Budget 2 isolated channel bench oscilloscope?

[drummerdimitri]

I've been having issues with my Rigol DS1054Z when measuring audio signals and rectified mains voltage on many occasion so I'm not using it any more in fear of damaging something.

It occurred to me that I would much rather lose 2 of those 4 channels and get the remaining 2 isolated so I no longer have to worry about shorting equipment and ground loops.

Would you recommend any bench scopes under 600$ with two isolated channels? If I find an appropriate model, I will put up for sale my Rigol.

[thanasisk]

Perhaps one of the micsig oscilloscopes or using an active differential probe as an alternative?

[nctnico]

For mains: get a differential probe. For audio purposes it is not difficult to make a differential amplifier from an instrumentation amplifier. I also think that $600 might not be enough to get an oscilloscope with isolated channels (many of the cheap handhelds don't have isolated channels!). Besides that most handheld scopes are crappy; they are extremely limited compared to a regular bench top oscilloscope. The ones from MicSig are rare exceptions but these don't have isolated channels.

[drummerdimitri]

For mains: get a differential probe. For audio purposes it is not difficult to make a differential amplifier from an instrumentation amplifier. I also think that $600 might not be enough to get an oscilloscope with isolated channels (many of the cheap handhelds don't have isolated channels!). Besides that most handheld scopes are crappy; they are extremely limited compared to a regular bench top oscilloscope. The ones from MicSig are rare exceptions but these don't have isolated channels.

I have heard of differential probes, however I believe they are extremely expensive if I'm correct. Will these isolate the scope from the mains?

Not sure about the differential amplifier you talked about. Maybe some more info would be useful as I am not familiar with the idea.

[tautech]

200 MHz 2ch SDS1202X-E coupled with ISFE for 2 fully isolated channels costs $ 379 + $ 135
https://siglentna.com/digital-oscilloscopes/sds1000x-e-series-super-phosphor-oscilloscopes/
https://siglentna.com/product/isfe-isolated-front-end/

User manual:
https://int.siglent.com/u_file/document/ISFE_User_Manual.pdf

Its drawbacks are 200:1 attenuation and 1 MHz max frequency.
ISFE couples directly onto Siglent DSO inputs while other brands use different input spacings so short BNC cables are also required for use with other scopes.

[nctnico]

For mains: get a differential probe. For audio purposes it is not difficult to make a differential amplifier from an instrumentation amplifier. I also think that $600 might not be enough to get an oscilloscope with isolated channels (many of the cheap handhelds don't have isolated channels!). Besides that most handheld scopes are crappy; they are extremely limited compared to a regular bench top oscilloscope. The ones from MicSig are rare exceptions but these don't have isolated channels.

I have heard of differential probes, however I believe they are extremely expensive if I'm correct. Will these isolate the scope from the mains?

Around $180 from MicSig for example. These will isolate the scope from mains (the ones from MicSig have a CAT rating).

Not sure about the differential amplifier you talked about. Maybe some more info would be useful as I am not familiar with the idea.

Just look at analog devices, TI, etc for an instrumentation amplifier chip. This will take a differential signal and create a single ended output. The bonus is that you can choose to amplify the signal too.

[drummerdimitri]

200 MHz 2ch SDS1202X-E coupled with ISFE for 2 fully isolated channels costs $ 379 + $ 135
https://siglentna.com/digital-oscilloscopes/sds1000x-e-series-super-phosphor-oscilloscopes/
https://siglentna.com/product/isfe-isolated-front-end/

Its drawbacks are 200:1 attenuation and 1 MHz max frequency.
ISFE couples directly onto Siglent DSO inputs while other brands use different input spacings so short BNC cables are also required for use with other scopes.

Can't I used that ISFE isolated front end on my Rigol?

Not an issue regarding the 1 Mhz frequency as most of my work involves audio, PWM signals and mains voltages etc.

If that's the best option I will seriously consider it.

[nctnico]

200 MHz 2ch SDS1202X-E coupled with ISFE for 2 fully isolated channels costs $ 379 + $ 135
https://siglentna.com/digital-oscilloscopes/sds1000x-e-series-super-phosphor-oscilloscopes/
https://siglentna.com/product/isfe-isolated-front-end/

Its drawbacks are 200:1 attenuation and 1 MHz max frequency.
ISFE couples directly onto Siglent DSO inputs while other brands use different input spacings so short BNC cables are also required for use with other scopes.

Can't I used that ISFE isolated front end on my Rigol?

Yes but the 200x attenuation ratio makes it utterly useless. Just get the MicSig differential probe for mains use. Best bang for the buck.

[tautech]

200 MHz 2ch SDS1202X-E coupled with ISFE for 2 fully isolated channels costs $ 379 + $ 135
https://siglentna.com/digital-oscilloscopes/sds1000x-e-series-super-phosphor-oscilloscopes/
https://siglentna.com/product/isfe-isolated-front-end/

Its drawbacks are 200:1 attenuation and 1 MHz max frequency.
ISFE couples directly onto Siglent DSO inputs while other brands use different input spacings so short BNC cables are also required for use with other scopes.

Can't I used that ISFE isolated front end on my Rigol?

Not an issue regarding the 1 Mhz frequency as most of my work involves audio, PWM signals and mains voltages etc.

If that's the best option I will seriously consider it.

