VOLTCRAFT DOV series

[Aldo22]

Basically, you can only measure a time delay between the trigger input and the trigger output.

I don't quite understand. Can you explain?

[tautech]

Basically, you can only measure a time delay between the trigger input and the trigger output.

100%

A scope is a time domain instrument where channel/measurement skew/misalignment matters.

Signal propagation delays are real and addressed in many ways and the primary reason why we have 2, 4, 6 and 8ch scopes.

Taking this to the extreme are instruments like SDS5000L and SDS6000L, 4 or 8ch headless DSO's all time synced together .....up to 64 units and 100's of channels.....all remotely controlled as 1 unit if needed.

[Aldo22]

@tautech:
One of the reasons I decided against the 4-channel model was a post you wrote. 

If you already own a 2 ch scope then there are ways to use another 2 ch unit to get the info you need and still get close timing relationships with Trig In/Out etc.

I can count on one hand the times I've needed 4 channels and I wouldn't have needed 4 if I used 2 scopes.

[tautech]

@tautech:
One of the reasons I decided against the 4-channel model was a post you wrote. 

If you already own a 2 ch scope then there are ways to use another 2 ch unit to get the info you need and still get close timing relationships with Trig In/Out etc.

I can count on one hand the times I've needed 4 channels and I wouldn't have needed 4 if I used 2 scopes.

Close depending on what you are doing might be not good enough.

As I mentioned a few posts back, scopes are time domain tools and excel at that but 2 linked DSO's are never as accurate as one.
I can count on 1 hand how many 2ch DSO's we've supplied in the last 2 or 3 years whereas the vast majority have been 4ch models, from 70 MHz to 1 GHz.
The only 2ch a SDS802X HD sold this year went out the door last week.

Years back before teaming up with Siglent I played with magnetics optimising Mosfet ON time without saturating the magnetic to maximise its output (back EMF) using voltage and current probes were channel skew due to the different propagation delays of each probe type affected the measurement result.
It's real and I've witnessed it and yes 2 channels are often enough until they aren't.

[Aldo22]

Close depending on what you are doing might be not good enough.

As I mentioned a few posts back, scopes are time domain tools and excel at that but 2 linked DSO's are never as accurate as one.

Sure, but we’re talking about two of the cheapest entry-level benchtop scopes out there.
I paid CHF 126 for the DSO2000 and 149 for the DOV702.
The Voltcraft triggers the Hantek.
Everything’s fine on my end.

If I had higher demands, I’d get a device that meets them.

[Aldo22]

The “Hi-Res” mode is effectively useless.
It has no effect on the measurements, and I ultimately confirmed this with the Bodnar pulser.

I can definitely measure an effect.
See VPP/VRMS Avg.
With HR, the noise is reduced.
Perhaps not across all ranges and settings.

[2N3055]

I believe it is called sunk cost fallacy.

Those two combined sum up to 400 €. And if we add few Finrsi small toys you mentioned you own, that adds up to price of SDS814xHD.
Which would mean that instead of bunch of questionable devices that all have many compromises and are, well, almost toys, you would have one professional level device.

Same thing as a friend of mine has dozens upon dozens of 10€ bit sets from Lidl and was amused how rich I am to buy a premium quality set of mini 4mm bits from Wiha that was some 80€. While he literally has 100-150€ worth of duplicate sets that do not have even close different types, and when you look the tips under magnification, Wera ones are picture perfect and his ones are at best hit and miss...

I could understand getting one cheap set because you don't have that kind of money and you are frugal and then you get what you get.
Getting larger number of inferior products means you never get anything of good quality despite spending lots of money.

That is my thinking.
That is why I save up a little bit and get the right stuff.
There is an old saying "I am not rich enough to buy cheap things".. Of course that is gross simplification if taken literally, but as a principle makes sense in a long run.

And I am not a snob by any measure. I do not think that any "premium" brand gives value by virtue of the name. I do own some Einhell tools, and quite a lot Parkside tools, where quality is good enough for what I do. But some precision tools, measurement instruments, etc. need some quality level to be considered to be useful. If a scope has a ripple on the trace with nothing connected, it is broken. As in in need for repair, not fit for use. I don't care how cheap it is.

Of course that is my philosophy that I live by.
Other people have their own. I don't have to agree with it  or understand it.

[evava]

aldo22 lives in Switzerland, 400 CHF is probably his monthly health insurance payment and about 5 percent of the monthly median wage, so..

[Aldo22]

Those two combined sum up to 400 €. And if we add few Finrsi small toys you mentioned you own, that adds up to price of SDS814xHD.
Which would mean that instead of bunch of questionable devices that all have many compromises and are, well, almost toys, you would have one professional level device.

Are you talking about my two cheap oscilloscopes?
How did you come up with €400?
CHF 126 + 149 = CHF 275 = €300
I've had the Hantek for 2.5 years now and have really enjoyed playing around with it.
Now I’m having fun with the Voltcraft (and still the Hantek).

