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Old VIP getting going after many years! Help with audio...

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  • DougCrawford
    Hi! Its my first post here! I m on the other Cosmac elf group too, but this is VIP specific. So I was kindly given a lovely VIP and just started working with
    Message 1 of 2 , Jan 7, 2013
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      Hi! Its my first post here!

      I'm on the other Cosmac elf group too, but this is VIP specific.
      So I was kindly given a lovely VIP and just started working
      with it yesterday.
      After reseating the chips its running reliably and am having some amusement peeking and poking stuff in that spacious 2KBytes.
      So now I'm testing save and load.
      I have it sort of working.

      Its a 2K machine, and I'm saving all 8 blocks.
      I had written COSMAC in the video memory as per the manual,
      and had put in the short blink test routine.
      I'm recording to AUDIGY on a laptop right now using the
      built in audio interface. I do have an M-AUDIO USB interface
      I can switch to if needed.

      I recorded the memory twice; one at rail-rail amplitude
      and one at about 70%. But I can't seem to get consistent results.
      Of course there are three variables: the recorded level, the Audigy playback level, and the sound card level... so adjustments are non-trivial!

      I have had the most success with the 70% but not total success.
      When it does complete the load with no Q LED error,
      its not quite right. The COSMAC graphic has never been recovered on load exactly right. Its shifted and not quite right. Its wrong the same way every time. When I get that far, the blink test at the start of memory does function.

      So some memory is getting filled up correctly, perhaps most of it.
      What seems to be a fundamental problem is that the signal on
      TAPE OUT, at idle, is VERY noisy.
      So I'm wondering if that's THE fundamental problem, and the first
      thing to try to improve. Its not just hum, it sounds like a
      lot of digital noise coupled in.

      If anyone is interested I can get a screen shot of this noise in
      AUDIGY or upload a short wave file of it for someone to checkout.
      Has there been an improved circuit developed to get a cleaner
      signal traveling down the TAPE OUT wire?

      This is important because I think for the foreseeable future audio
      transfer is going to be my only program save/load mechanism.
      Though I might take on some mods to allow load up direct from a digital source.

      Thanks!
    • DougCrawford
      FYI, my 70% amplitude wave file loads into emma2 just great! ... even though the real machine seems to not do so well as described before.
      Message 2 of 2 , Jan 8, 2013
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        FYI, my 70% amplitude wave file loads into emma2 just great!
        ... even though the real machine seems to not do so well as
        described before.

        --- In rcacosmac@yahoogroups.com, "DougCrawford" wrote:
        >
        > Hi! Its my first post here!
        >
        > I'm on the other Cosmac elf group too, but this is VIP specific.
        > So I was kindly given a lovely VIP and just started working
        > with it yesterday.
        > After reseating the chips its running reliably and am having some amusement peeking and poking stuff in that spacious 2KBytes.
        > So now I'm testing save and load.
        > I have it sort of working.
        >
        > Its a 2K machine, and I'm saving all 8 blocks.
        > I had written COSMAC in the video memory as per the manual,
        > and had put in the short blink test routine.
        > I'm recording to AUDIGY on a laptop right now using the
        > built in audio interface. I do have an M-AUDIO USB interface
        > I can switch to if needed.
        >
        > I recorded the memory twice; one at rail-rail amplitude
        > and one at about 70%. But I can't seem to get consistent results.
        > Of course there are three variables: the recorded level, the Audigy playback level, and the sound card level... so adjustments are non-trivial!
        >
        > I have had the most success with the 70% but not total success.
        > When it does complete the load with no Q LED error,
        > its not quite right. The COSMAC graphic has never been recovered on load exactly right. Its shifted and not quite right. Its wrong the same way every time. When I get that far, the blink test at the start of memory does function.
        >
        > So some memory is getting filled up correctly, perhaps most of it.
        > What seems to be a fundamental problem is that the signal on
        > TAPE OUT, at idle, is VERY noisy.
        > So I'm wondering if that's THE fundamental problem, and the first
        > thing to try to improve. Its not just hum, it sounds like a
        > lot of digital noise coupled in.
        >
        > If anyone is interested I can get a screen shot of this noise in
        > AUDIGY or upload a short wave file of it for someone to checkout.
        > Has there been an improved circuit developed to get a cleaner
        > signal traveling down the TAPE OUT wire?
        >
        > This is important because I think for the foreseeable future audio
        > transfer is going to be my only program save/load mechanism.
        > Though I might take on some mods to allow load up direct from a digital source.
        >
        > Thanks!
        >
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