VOLTCRAFT DOV series

[evava]

I have one more question for Aldo22: (I appreciate that you bought the device among the first, back when its full range of features and flaws wasn't yet clear.)
If you were to buy the device today—now that you are thoroughly familiar with it—would you buy the two-channel version again, or would you rather pay extra and get the four-channel version?

[Aldo22]

If you were to buy the device today—now that you are thoroughly familiar with it—would you buy the two-channel version again, or would you rather pay extra and get the four-channel version?

I don't need 4 channels, so I'd buy the 2-channel model again.
To me, the extra cost doesn't make sense—in 1-channel mode, the devices are exactly the same.
If you have a use for 4 channels, then buy the 4-channel model.
You'll have to decide that for yourself.

[SL75]

I have one more question for Aldo22: (I appreciate that you bought the device among the first, back when its full range of features and flaws wasn't yet clear.)
If you were to buy the device today—now that you are thoroughly familiar with it—would you buy the two-channel version again, or would you rather pay extra and get the four-channel version?

The really big advantage of the 4-channel device is the second built-in 12-bit ADC, which is probably what determines most of the extra cost. This way, you get the full sample rate (1.25 GSa/s) in two-channel mode, which is only possible in single-channel mode with the two-channel device. 
Optionally, you can study 4 signals if you ever need to… 
Personally, I would only buy 4-channel devices with at least two ADCs, especially when the extra cost, as in this case, is minimal.

[Aldo22]

...especially when the extra cost, as in this case, is minimal.

Here (CH), the extra cost isn't minimal—it's 47%. That's a lot for something I'll probably never need (4 channels).
The two ADCs could be an advantage.
However, the reconstruction is quite good, so even with the 2-channel model, a square wave at nominal bandwidth still looks very good even when using two channels (Screenshot).

It’s always like that when making a purchase: For a little more, you get a little more.
It’s always tempting, and I’m not immune to that either.
But you can always ask yourself: Do I really need this?
For me, the 2-channel model is the most attractive deal.

Like I said: Everyone has to decide that for themselves.

[TomC]

...especially when the extra cost, as in this case, is minimal.

Here (CH), the extra cost isn't minimal—it's 47%. That's a lot for something I'll probably never need (4 channels).
The two ADCs could be an advantage.
However, the reconstruction is quite good, so even with the 2-channel model, a square wave at nominal bandwidth still looks very good even when using two channels (Screenshot).

It’s always like that when making a purchase: For a little more, you get a little more.
It’s always tempting, and I’m not immune to that either.
But you can always ask yourself: Do I really need this?
For me, the 2-channel model is the most attractive deal.

Like I said: Everyone has to decide that for themselves.

All the other scopes I own are 2 1/2 channels, meaning they have an external trigger input. The ADS/DOV series doesn't offer an external trigger input. In my case, that's the reason I chose the 4-channel model. I can't remember a time I actually needed 4 channels.

[Aldo22]

All the other scopes I own are 2 1/2 channels, meaning they have an external trigger input. The ADS/DOV series doesn't offer an external trigger input. In my case, that's the reason I chose the 4-channel model. I can't remember a time I actually needed 4 channels.

That's true, but it has a trigger output.
If you combine it with an oscilloscope that has an external trigger option, you'll also have 4 separate channels with a single trigger channel.
There's a slight constant delay, but you can correct for it.
Of course, this isn't quite the same as a 4-channel oscilloscope, but it should be enough if you ever need it.

[evava]

Stocks are runing low —what happens next?
Will no more units be produced, or will the newer (revised) ones come at the new (original) price?
Does anyone have any idea?

[TomC]

All the other scopes I own are 2 1/2 channels, meaning they have an external trigger input. The ADS/DOV series doesn't offer an external trigger input. In my case, that's the reason I chose the 4-channel model. I can't remember a time I actually needed 4 channels.

That's true, but it has a trigger output.
If you combine it with an oscilloscope that has an external trigger option, you'll also have 4 separate channels with a single trigger channel.
There's a slight constant delay, but you can correct for it.
Of course, this isn't quite the same as a 4-channel oscilloscope, but it should be enough if you ever need it.

That's a clever workaround, and may be useful with other instruments, like an SA or VNA with an external trigger input. Too bad my SA lacks that feature. In reality, I don't often have a need for an external trigger, most of the time the chosen trigger is something I also want to see. However, for decades, back all the way to my Tektronix analog scopes, I've been used to having it available, so I thought with 4 channels one of them could take the place of the external trigger I've been accustomed to.

[Filippo52]

I'm very curious to see what will happen; I still haven't figured out what marketing strategy the manufacturer/distributor has adopted, and I don't understand how it will continue.
I hope it's not just a rush to eliminate a stock of defective products, because even if Volfcraft doesn't have a great name to uphold, selling off defective products that can't be repaired with new firmware releases, much less with recalls could easily tarnish its reputation.