I don’t need a professional-grade scope because I’m not a pro.

I’m also very happy with the two Fnirsis, the DPS-150 and the SG-003A, and would buy them again.

I were a pro, I’d buy different qualities, but “Toys” are fine for me.

You don’t have to understand that... 

[2N3055]

Those two combined sum up to 400 €. And if we add few Finrsi small toys you mentioned you own, that adds up to price of SDS814xHD.
Which would mean that instead of bunch of questionable devices that all have many compromises and are, well, almost toys, you would have one professional level device.

Are you talking about my two cheap oscilloscopes?
How did you come up with €400?
CHF 126 + 149 = CHF 275 = €300
I've had the Hantek for 2.5 years now and have really enjoyed playing around with it.
Now I’m having fun with the Voltcraft (and still the Hantek).

I don’t need a professional-grade scope because I’m not a pro.

I’m also very happy with the two Fnirsis, the DPS-150 and the SG-003A, and would buy them again.

I were a pro, I’d buy different qualities, but “Toys” are fine for me.

You don’t have to understand that... 

Of course, you do you. It is your life.

I explained that I, myself, would put together all the money you gave for all "toy scopes" (don't get me wrong, these are not useless, they have some usability but very limited) including 2 Finrsi ones and got myself SDS800xHD. That would give me one professional for the same cost. To me (personally) that makes more sense. And those 4 together combined do cost the same.

You probably think differently and therefore you like more of the less, than less of the more... To each it's own...

Best.

[Aldo22]

Of course, you do you. It is your life.

If you feel it's important to share these thoughts, please start a separate thread for them.
Don't get me wrong—I've really appreciated your expertise on several occasions—but I don't want to continue this discussion here.

This thread is about the Voltcraft DOV series (or the Owon ADS800A).

- What’s good
- What sucks
- Tips and tricks
- Improvements and hacks
- Resources, etc.

Thanks!

Here’s another resource that should actually work on the VC DOV as well: https://www.eevblog.com/forum/testgear/owon-ads-web-app/

[Martin72]

Hi,

The replacement unit arrived today—and, “of course,” has the same problem.
Counting Aldo's Scope, Lutz's, and mine (that makes two), there are now four units affected.
This is no longer a coincidence, but a systemic issue.
And when you measure the calibration output using the vertical setting—where the ripples appear—it looks even worse.
Good to know:
If you switch the coupling to GND, the problem goes away, so at least I have an idea of where to look.
It won't be easy.

[Aldo22]

The replacement unit arrived today—and, “of course,” has the same problem.

This is no longer a coincidence, but a systemic issue.

Yeah, it is kind of weird that it went into production like that.
Do you think it could be fixed with a firmware update, or is it a hardware issue?

Did Conrad say anything when you exchanged it?

I actually like a lot of things about this scope, but this bug is pretty bad.
I’ve been thinking about returning it, too.

[Martin72]

Hi,

I don't think it's a firmware bug.
Conrad didn't say anything about it and just sent a new one without comment.
I'm thinking about whether I should contact Owon about this.
I opened up the scope earlier—no problems, since there are only a few screws and no seals.
Pictures to follow.
The ADC is a Ti ADC12L500; there are two of them.

[KungFuJosh]

There is an old saying "I am not rich enough to buy cheap things"..

I also like the saying "buy cheap, buy twice." ...Or in your friend's case, dozens of times.

[shabaz]

I think this is relevant to this thread. For a beginner they are not even that cheap to be worth it. Even without saving up a bit more, one could have just bought a used low-end HP 'scope (I'm only using HP as an example here because there are many of them on ebay usually; replace with any other well known brand if you want) for that price or lower; or perhaps got a free 'scope donated from someone.

I don't mind buying low-cost lesser-brand  or no-brand stuff, but some equipment (digital 'scopes being the epitome of this) are inherently complex enough it's silly not to expect there to be perhaps quite significant limitations or idiosyncracies if implemented on the cheap particularly by firms with no heritage/specialization.

I gave away a couple of known-brand 'scopes for free, and I'm not atypical; it's very feasible for people to pick up known brand ones for little or no cost. And sometimes one has to charge a nominal fee, people don't trust free or may feel uncomfortable accepting things for free.

Even a brand new PicoScope 2000 series costs ballpark 150 euro probably (I have not checked prices recently). Not enough bandwidth, or missing some features? Here are some solutions; firstly, with respect, for hobbyists sometimes it's possible to pivot your experimentation/learning curve to suit your budget/equipment, until you have studied or worked a few years, to either learn any possible alternatives or workarounds, or until your salary has risen enough to to buy better equipment, or make some friends, there are hackerspaces, amateur radio groups and so on, it's not that hard to find a 'scope to use temporarily if really needed. Just needs a little thinking outside the box, and perhaps some socializing to go meet these groups or make friends with fellow engineering enthusiasts, some may even have the test equipment you wish to use.
Plus. A hobbyist can afford to get creative with solutions. Recently I soldered up an analog circuit, I didn't have all the equipment to test it, but I built up a second kit of parts and sent that to a friend who did own the test equipment, and he kindly assembled and tested it, and I learned a lot, and could compare measurements with my more limited equipment, and I didn't let my lack of equipment stop me. And I've sometimes helped out by trying to replicate circuits if I have the test equipment but others do not; I'm not special, plenty of people help in this way on forums, whatsapp tech groups, makerspaces etc., helping fellow enthusiasts, who may have limited equipment or need assistance.

