I want a DSO but I am over whelmed by choice - Page 1
Forum section: electronics / testgear

author: Steve Zarg
author_rank: Contributor
timestamp: February 03, 2014, 03:16:37 am
content: Hi,I make DIY audio gear and I'd like a DSO so that I can experiment with some of my circuits. My interest is more or less confined to the audio spectrum but I want to be able to see waveforms in great detail.I started by looking at the really inexpensive models thinking that their range far exceeded my needs but I slowly came to realize that the better models didn't just have more range but they also had a better over all experience so I have slowly become interested in more and more quality.I know I would like a large display and I want to be able to make screen shots as my interest is in doing stuff like cataloging the effects of distortion on a test signal as different parameters on my audio gear are changed. I am also very interested in looking at linear power supply rectification and filtering. It seems like fairly simple stuff but I am interested in the tiny details.Having said that I was considering the OWON SDS7102 until I saw the video review that pointed out some of its details. Now I am attracted to the Rigol DS2072A. I know that in many ways it is over kill but the usability and build quality seems like stuff I will appreciate.In the mean time my wife has begun to take the hobby of Arduino seriously. She has lots of programming experience and just a little electronics experience but she is getting into motor control and switching. My electronics experience is analog audio and some digital audio. I'd like to buy a scope that she can learn to use and so I'd like to anticipate some of the needs she will have with high bandwidth applications. For example; will a 2 channel scope serve her well?We are members of a maker space that is just getting started and have access to some wonderful people that have lots of experience in electronics so it's a great time for me to get a DSO and learn from them.I'm lucky to be able to afford something like the Rigol DS2072A, but I'm wondering if it is over kill to the point of being foolish or if the impressive specs are just coincidental to the level where good build quality and ease of use starts entering the market. I really like good build quality and I usually regret spending money on stuff that reminds me I should have bought what I really wanted. :-)My current scope is an old Bell and Howell that uses vacuum tubes... it's old and funky. I've never really enjoyed using it.It's time to get something new.I'm hoping someone can offer some perspective and advice.Thanks.

author: echen1024
author_rank: Super Contributor
timestamp: February 03, 2014, 03:30:40 am
content: The DS2072 is not overkill. It's features, such as waveform intensity grading, can be appreciated by anyone, especially in audio. It offers a very long record length with segmented memory, and has a high waveform count to help you capture the rare glitches. Your wife will for sure appreciate the serial decode and triggering, which can be had free of charge thanks to some members of this forum. If you want 4 channels, the DS1074Z might be a good choice if your wife decides to work with SPI. Also, max budget and location would be helpful.

author: mrflibble
author_rank: Super Contributor
timestamp: February 03, 2014, 04:51:55 am
content: Allow me to end the overwhelmingness of it all.Round #1: DS1074Z or DS2072A.Round #2: DS1074ZThat was easy!This from someone who has worked with a 2 channel scope for years, and quite often thought "gee, I wish I has some extra channels".

author: cybermaus
author_rank: Frequent Contributor
timestamp: February 03, 2014, 08:27:40 am
content: Quote from: Steve Zarg on February 03, 2014, 03:16:37 amI am in love already.But seriously: I do have a DS1074Z-S, and its a very nice scope, but for that and SPI you want a logic analyzer. Not even a fancy one, PC connected is already better then trying it on a scope designed for analog signals. The scope is still useful where the arduino interfaces with the real world in analog, but those are usually again lower frequencies.

author: Steve Zarg
author_rank: Contributor
timestamp: February 03, 2014, 12:09:16 pm
content: Thanks for the replies and the suggestions.FWIW, we are in Florida, U.S.A. and our budget is flexible enough to allow me to seek out long term satisfaction.Thank you. I'll go look at the 4 channel model that was suggested... I assume that if you compare 2 channel to 4 channel at the same price that you take a step back ward in quality with 4 channel and like wise if you compare quality like to like that you take a step upwards in price to have 4 channels.What is the Rigol equivalent to the DS2072A?Thank You!

author: wilheldp
author_rank: Regular Contributor
timestamp: February 03, 2014, 12:24:57 pm
content: Quote from: Steve Zarg on February 03, 2014, 12:09:16 pmThe DS2072A is a Rigol.

author: Steve Zarg
author_rank: Contributor
timestamp: February 03, 2014, 01:43:42 pm
content: rephrase:What is Rigols 4 channel equivalent of the Rigol DS2072A.I went and looked through the range and from what I can see there is no direct like to like. You either drop in sample rate with the DS1074Z or lurch upwards to the DS4012.I've been under the impression that faster sample rates not only provide more detail but also provide snappier, low latency response, to adjustments made on the scope. The sample rate on the DS2072A seemed very attractive to me for that reason. I wonder if I have the correct impression or if I am mistaken about that.If the DS1074Z feels as responsive then I am going to give it serious consideration.

