vs the capacitance in the shunt part has to be inverse of the divider ratio to have a flat frequency response (the math on this is your homework). In this case, 160. (4M/25k) . 6,8/3=2,27pF in the series branch (to dominate the paracitics of the resistors) 120 + 82 +82 *x =284+x . x is the trimpot. 160*2,27=363,2pF, so the trimpot is about 80 pF. This will make a flat frequency response

Why are these probes soo bloody expensive?? doesn't look all that special in there.

I love the way Dave refers to the components as "puppies."

The Caps are additionally isolated due to the fact that the Body of most passive parts are not specified in terms of isolation. This means the certification bodies does not accept it unless you isolate them.

Uhm, did I miss anything or why was the circuit board pixeled out in the thumnail which just changed?

Back for a 2nd suck of the salve. Thank you! (again)

The remained part of logo on dip-14 looks like NTE logo. It could be NTE 987 quad opamp with true differential input. Edit: I think I found the schematic of similar design -i92.photobucket.com/albums/l40/underwurlde666/stuff/DiffProbeSMT.jpg

Great teardown, and after a few years you might have figured it out - but I reckon its using something like THIS - an actual diff vid/instrumentation amp like the NE592 ...

I am not a fan of the scrubbed off part numbers, this shouldn't be a practice in industrial equipment. In my opinion, they don't want it to be reverse engineered and sold at a fraction of the price. Those scrubbed off numbers are an indicator that the price isn't justified.

Maybe Mr. Yolo should start selling a competitive product to Mr. Wu's probe.

Dave, would be cool to do the same with a isolated differential probe, and see how they do the isolation

Would be interesting to hook it up to a sweep generator, once as a common mode input and once in differential mode to see how good it is.

Awesome video!

Do you think the switch effects its 10x/100x change by changing the current in the current source? Those extra trim pots might be for adjustments there

Mr Wu did some funky soldering

it works like an amplifier after it attenuates the signal , without knowing anything about it , the practice is to divide HV and LV circuits so i guess its nice to have optocoupler in there somewhere , and there you go Frankenstein is your Uncle(Bob) , TEchtronics says "1000$ please" :)

Nice video!

just amazing Dave you're awesome

is the Davecad 2.0? Advanced big drawing surface with grid :)

great explained anyway my question is why it should use jfet transistor type not the other ones ?

Hi, Dave! Thanks for the video. Do you could say if the output coaxial cable is terminated? Thanks in advance

I built a probe based on this video I did a 750 meg ohm instead of 4 meg ohm I built mine to test high voltage on vintage tv sets I used triodes to build the diff amp

So with my first oscilloscope, a nice and cheap Hantek 6022BL, the protection concern comes in more of the form of the computer it’s plugged into, not necessarily the scope itself. I want to measure various parts of switchmode power supplies, so would I be looking at a differential probe, or an isolated probe? Cheers!

Isn't the DIL14 IC just a negative/symmetrical voltage converter? Probe is powered with a single 6V source. So I guess it has to have a symmetrical voltage converter for the diff-amp. Something like MAX865.

no earth mains in the outlet in Norway. Hi i was watching your other video you showed a bit about osiliscope ground clip. My house has only grounded outlet in the kitchen and in the bathroom. Do i get wrong signal if i probe my arduino without earth mains on a osciliscope? New house have mains earth over all.

Thanks so much again every time what an entertainer you are !

For us new players , using one of these as default - lets say probing around the inside of ham radio , that is plugged into AC , incase we accidentally come across AC side of things while probing around ?

so if i put an isolation transformer on the switching power supply to mesaure and then use this kind of differential probe, can i blow a channel of the oscilloscope? maybe the floating voltage rise above 700v and something goes wrong. thanks.

would one of these let you test flyback voltages on a digital scope?, i use an old hameg 40mhz analogue scope and a 1000x probe, for testing flyback on pulse induction metal detectors, but it would be nice just to use the modern scope for everything.

In series arranged capacitors should have bleeding resistors, not just for balancing purpose.

I was thinking for some time I would like to sit down and build my own differential probe is there any particular op amps that you would recommend

And they scrubbed the numbers from new board as well.

This was interesting!

Thanks!

8:10 - Those caps are mourning :)

Still sold at Farnell under different names... We have it under two other brands.

Maybe the use of 3 parallel capacitors in the voltage divider is to reduce the parasitic inductance for better high frequency performance?

Excelente Parabéns

Does this require battery, or does it actually power itself by the power source you''re testing?

Dave: Probably just some obscure company Vishay SC: that hurt mate.

I wanted to ask if you could ever do a video explaining how to read a circuit diagram and go over what the basic electronics components do? I understand this is below the scope of your blog and it's geared towards people who already know this stuff. However I can't be the only person watching who is clueless and just finds what you do entertaining. I'd like to follow along more is all. I've looked elsewhere but I think you are good at getting things across so I thought you explaining in simple non electronic terms would help. Just an idea! Love the channe.