[Martin72]

Hi,

The pictures...
The heat sink is actually just a relatively thin plate, which explains why the offset changes immediately when the fan starts up.
The fan itself is a three-pin model.
The front end looks “normal” at first glance, but the problem with the ripple at 200 mV/div must be somewhere there.
A relay is activated at 200 mV/div; I need to look for it somewhere, but I’ll have to think that over.

[Aldo22]

I think this is relevant to this thread.

No, it isn't.

Could you please discuss your shopping philosophies and unasked-for words of wisdom in a separate thread? 

Thank you!

[Aldo22]

Hi,

The pictures...
The heat sink is actually just a relatively thin plate, which explains why the offset changes immediately when the fan starts up.
The fan itself is a three-pin model.
The front end looks “normal” at first glance, but the problem with the ripple at 200 mV/div must be somewhere there.
A relay is activated at 200 mV/div; I need to look for it somewhere, but I’ll have to think that over.

Thanks for the photos. 

That's also the final proof that it's an Owon ADS800A.

[tautech]

Hi,

The pictures...
The heat sink is actually just a relatively thin plate, which explains why the offset changes immediately when the fan starts up.
The fan itself is a three-pin model.
The front end looks “normal” at first glance, but the problem with the ripple at 200 mV/div must be somewhere there.
A relay is activated at 200 mV/div; I need to look for it somewhere, but I’ll have to think that over.

   

What do you see immediately that's vastly different to most other DSO front ends ?
They must be short of shielding metal where these come from........

Good luck getting rid of that waveform ripple. 

[Martin72]

I removed the shielding plates...

You can remove them without soldering; they were secured on two sides with a drop of glue.

[tatel]

Could you please go back to reply #1?

I would go for the similar siglent DSD804X HD to get 2 GSa/s and 500,000 waveforms/s for just a little bit more?

https://www.siglenteu.com/digital-oscilloscopes/sds800x-hd-digital-storage-oscilloscope/

Also:

I would feel much more comfortable putting my money into the Siglent. I would say, it's a much more tested device, from a much more reputable brand. For me, it would really be that simple. But, of course, those that don't explore, don't find any treasures.

I guess this thing is not a treasure after all. Unfortunately explorations are not always successful. But, any lessons are earned best by wasting one's own money.  So it's not a total waste in some kind of way. Moreover, for many people here, this is a cheap confirmation that our bias towards better known hardware is sound. So, even less of a waste for the community. Thank you very much for that.

I hope you can still  return it and get your money back, or, alternatively, invert time and more money to hopefully fix it. I think returning it would be best to make the vendor realize it's not a very good product. But fixing it could be a very enjoyable adventure, so why not?

Good luck

[Filippo52]

Martin
I see two ADCs that you label Ti ADC12L500. I tried looking for them, and the lower-performance one with 0.5 G on two channels and 1 G on one channel costs as much as the entire oscilloscope. I understand that the manufacturer buys them in bulk, but perhaps I misidentified the type? Would the two ADCs, separately, cost twice as much as the oscilloscope?

Filippo

[Aldo22]

The front end looks “normal” at first glance, but the problem with the ripple at 200 mV/div must be somewhere there.
A relay is activated at 200 mV/div; I need to look for it somewhere, but I’ll have to think that over.

@Martin72: While trying to track down the ripple phenomenon, I discovered something strange that might help you with the diagnosis.
The look of the ripple seems to be related to the frequency of the input signal!
And even crazier: it affects both channels.
Take a look at the screenshots:
The only difference between the two images is the frequency on the signal generator (100 Hz, 1.5 kHz).
Nothing is connected to the second channel.

EDIT: Or is that just the trigger?

[Aldo22]

Could you please go back to reply #1?

I would go for the similar siglent DSD804X HD to get 2 GSa/s and 500,000 waveforms/s for just a little bit more?

https://www.siglenteu.com/digital-oscilloscopes/sds800x-hd-digital-storage-oscilloscope/

I actually didn't want to respond to any more “We told you so” posts, but since you were the first to reply, I'll make an exception. 
It doesn't just cost a little more here—you get three DOV702s plus CHF 33 for pizzas in exchange for a DSD804X HD (149.- vs 483.30).

Even I knew the Siglent was better, but that's not the point.
If everything just works and everyone has already figured out everything about the device, where’s the fun in that? 
I do admit, though, that I wouldn’t have expected something like the ripple problem.
I had expected bugs in the secondary features, but not in something so fundamental.
I could still return it—we’ll see.

Good luck

Thank you!