author: Rigby
author_rank: Super Contributor
timestamp: February 03, 2014, 02:03:00 pm
content: I have a DS1074Z-S and it is a good scope. I'm not sure why people think it's not a responsive scope, honestly. Unless I have the trigger point one full second off screen, which I did once, somehow, it is very responsive and seems to perform very well. It's a bit more fiddly than my analog scopes, but the advantages of a DSO are immense and I barely use the analog scopes anymore. Ironically (or maybe not), even though both of my analog scopes are 100MHz scopes, I use them for audio.The DS2072A can be upgraded to 200MHz, the DS1074Z to only 100MHz. The channel argument is dependent entirely on what you think you'll be doing. Beginners probably won't need to go beyond 100MHz unless they need to go well beyond 100MHz. YMMV.If you need a signal generator later, or if you think you will, getting the -S option of either would be worth it now. Not sure if the DS2000A-S is available yet, actually.Either of the Rigols would be good. I have a DS1074Z-S and I love it.

author: Steve Zarg
author_rank: Contributor
timestamp: February 03, 2014, 02:37:21 pm
content: It is not that I specifically think that the DS1074Z is unresponsive. I had not even considered that model until it was recommended here. It has been my general impression that digital scopes, by their nature, seem to have latency compared to analog scopes.In digital audio we have the same sorts of concerns where a driver running at 44.1kHz sample rate has more latency than the same hardware running at 96kHz.I don't have a practical reference for how a DSO feels.I really want a large display so I have confined my interest to looking at devices that have that feature. The Owon SDS7102 seemed very attractive until I learned how it utilized it's display space. I also read comments about latency, and comments about the feel of the buttons and build quality etc.I know that I don't need 4 channels for myself although I could have fun with it. I think the screen grab feature will allow me to make comparisons with higher res imaging if I want to work through gain stages and see where changes occur. I don't have the experience to know what my wife may appreciate in the near future as far as the number of channels but it occurred to me that she is already working on projects with multiple analog out puts where timing needs to be coordinated precisely.I got the impression from the comments above that because the Arduino has such a convenient connection to a PC that using a scope with Arduino projects will probably be focused on analog output where as someone working with controller chips without a convenient PC connection would be more likely to appreciate specific features in a DSO.So it seems to me that determining if responsiveness is appreciably different is as important as wondering if I or she will ever want the extra channels.I also have a thought about future expansion; Can two 2 channel scopes work effectively as one 4 channel scope?Finally, I want to point out that I haven't been thinking about the hacks I have read about. I just want to buy something and use what I buy. Keep it simple etc. It seems like the Rigols have great reputations as quality stuff and that is what got me looking at them with intent.Thank You.

author: Rigby
author_rank: Super Contributor
timestamp: February 03, 2014, 02:47:33 pm
content: Quote from: Steve Zarg on February 03, 2014, 02:37:21 pmNot really. There are usually only one trigger circuit per oscilloscope, meaning that whichever channel you're triggering on will be how all the other channels trigger. If you want to trigger on an intermittent pulse on channel 2, and you want to see a real-time sine wave on channel 3, thatis bestcan only really be handled with two scopes. Oddly, the aged Rigol DS1052E can do separate triggers, but no other modern scope can, that I know of.edit: rephrasing a bit to better answer your question: "Can two 2 channel scopes work effectively as one 4 channel scope?" The answer is "not unless you can trigger them together" if and only if you want all 4 channels on the same trigger. This can be done if you don't mind using the same trigger on two scopes, meaning that you're wasting one channel on one scope just to get the same trigger on both.You would definitely want a 4-channel scope if all four channels having the same trigger is important.If you want two or more separate triggers, then you will want two or more scopes.

author: echen1024
author_rank: Super Contributor
timestamp: February 03, 2014, 02:56:22 pm
content: I think you are in Agilent territory now. What about a DSOX2004? Or the MSO.

author: cyr
author_rank: Frequent Contributor
timestamp: February 03, 2014, 05:13:37 pm
content: Absolutely check out the Agilent if you have the money, value responsiveness, and want a four channel scope.

author: WVL_KsZeN
author_rank: Regular Contributor
timestamp: February 03, 2014, 07:11:32 pm
content: Quote from: Rigby on February 03, 2014, 02:47:33 pmYou can channel the trigger out of scope #1 into the trigger-in of scope #2.

author: Steve Zarg
author_rank: Contributor
timestamp: February 03, 2014, 08:11:05 pm
content: Thank you to every one for the comments and explanations.