I'm no expert, but I know from experience that when you want to measure a signal you want to receive it as unedited as possible, so to me it already seemed obvious that there would be no real isolation as it would require recreating the signal which could easily cause contamination.

I think one side is the 10 to one split ratio and the other side is 100 to one split using feedback opamps I think you forgot about the selection switch

If I just try to probe mains with a grounded oscilloscope using this probe, won't I get current from live to earth through those resistors, which would completely mess up my readings?

Why is the board in the thumbnail all blurred out?

9:36 reminded me of hail and pace with the banana.

There is a LT1818 I think as it is a wide bandwidth chip.

10:45 But what about voltage sharing, for the caps I mean? Is there not a risk of one cap having a higher than 1 kV voltage over it?

Would that be the same Sapphire that made my graphics card?

Perhaps the triple caps are an attempt to avoid the potential resonance from a simple cap.

Why does the input have almost none of the protection components that would be found in a multimeter? No MOVs, PTC, etc... Why are these components not needed for this device if it is rated to similar voltages as a multimeter? Would they lower the specs ie bandwidth? Why does it seem like this probe is held to lower safety/protection standards? Like Dave would have torn this thing a new one if he found those back to back resistors 'flappin in the breeze' if this was in a $300 multimeter. Why is this acceptable in a HV probe?

6:55 whats with the jaggedness of the traces?

I would use two channels on my scope and use the subtract function.

From 9:08 you can see how Dave is just not on his better days... there is a freaking resistor soldered to another (completely off-board) and he calls it NEAT? Where is Dave, can someone bring him back please?

The OLED display on the Keysight U1461A degrades with time. My display died after about 4 years and there is no replacement part, you have to buy a new one. Very bad support form Keysight.

Would something like this still be built with throughhole components for some reason, or is it just because it's old?

That negative lead solder joint... Eww

I see they're using a potential divider here but why is that not enough? Why the amplification?

how about cmrr measurement?

You said you wanted a Schematic. Here is a link for a High-Voltage Differential Probe. circuitcellar.com/research-design-hub/high-voltage-differential-probe/

Why are these so expensive other than being a relatively specialist item?

*Mr.Wu*

0:41 captions: How not to blow up your ass illus scope

Why does this not look like a $500 piece of equipment?

scrubbing of those numbers is how you learn karate

Why is the pcb in the thumbnail intentionally pixelated?

@Dave i think they scrub off the numbers just to get under your skin lol

Mistake at 9:41 "another 100Meg resistor"

The cheap Chinese 100MHz for 120 bucks differential probes have 1:50 or higher attenuation. I would love to see a hobbyist affordable 1:10 / 1:100 probe. Basically exactly what Dave is showing but cheaper.

IT’S OVER 9000! (Sorry, I’ll go away now.)

Why is it all through-hole and not surface mount?

Why would one use a differential probe instead of just using two normal probes on two channels without the ground clips connected and taking the difference between the channels?

why's it camouflaged?

jewel jfet? What's that?

is that a high voltage differential probe in your pocket or are you just happy to see me?

someone did some schematics over here www.diyaudio.com/forums/equipment-and-tools/248505-differential-probe-reverese-engineered.html

DaveCAD

It's a low voltage deferential probe.

LeCroy as in Teledyne LeCroy?

so that's how you test mains

Take it apaaaart! :D I keep laughing at that :)

2:52 "you can come a-..." what? What is he saying?

So u basically pay 700 $ for two 4 Meg resistors?

Never understood why you need a junk like this. If you have a dual input oscilloscope and subtract the inputs, it should work for low frequency signals. These gadgets never work for giga Hertz anyway. If need to measure independent signals from ground, there are very good scopes that have isolated inputs from ground.

first

max 1000v.......... That's still LV not HV.

I wouldn't call this unit a "High Voltage" Probe. It is only suitable for mains-voltages which is called "low voltage" in terms of electrical energy grids. If you're talking about HV, one would exspect somthing more in the range of 10kV upwards. Lastly, the unit itself doen't say High-Voltage anywhere. Also as you should know the little lightning-symbol doent's mean high voltage, it just means "dangerous voltage".

wow this is cheap build quality... 😕

01/29/22 Micsig DP10013 High Voltage Differential Probe 1300V 100MHz 3.5ns Rise Time 50X/500X Attenuation, Tektronix P5200A P5205A P5210A $200 🧐great probe info ☕🍰

The resistor is not for offset, but to maximize the common mode rejection ratio. If one of the 4meg is actually 4meg+1% and the other has 4meg-1% then the CMRR is only 34dB. With the resistor you can tune the CMRR for DC to much higher values.