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Re: [SpectrumLabUsers] EMU0202 ground lifter

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  • ehydra
    ... Another guy sent it to me, thanks. The manual itself is not more helpful but recognize that in the spec sheet they explicitly say: differential ADC ! ...
    Message 1 of 12 , May 15, 2012
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      Alan schrieb:
      > ----- Original Message -----
      >
      > Subject: Re: [SpectrumLabUsers] EMU0202 ground lifter
      >
      >
      >> You can't disconnect the lower impedance gound and leave the signal
      >> alone. This is the best way how to destroy the input stage.
      >>
      >> Use a transformer to isolate the input from any ground-loop. I use
      >> common-mode ferrite chokes for this.
      >> I tried the EMU0202 download link but it is gone.
      >
      > Did this not work?
      > http://support.creative.com/manuals/download.aspx?nDownloadId=11575&prodName=0202_USB_Web%20manual
      > Click on "Agree" at the bottom and wait.

      Another guy sent it to me, thanks. The manual itself is not more helpful
      but recognize that in the spec sheet they explicitly say: differential ADC !


      > Or this link seems to go straight to it.
      > <http://ccftp.creative.com/Manuals/TSD/11575/0x6FF24E6A/0202_USB_Web_Manual.pdf>
      > They talk about breaking the ground loop.
      > Form your own opinion. What do the switches do? As I tested there is a
      > resistive leak to dissipate any static but there is no direct connection
      > from the input ground when the switches are operated. Creative give no
      > warnings so I presume they do no consider damage is likely.
      > Removing ground loops involves leaving just one low impedance ground.

      For audio people a "ground loop" is the 50/60Hz tone they recognize.
      They don't care about current or voltage. The problem is a voltage shift
      between two devices from a very low impedance loop. If the switch is
      opened, the current cannot circulate anymore but then you have a bigger
      voltage between BOTH inputs of the differential input AND ground!!
      Because the input is differential as long as the common input range is
      not exceeded the effective voltage at the ADC or OpAmp stage is then
      substracted and so zero.

      What I try to say: I think we say the same but with different words!

      When the switch is open in the technical circuit sense, probably
      something like 100K // 1nF is effective between case ground and one of
      the differential inputs, otherwise shortened.

      Maybe someday I will make a circuit diagram of important parts of the
      EM0202 here. I wonder that I didn't found any try at the web.


      Another interesting point is that this sound-card switches the cut-off
      frequency of the analog input stage low-pass filters according of the
      chosen sampling frequency. Maybe not in the 192KHz case but in the lower
      sampling frequency options.
      So if you choose lower bandwidth the S/N should go a little higher.


      > Transformers should not be necessary, maybe they help but can cause other
      > problems especially if you are using frequencies up to 96KHz..
      >

      I don't see any intermodulation distortion but didn't investigated this
      very careful. Interesting question when the ferrite will go crazy??

      Most times the scope is the only ground here.


      >
      > They show a newer(?)
      >> device, the 0204. Any idea what is newer there? Better ADC/DAC?
      >
      > I do not know, does it say on the Creative site?
      >

      Not amused to see all the marketenderizing ;-) So just leaved the site.


      - Henry

      --
      ehydra.dyndns.info
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