author: Mark_O
author_rank: Frequent Contributor
timestamp: February 03, 2014, 11:51:02 pm
content: Quote from: Steve Zarg on February 03, 2014, 03:16:37 amI could chime in with some comments on scopes, but I think others have covered that territory pretty well. Instead, I'd prefer to suggest that what you might really need is not a DSO at all.Most here (not all) are working with signals well outside the audio range. So their recommendation bias will favor a scope. OTOH, your stated interest is not only in audio per se, but also in working with low-level signals, and determining very low levels of distortion. Frankly, DSOs aren't great for that use. Their residual noise levels are relatively high (~1mVpp), their accuracy poor (+/-2%... but offull scale, which will sometimes be unobtainable). This means their dynamic range is extremely limited. And while they do have FFT functions to look at signals in the frequency domain, they're pretty crude and low-accuracy. Lastly, noise sources in this arena tend to be very low amplitude. Low enough that a DSO may not even "see" it, much less be able to measure and quantify it.For what you've indicated, it may be worth your time to look at theAudioAsylumQuantAsylum products. They've got some really nice software, specifically designed for the tasks you mentioned. You may find they fit your needs a lot better, and provide you with the kind of results you really want.

author: Steve Zarg
author_rank: Contributor
timestamp: February 04, 2014, 01:11:46 pm
content: Thanks again everyone. I think the DS2072 seems like my preferred choice. When they get back in stock here in USA I'll give one a try. I started with the notion that a $400 scope would be great. I've doubled the budget with the idea that doing so provides great value. The $1200 famous maker scopes don't seem like the same sort of value and the next step seems to be $2000. It seems like $800 is a good place to start.Hi Mark,I went and looked at QuantaAsylum gear. It seems interesting and it caused me to realize that I hadn't considered bit depth resolution. I've been using 24bit (which seem to only really be 21bit) audio converters for years now so the idea that the DSOs use 8bit ADC seemed like an eye opener. I appreciate that the audio sample rates are much lower so I am starting to recognize how bandwidth has to be balanced with vertical resolution to manage a data rate on a DSO.It got me thinking. Half of my interest is in inspecting the peaks and transient edge of signal impulses so something like the DS2072A 500uV/div seems useful for that. The QuantAsylum USB scope was rated at 2mv/div. I wasn't sure if I should infer a direct comparison but it seems like it is applicable.The other half of my interest is searching for noise and digital hash on a DC rail so something with less self noise and better vertical resolution makes sense for that as all of that activity will be buried in the noise floor.I can see how will be easier for me to observe noise in my audio files at 24bit resolution and now I realize that it may be hard to find a tool that lets me trace down the source of the noise by working through the circuit behind the actual outputs.My enthusiasm for a DSO persists but now I see that I may want to augment the tool set with items specifically tailored to audio analysis. Thank you for pointing that out.

author: ot1
author_rank: Contributor
timestamp: February 04, 2014, 02:31:47 pm
content: Quote from: Steve Zarg on February 03, 2014, 02:37:21 pmWife into motor control = 4 channels, Steve = lucky! Think of the advantages when you get her a piece of test equipment for her birthday !! ... Just kidding get her a nice pair of leather boots instead.

author: agdr
author_rank: Unknown
timestamp: February 04, 2014, 04:20:41 pm
content: You actually do need a scope with 200+ mHz bandwidth for audio, to check for oscillations with some modern high-bandwidth "audio" low-noise low-distortion op amps. I just bought a Rigol DS2102 for audio use for that very reason. The 2102 has been measured with a 3dB point of around 175mHz which is close enough. The scope's internal front end chip has a 200mHz filter setting even though it is sold as a "100mHz" scope.For example, the LME49990 has a bandwidth of 110mHz and the LME49600 audio buffer you can wrap it around has a BW of 180mHz in high-bandwidth mode (or 110mHz in low-BW mode). So both chips could easily have spurious oscillations in the 100 - 200mHz range in-circuit. You would never even know without a scope with appropriate bandwidth.For a 4 channel version of the DS2000 series you would need to go to the DS4000 series, like the DS4024. 200mHz bandwidth, 4 channels, and a 4GS/s sampling rate vs. 2GS/s with the DS2000 series. Keep in mind for square wave edges, or fast rising peaks, you ideally want the sampling rate to be 10x or more to include enough Fourier components. So even though the Rigol DS2000 line has a 300mHz model, that may not be the best of ideas vs. going to a 4GS/s unit like the DS4000 series, if you want to look at things above 200mHz.I would echo Mark_O's comments about the QA400 audio analyzer box. Good stuff.Uses proprietary software which avoids the driver insanity with Windows. Or take a look at running ARTA on a soundcard, like the Juli@ or an old EMU-0204 if you can find one.I would agree with Mark_O about signal levels. That is another plus of the Rigol DS2000s. With modern audio op amps you often have input noise densities of 2nV/sqrt(Hz) or less, leading to an end-to-end system noise floor in the -120dBV to -140dBV range. The low vertical scale on the Rigol is only 500uV, but that is still better than many scopes which only have a minimum of 1mV - 2mV or so.For audio-band FFTs, if you want bit of a DIY project, you can make up that difference by whipping together a pre-amp using a low noise chip like the LME49990 or the OPA637 with a gain set to 30 or so and running from two 9V batteries (so as not to introduce line harmonics). Precede that with a sharp (Twin T) notch filter to filter out the fundamental (usually 1kHz or 10kHz) from your signal generator.