Meanwhile, in addition to the various defects, I also have doubts about the possible differences with the higher-performance models, which can cost up to €1,000, making them almost more expensive than much more renowned competitors.
- Is the 250 MHz only available on the top model, or are there "hacks" like many others?
- Is it true that the components in the top models are of better quality?
- No one knows the "noise" characteristics or the ENOB of these oscilloscopes. Some claim, but I haven't found any confirmation, that the DOV 704's ENOB is only 6.5 bits, making the advertised 12 bits virtually useless.

In any case, I'll continue to follow this thread with interest, which I believe has become a point of reference on the internet for this oscilloscope.

Filippo

[Martin72]

@evava:
You just have to accept that the special offers for the DOV702/704 are one-time deals that disappear once the stock is sold out.
Whether Conrad is selling them off at a discount because there were too many returns or because they simply didn’t sell enough of them at the regular price remains a matter of speculation.
Both could be true, because as they are, people usually return them due to the obvious failures.
And the regular price was so high that there are better alternatives.
So they decided to sell them off at a huge discount.
I don't think they'll restock it.
To do that, they'd have to order a certain amount from Owon again, and then they'd be back in the same situation.
Once you reach a certain purchase quantity, you can purchase custom logos, custom splash screens, etc.
Take a look at Alibaba—you’ll find relevant offers there.
Voltcraft has always been Conrad’s private label, just like RS Pro at RS Electronic.
Both are merely retailers; they don’t manufacture anything.
So I wouldn't worry about the “future” of a secondhand item.
Let's just enjoy the opportunity that presented itself to get a 12-bit scope with a "few" quirks at an unbeatable price.
I'm going to equip my second DOV704 with everything I/we figured out to turn it into a decent scope—and then I'll either sell it for the same price or put it somewhere where it won't gather dust.
Unfortunately, my nieces and nephews aren't into technology; otherwise, I would have given it to one of them...

[Martin72]

Meanwhile, in addition to the various defects, I also have doubts about the possible differences with the higher-performance models, which can cost up to €1,000, making them almost more expensive than much more renowned competitors.
- Is the 250 MHz only available on the top model, or are there "hacks" like many others?
- Is it true that the components in the top models are of better quality?
- No one knows the "noise" characteristics or the ENOB of these oscilloscopes. Some claim, but I haven't found any confirmation, that the DOV 704's ENOB is only 6.5 bits, making the advertised 12 bits virtually useless.

Is the 250 MHz only available on the top model, or are there "hacks" like many others?

The DOV704 (and probably the 702 as well) has a bandwidth of just under 180 MHz.
That’s quite a lot for a model that’s actually specified as 70 MHz, and it didn’t go any higher than when Olex released his ADS824 hack.
Which makes sense, since the DOV700 series only goes up to the 100 MHz model.
What changes as a result of the hack is the bandwidth of the frequency counter, and in my opinion, that would be the only reason to use the hack.
So I wouldn’t worry about 250 MHz of bandwidth.

Is it true that the components in the top models are of better quality?

What are you referring to?

No one knows the "noise" characteristics or the ENOB of these oscilloscopes. Some claim, but I haven't found any confirmation, that the DOV 704's ENOB is only 6.5 bits, making the advertised 12 bits virtually useless.

At least here in this thread, there's never been any mention of ENOBs, let alone “only” 6.5 ENOBs.
As for “uselessness,” the ENOB naturally decreases as the bandwidth increases.
For example, 6.5 bits is a perfectly normal value for a 12-bit scope if it has a bandwidth of several GHz.
You can probably imagine how many of those 8 bits remain in that case.
A full 12 bits isn’t achieved; if the DOV exceeds 8-bit ENOB within the limits of its capabilities, that’s OK.
The DOV700's front end isn't exactly super low-noise, and the design in general isn't all that impressive, but I'm pretty sure there's still some benefit left from having a true 12-bit ADC.

[Filippo52]

Martin, thanks for the timely and detailed response.
So if I understand correctly:
- There's no need to worry about the bandwidth, which reaches 180 MHz on its own without any modifications.
- Any firmware for the ADS824 model only increases the frequency counter bandwidth, and if it's not needed, you can leave it as is.
- Regarding quality, there's some noise, brought on by the AI, which says that higher-end models, despite sharing the same design, use higher-quality components in the front end, meaning they have lower noise.
- The same "rumors" speak of an ENOB of only 6.5 bits; 8 bits, as you say, if that were true, would be a very good result for this price range, and that's the value declared by Rigol for the MHO954.

