Bitscope

[tiroth]

Is anyone familiar with the Bitscope? This seems to be a very inexpensive DSO. ($250 as a kit, $350 assembled, even cheaper potentially as DIY)

It seems attractive to me because there are already some clients for it that support some rudimentary spectrum analysis (Scopal). $250 for a scope that can go 70MHz+ starts REALLY looking good when it also does spectrum and logic analysis.

I'm aware of the issues related to subsampling, but I'm concerned about the noise floor (unspecified) as well as the the lowest input range. It seems that for audio use a pre-amp may be necessary to get useful S/N and distortion measurements.

Anyone ever used one? Have any comments on the design even if you haven't? I must warn the uninitiated that the site is rather poorly designed in some ways and some sections (FAQ) are out of date.

[JonMarsh]

I don't think I can emphasize this enough (and I'm not trying to be snotty or anything (maybe it comes naturally! )

*Don't* plan on using an inexpensive digital scope type thingie for working on audio circuits!

At home I have a couple of Tek analog scopes, and other than not being able to do waveform capture, they work very well for looking at what's going on, including sorting out the difference between LF noise, HF oscillation, etc. This is surprisingly hard to do on most digitial scopes.

I also have a Tek TDS 754D, which with it's very wide bandwidth and sampling rate (continuous) and it's "digital phosphor" function is just OK for working on audio gear or SMPS. Of course, with it's capture and data saving modes, and built in hard disk, it's great for documenting stuff. And you can dump the measured data into MathCAD, and get something meaningful with FFT (up to 10 bits), if you're using the hi res capture mode. But 10 bits isn't much.

If I could only have one scope, and had a limited budget, look for a good used analog scope. It will tell you far fewer lies, and give you more truth. As for digital, Fuggetaboutit!

Re disortion analysis on a budget, think used HP or Tek or whatever. I have a Crown IMA and an HP8903- just don't lull yourself into thinking low THD or IM with lots of feedback is the bees knees.


Just my 0.02.

Best regards, and good luck with your projects.

-Jon

[tiroth]

Actually, I have a 10MHz analog scope. I've also done some experimentation with soundcard-based distortion analyzers and been fairly impressed by the result, although the quality of the hardware is often limiting. That's why the bitscope seemed attractive to me...it costs only a little more than a quality sound card and also supplies me with a lot of additional bandwidth.

[dice45]

tiroth,





thanx for the link. Scanned thru it, very impressive.


However, have to agree that an analog scope is a must as it will definitely show you what is happening, it will not produce artifacts.


Having said that, i love to aditionally have a DSO for it's comfort and its FFT, data acquisition, hardcopy possibilities etc.


I own a Fluke 123 which is being close to be undestroyable by high voltages (makes sense for tube ampifiers ). I plan to record tube charcteristics with it and then plot plate characterstics from the generated value tabulars. I use an AutoLISP routine to have AutoCAD plot the curves and then i can apply graphical evaluation methods e.g to determine operating points or calculate THD.





The bitscope has a stunning performance and can be easily programmed; i haven't seen anything comparable at this price so far.


I am sure the curve plotting described above could be done with it better than with my Fluke. Particularly FFT options could be very interesting.





I might get tempted to add it to my instrument collection as soon as i can afford it.

[planet10]

Originally posted by dice45
I plan to record tube charcteristics with it and then plot plate characterstics from the generated value tabulars.

I was thinking about doing the same sort of thing with Mac-the-Scope . I'll use Trapeze to generate the curves.

I also need to figure out automatic complex impedance capture for speakers.

dave

[ergo]

You could also consider Velleman kits/products if they are available at your location.

http://www.velleman.be/productlist2.asp?lan=1&id=347914

They have 13MHz and 50MHz scopes that go to your pc's LPT port and are software driven and they also have a 0-1MHz function generator.

The price of the generator kit here in Estonia is about 130USD and 13MHz scope for 150 USD, but this setup would provide you means for FFT analysis up to 1MHz and freq/phase bode plot automated measurement !!! The last is mainly why I'm also considering purchasing it.

Ergo

[Altaic]

I was wondering if anyone could follow up on the Bitscope-- did any of you get one? I'm in the market for an o-scope, and if the Bitscope does the job, I'd rather get it than a Tektronix, I think. But if it does create artifacts and such like most DSOs, I'd have to go analog.

Will

[hifiZen]

I couldn't agree more with the above posts. For that kind of money, you can get yourself a very nice analog scope with the bandwidth to handle what you want. I looked at similar circuits some time ago, and got myself a used 150MHz Tek scope instead - a FAR more useful tool!

One of the problems with bitscope and similar designs is that they don't have a high enough sample rate, instead relying on multiple-pass sampling of a repeating waveform in order to get the necessary resolution. This has it's own set of problems apart from the usual problems with digital sampling scopes. Even the best digital scopes which use proper full-rate sampling like the Tek DPO types still have a lot of artifacts and display quirks, and I don't like working with them unless I need to capture a waveform. At home, if I need to document a waveform, I'll take a picture of my analog scope screen with my digital camera. For FFT stuff, you won't need all that bandwidth for audio work anyway, so you may as well stick with your soundcard.

[tiroth]

Yeah...although I haven't made the plunge yet, I decided I'd be much better off getting a fast Tek mainframe.

[Altaic]

Five minutes before you posted I bought a tek 475 oscope w/ tek probes for $200 on ebay. It does 200MHz and should be ideal. =)

Perhaps when the Bitscope does 1GHz, I'll give it a go. Tektronix DSOs all do 1GHz+, and from what I've heard they are quite good.