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Random measurements with an iMSO-104

Discussion in 'Currawong' started by currawong, Aug 31, 2011.
  1. Currawong Contributor
    Some months ago, I bought an Oscium iMSO-104 which attaches to an iPhone or iPad to turn it into an oscilloscope of sorts. My thought was that I could get some vague idea of what was going on with some of my equipment by measuring things. Vague indeed it has been as the main analogue probe is 50 Ohms, making it less than ideal for measuring anything digital and it picks up interference easily, resulting in less than a perfect picture. Here are some measurements I took on a whim of various things. Don't read too much into these graphs as the last time I used an oscilloscope was in elementary (primary) school!
    Test wave from an Audiophilleo 1 directly from the socket (white) and with a Canare RCA 75 Ohm cable + adaptor (green). The spurious bumps are from interference and should be ignored. The only thing I think is of note is the slightly rounded shoulder of the square wave after adding the cable.

    Square wave output of a digitally generated 1kHz signal from the Chesky Records Jazz sampler.
    Audio-gd Phoenix XLR headphone output, 1 channel, volume set at 26. 
    Stacker II:
    From my iPhone 4 headphone socket at full volume:
    From my iPod Classic 160Gb (original type "fat" model) headphone socket at ~55% volume:
  2. SP Wild
    Awesome Amos!
    I bring up square waves of digital communications and analogue/digital signals of sensors with a scope at work, but can't see myself lugging in my audio gear to perform the same.  Its fascinating to see the square waves - I think there is a lot of hidden information here.
    I wonder if ringing of the both the amp outputs could be sourced at the dac.  From what I understand, all oversampling dacs will have some form of ringing.  Would be interesting to have a NOS dac reproduce the square waves, the measurements on NOS dacs square wave published elsewhere show superior ringing control.  The ringing looks horrible on the Ipods, and I felt they sounded very glossy and artificially resonant at the upper frequencies very horrible.  Not unlike tube amps - which seem more glossy and resonant in the lower frequencies to me - but in that instance is a pleasurable distortion.
    I notice the stacker waves have a rounded "corner" in the top left of the rising square and bottom right of the falling signal.  Tubes are also said to round off clipping signals.  I can't explain it but every time I stick a tube in the signal of anything going into my HD650s or even HF2s - the treble sound more extended natural and smoother to my ears than with pure solid state equipment which comes off more grained in the treble, and its not the amp, because the LCD2s are smooth, fast and hits hard. 
    I wonder if these rounded corners take some of the physical stress away from the voice coil assemblies as they struggle to stop in time in doing so creating distortion noticed as grain to me, allowing them to operate more effectively within their physical constraints with a "soft landing" provided by tubes.  Perhaps planar assemblies have no such limitations and can stop as commanded without overshooting and causing distortions.
  3. Currawong Contributor
    I do gather that the ringing is normal thought I hadn't thought about its source. I was thinking about trying the output of various DACs, but they may be used to much higher input impedances than 50 Ohms, which I imagine is quite low.  I am DIY'ing a KGSSHV so I should be able to load things up with a spare resistor from all the parts I bought to simulate that. I also am thinking about finding or generating square waves of different frequencies. Especially for DACs, it would be very interesting.
  4. SP Wild
    If you do go ahead and establish more results, please report them.  I would be eager to view more of your findings.  [​IMG]

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