Thanks again

[Aldo22]

That's a clever workaround, and may be useful with other instruments, like an SA or VNA with an external trigger input. Too bad my SA lacks that feature. In reality, I don't often have a need for an external trigger, most of the time the chosen trigger is something I also want to see. However, for decades, back all the way to my Tektronix analog scopes, I've been used to having it available, so I thought with 4 channels one of them could take the place of the external trigger I've been accustomed to.

I made a short video to show that this works pretty well for a “poor man's” solution.
Here, the Hantek is triggered externally.
The DOV is in control:

https://streamable.com/0vyqpz

[evava]

I still couldn't decide which one to buy, so I finally told myself I'd get the one where the remaining stock dropped to 15 first.
So, the four-channel one!

Here, the price is about 15% higher (after converting the euro exchange rate) than in Germany, but we're used to it; a lot of things are more expensive here in the former Eastern Bloc.
Fortunately, I managed to negotiate at least a 7% discount with Conrad.

I'm really looking forward to my new toy.

[goaty]

 You could have let us know, then sending it to CZ is pretty cheap (17€).
Still some left.

Ahoi !

[Arek]

success 

[Bernd9735]

Hallo together,
this is my first post on this forum. I like to thank all the peobles her who put a lot of effort and knowledge in the DOV700. I use privat an oszilloskop about 4-5 times per year. My old Oszilloscope (VDS1022i) has lost accuraty and calibration changes within hours so I need replacement. My budget was about €250 so the DOV is exactly what i need.

The rippel remove is spread ofer a lot of postings so I compiled a document that allows new users to do the modifikation without reading all the postings. Just have a look on it and tell me if all is correct and usefull.

[goaty]

There are two methods. One is replacing with zero ohms, removing the buffer, the other is the "SL75" method.
Not absolutely sure which is better.
But then there´s more to do.
- Silent fan
- Dampen 7.6kHz ripple with big capacitor at the 2.5V reference
- Ripple at the 1kHz calibrator output
- probably more...
Owon should have sold this as a kit, not an oscilloscope ;-)

The TO aldo has put together links in the very first post already.

[Martin72]

I prefer the “SL75” version; it has no problem handling the significantly increased capacitance required for the 2.5V to sufficiently attenuate the 7.6 kHz interference.

[Arek]

The “upgrade” also works with the two-channel version.
But yes, the bandwidth remains the same.

I wanted to make a “backup” first.
Here's how to do it with a FAT32 flash drive (4GB file size limit):

Code: [Select]

dd if=/dev/block/mmcblk0 | gzip > /storage/5496-CF0C/dov_backup_img.gz
Thank you Olex! 

Do I need to run the oscilloscope in some sort of safe mode to safely use this command, or can I just run it like that? I've read online that making a backup on a live system can cause some errors.

[evava]

There is only this:

Hi,

How did you solve it?
Couldn't you, for instance, revert to the original version 14, perform the model change, and only then move to version 1.8?
Do you have axis labels now, for example?

I mean: if someone upgraded straight to the latest version without performing the model change first, are they in the same mess you are—stuck and not knowing how to solve that?

[SL75]

I did it like this. From the delivered version V1.0.1.0.13 (my device must have been way in the back of the warehouse...) I went straight to the version V1.0.1.8.2 that's distributed here. I haven't done any model change so far.
Works perfectly fine so far (not counting the still built-in hardware design flaws).

[goaty]

Hi,

How did you solve it?
Couldn't you, for instance, revert to the original version 14, perform the model change, and only then move to version 1.8?
Do you have axis labels now, for example?

I mean: if someone upgraded straight to the latest version without performing the model change first, are they in the same mess you are—stuck and not knowing how to solve that?

I did not do model change so far, as it´s a bit complicated for me (needs ADB, console, python, etc) and I do not need more than 70MHz.
So I reverted to the '17' version, which works fine. Cursors work there. I asked OWON, but they do not reply.

I´m still trying out the power supply issue with the grounding. So far no luck. I tried a USB-C brick, but the noise is much worse than on the delivered unit.

[Aldo22]

I don't understand why you guys aren't doing the “model change.”
In my opinion, there's much less chance of something going wrong than when soldering around on the circuit board. 
You get axis labels, a counter that goes up to 240 MHz and a waveform recorder/player.
For free! 

[evava]

I did it like this. From the delivered version V1.0.1.0.13 (my device must have been way in the back of the warehouse...) I went straight to the version V1.0.1.8.2 that's distributed here. I haven't done any model change so far.
Works perfectly fine so far (not counting the still built-in hardware design flaws).

And what about the cursor issues goaty described—the ones that forced him to revert to the previous version?
You don't have those cursor problems?
See his picture in reply #1000 on page 41 !