how to buy a scope

Discussion in 'General Electronics Chat' started by disantlor, Jul 3, 2006.

  1. disantlor

    Thread Starter Member

    Jun 21, 2006
    20
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    I've been trying to find some information on what to look for in a scope but I'm still not really sure where to begin. I suppose I'll want a digital one as it would be helpful to have computer connectivity. Also, as I am most interested in audio applications, so I will need one that can handle up to 20khz but not much more. Finally, being a fairly poor college student, I'd like to not spend more than 200-300$ if I can, though I may be able to swing a little higher if it's worth it to do so.

    Any one have any suggestions on specific brands/models or at least a place I can go to find more information? Thanks!
     
  2. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
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    Microscope or Oscilloscope?

    What will you be using it for? Maximum frequency, type of signal ect.
     
  3. Papabravo

    Expert

    Feb 24, 2006
    9,905
    1,723
    Any scope you buy in that price range won't be worth the powder to blow it up. My advice is to save your nickels to buy one you can use, or convince your friendly neighborhood banker to make you a loan with the scope as collateral.
     
  4. disantlor

    Thread Starter Member

    Jun 21, 2006
    20
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    oscilloscope, and audio frequencies as I mentioned.

    I was afraid they would cost a lot more than that (200-300$). What kind of price are we looking at here? I don't need anything crazy, but I want to at least make a worthwhile investment.
     
  5. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    143
    Can you not look at getting a deal through your University? Whilst you still may be looking at more than what you suggest above, it will certainly be cheaper than buying one retail from a store.

    Dave
     
  6. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    check this out http://www.oscilloscopedepot.com/ they have an ongoing sale of what you want

    one advantage of a digiscope is you will be able to view the waveform again if you want to review it again. however whether you use an analog or digital it will do for many applications and besides you mentioned you're more on audio signals. for some specific task each has its advantage and disadvantage. some engineers prefer analog if they want to view the waveform of a rapidly varying signals in real time.

    moz
     
  7. disantlor

    Thread Starter Member

    Jun 21, 2006
    20
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    wow, the prices on some of those digital ones are frightening! I'm looking into the B+K Precision 2120B. Thanks for the link!

    I will look into getting one through school, that's a good idea, however I now go to music school (transferred from engineering school - doh!) so I'm not sure what my options will be.

    Thanks for all the help everyone!
     
  8. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
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  9. awright

    Well-Known Member

    Jul 5, 2006
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    You don't reveal where you are located, which can affect the resources available to you locally.

    I have been playing around in electronics for too many decades and have never owned a new 'scope. With a little care and time (which you may be short of as a student), you can probably find a very useful used 'scope in your price range at far less than the price of a new one. I don't think I have ever paid more than about $200 for a 'scope, and now have several (actually, an embarrassing quantity) of 'scopes including a couple of 100 MHz DSOs, several 20 and 50 MHz 2-channels, and a number of old Tektronix tube 'scopes (for nostalgia).

    Used equipment dealers, ebay, garage sales, auctions, classified ads, on-line listings, flea markets and flea market newspapers are all potential sources. But you are the only one who can protect yourself from a bad deal or a piece of junk.

    First, even working basically with audio frequencies, you need a 'scope with frequency response way above audio frequencies. You probably can't even find a 'scope with less than 10 or 20 MHz frequency range these days, and you wouldn't want to. And if you find a good deal on a higher frequency 'scope, don't pass it up. With digital circuits, switching power supplies, PWM audio amplifiers, searching for glitches, high frequency response is very valuable. You can't have too much frequency range unless you are paying a premium for it.

    As an old codger, I strongly recommend a regular analog bench 'scope as your first acquisition. They are easily portable and you can learn a lot and do a lot of work with them and they don't have the limitations and sampling anomolies of PC-based 'scopes. Until you have the experience to have some insight into what you should be seeing on the screen, you can easily fool yourself by a stable, clean, totally deceptive display on a PC based 'scope.

    Unless it is dirt cheap and you can afford to throw the money away, never buy a used 'scope that you cannot either get a written return privilige allowing you to thoroughly test the unit for a few days or you can take plenty of time before closing the deal putting the potential treasure through it's paces, open the hood (bonnet?) and inspect for burned components and circuit boards, burned insulation smells, amateur rapair attempts, corrosion, dirt, etc.

    NEVER buy a 'scope with a burned out CRT or power transformer! If you can get replacements at all, they can be much more expensive than a used 'scope is worth.

    Buying off ebay is a giant crap-shoot. I have gotten great bargains and I have been royally screwed, including plain old disappearing act by a seller and being sent a piece of equipment that looked like it had sat under a hay pile in a barn for a decade or two. My advice is to NEVER buy anything of high value off ebay unless you check the seller's feedback AND the listing states or you get an email stating that you can return the item if you find it unsatisfactory. Many sellers exploit the nature of the ebay market and the wishful thinking of buyers by stating, "I am too dumb to know how to test this item so it is sold as is, no returns." That generally means that they have thoroughly tested the item, found that it is unrepairable junk, and want to pass the burden on to the next sucker.

    Reputable used equipment resellers are sources of reliable instruments that have been professionally checked out, but you pay for the service and any warranty offered. Not my first choice, but at least you have some assurance of quality.

    Have fun.

    awright
     
  10. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
  11. disantlor

    Thread Starter Member

    Jun 21, 2006
    20
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    haha my question was more "how to buy" as opposed to "where to buy", but it does look like ebay is a pretty decent source for scopes.

    awright, thank you very much for the great post, helps me narrow down what I'm looking for greatly. It's hard to find what you need when you dont know what you need! So thanks again for that.

    By the way, I'm located in Boston, attending Berklee College of Music. I hear that MIT occaisionally has a used equipment sale when they dump old stuff they don't need, so I'm gonna check that out and now I'll know what I'm looking for.
     
  12. nethopper

    New Member

    Jul 22, 2006
    1
    0
    A sound Card based oscilloscope/spectrum analyzer/signal generator is just right for you.

    Nowadays, a sound card can support a sampling frequency of up to 192 kHz and have a bandwidth of 10Hz~50kHz.

    Taka a look at this website: http://www.virtins.com

    You can download and try the software called Sound Card MultiInstrument. It has a lot of functions only found in much more expensive instruments. It is good and cheap for any test & measurement in audio frequency range. It can measure a voltage even below 1 microvolt. With the probe it offers, it can measure a voltage up to 24V.

    The software is currently sold at only US$49.95. You can spend another, say $40 to buy a USB 24-bit sound card if your PC built-in sound card does not seem to be good enough for your application.
     
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