You can as it only requires USB power however unless you have a 200:1 channel input attenuation setting amplitude values will need to be calculated in your head.

There’s a thread about ISFE here on EEVblog you can hunt out for further info.

[maginnovision]

Just get a diff probe and call it a day. Use it for mains and directly probe audio. The probe is made for any scope and the isfe isnt, even though you can make it work. Listen to nctnico and save yourself trouble.

[james_s]

I will second this. I picked up a Tektronix P5205  differential probe for $120 after reading about them on here, it's been so useful I wish I'd bought one sooner. I was only vaguely aware they existed before that and now I use it all the time.

[Fungus]

I've been having issues with my Rigol DS1054Z when measuring audio signals and rectified mains voltage on many occasion

...

If I find an appropriate model, I will put up for sale my Rigol.

For sale: Rigol DS1054Z, one careful owner.

[maginnovision]

Haha, never abused, barely used. Like new.

I blew up a probe a while back though not thinking. Technically the probe still worked but the short ground attachment was MIA after a loud noise, assumed vaporized. So I can't laugh too much.

[BravoV]

...  so I no longer have to worry about shorting equipment and ground loops.

.... I will put up for sale my Rigol.

Just get HV diff probe as many already suggested above, it will relief you big times at your above worries, and also as time goes by, when you decided you want to replace your current Rigol, you still can use it for your upcoming new scope in the future.

Just an example on how stress free to probe directly anything at AC mains voltage level, as below example the scope was probing straight at the AC mains that powered the scope it self.

[drummerdimitri]

Sounds good. Will be getting a differential probe then but as there are so many on the market, what specifications should I be looking for?

[maginnovision]

Just make sure it's capable of the voltages you'll be using it at. I prefer lower ratios. The HVP 70(NLA I think) has 1/10 and 1/100 ratios and +-700V range which works well for me. The micsig probe(DP10013) is pretty popular here. You can also just search on ebay and find one that fits your needs.

http://www.micsig.com/html/41.html

[drummerdimitri]

Will lower ratios be more accurate in terms of absolute voltage measurements? Surely the relative waveforms will be of the same shape.

[maginnovision]

Higher division ratios mean more noise from the probe itself but different probes have different levels there too. Yes the waveforms will, but if your division is too high and/or the measurement too low you're relying even more on the scope having a good low noise floor. The 1054Z is not a good low noise scope. For mains it's not a problem but who knows when you'll need to probe other lower voltage mains referenced signals. Just for mains you're probably safe with most probe that are ok with the voltage.

[Electro Detective]

First up, this time I checked that the OP is using a Rigol and not a Siglent,
as per a previous king sized post blunder on my part 


That said, would running the scope in ch 1 and ch 2 differential mode, with its limitations,

plus two external differential probes on ch 3 and ch 4

yield a poor mans three channel isolated DSO ?

Can't see why it won't work, and  ch 1 and ch 2 differential mode could double as an isolated trigger

 

[drummerdimitri]

I did some digging and found the Pintek DP-25 to be a more suitable option for my uses as the minimum of 50x attenuation of the Micsig will not be so great for audio measurements but the 200x for mains will be the same on the Pintek DP-25 and the Micsig.

I like the x20 of the Pintek DP-25 better for low level signals as it will give me less noise and since I don't realistically need over 1 MHz of bandwidth I think the Pintek is the better option unless someone can prove otherwise. 

[thanasisk]

You can have a look also at the differential probes by Testec.

Pay attention to the maximum voltage specs depending on the range. Some diff probes offering also 1:1  have very low max voltages for those modes.

[drummerdimitri]

You can have a look also at the differential probes by Testec.

Pay attention to the maximum voltage specs depending on the range. Some diff probes offering also 1:1  have very low max voltages for those modes.

I just did and it is the equivalent of the Testec TT-SI-7002 which looks exactly the same so my guess is they are just re-branded probes and is a bit more expensive so would rather get the Pintek in this case as it is available on Aliexpress for 225$ shipped!

[nctnico]

I did some digging and found the Pintek DP-25 to be a more suitable option for my uses as the minimum of 50x attenuation of the Micsig will not be so great for audio measurements but the 200x for mains will be the same on the Pintek DP-25 and the Micsig.

I like the x20 of the Pintek DP-25 better for low level signals as it will give me less noise and since I don't realistically need over 1 MHz of bandwidth I think the Pintek is the better option unless someone can prove otherwise. 

You shouldn't use differential probes like the DP-25 for audio anyway. Just go the differential amplifier route for that.

[maginnovision]

Yea standard diff probes add enough noise that it's not a great idea for audio. I'd prefer direct probing or proper LNA which gives you the bigger signal without the added noise. I've used https://www.alphalabinc.com/product/lna10/ and it's typically been pretty good the seller is also responsive.

You could also make your own if you'd like to go that route.

[tautech]

I did some digging and found the Pintek DP-25 to be a more suitable option for my uses as the minimum of 50x attenuation of the Micsig will not be so great for audio measurements but the 200x for mains will be the same on the Pintek DP-25 and the Micsig.

I like the x20 of the Pintek DP-25 better for low level signals as it will give me less noise and since I don't realistically need over 1 MHz of bandwidth I think the Pintek is the better option unless someone can prove otherwise. 

Yep, you're onto it.
DP-25 is a well priced option that I also stock.