author: Mark_O
author_rank: Frequent Contributor
timestamp: February 04, 2014, 11:34:42 pm
content: Quote from: Steve Zarg on February 04, 2014, 01:11:46 pmQuantAsylum, yeah, that's the ticket!Sorry about the brain-fart with the AudioAsylum reference, but I haven't looked at their stuff in a while, and that was from memory.Glad you found them anyway.QuoteThat's true. Also, even 8-bits isn't always 8-bits. I.e., often you'll find the ENOB is more like 7-bits. And sometimes even less! So the dynamic rang that's available is relatively poor.QuoteIt's worth noting. However I'm not sure how useful that 500uV/div setting really is? If you look at screen-caps owners have posted at that sensitivity, with the inputs either open or grounded, there seems to be about 1 full division (aka, 500uV) of PP noise. I.e., while it's helpful to expand the trace vertically, anything less than 1 mV is going to be buried in noise. Though I suspect that averaging could help with that. Also, using the built-in bandwidth limiter could also reduce that noise as well. And if you want to focus on the 0-100kHz range, an external LPF may help out. Bottom line though, a clean 2mv/divmay bemore effective than a noisy 0.5mV/div.QuoteAgreed.QuoteOne possibility (which I have never explored) would be to use an external, low-noise/distortion preamp, to buffer and amplify your signals, before they hit the DSO front-end. Essentially, that's the approach high-end instrumentation systems use.Lastly, I commented on the FFTs these lower-cost DSOs offer, but failed to mention that part of their performance disadvantage is due to processing <1,000 points of data. Better units (Hameg, etc.) process up to 64,000 points, which improves the FFT resolution and results substantially.QuoteYou're welcome. One other possibility you may want to take a look at is CleverScope. 12 and 14-bit sampling. Along with some powerful software for analysis and visualization. Not close to cheap, though way less than big brand-names. But it may be good to see the types of things they can do, and see what can be replicated with cheaper options.

author: Mark_O
author_rank: Frequent Contributor
timestamp: February 04, 2014, 11:42:56 pm
content: Quote from: agdr on February 04, 2014, 04:20:41 pmThe DS1074Z, rated at 70 MHz, is really closer to 100 MHz at -3dB. "Modded" to the 100 MHz version, actual 3dB point is around 160 MHz.QuoteThanks. Yes, that's the type of thing I was thinking about above. I should have read ahead, before posting.

author: EEVblog
author_rank: Unknown
timestamp: February 04, 2014, 11:51:51 pm
content: Quote from: Mark_O on February 03, 2014, 11:51:02 pmNot the Rigol DS2000 series. It has 500uV/div range, and <500uV p-p noise floor @ 20MHz bandwidth

author: EEVblog
author_rank: Unknown
timestamp: February 04, 2014, 11:55:48 pm
content: Quote from: Mark_O on February 04, 2014, 11:34:42 pmYes, averaging helps a lot.QuoteIf you need signal measurement fidelity on mV or sub mV level signal, then a general purpose scope is not the right tool for the job. At the very least you'll need a pre-amp.

author: Mark_O
author_rank: Frequent Contributor
timestamp: February 05, 2014, 12:04:12 am
content: Quote from: EEVblog on February 04, 2014, 11:51:51 pmAgreed. That's why when I was referring toDSOs in general, I mentioned the 1mV. Re: the DS2000 specifically, I wrote, "If you look at screen-caps owners have posted at that sensitivity, with the inputs either open or grounded, there seems to be about 1 full division (aka, 500uV) of PP noise."I also suggested bandwidth limiting, averaging, and an external LPF can help in reducing that.EDIT: And I see now that you've agreed with my assessment of a GP scope, and a need for a pre-amp. So I think we're all on the same page.I really was just wanting to bring to the OP's attention the fact he was getting advice on general-purpose signal analysis devices, while his needs were more special-purpose. And that was achieved.