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Thread: Looking for Tarbell Cassette Interface Schematic

  1. #11
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  2. #12

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    Hi Al,

    If I could bother you again just once more... On page 12 of the PDF, is the smudge at the bottom of the schematic for the modification present on your hardcopy as well? I assume that resistor there is just acting as a pullup for the last two pins of the 74L30? I'd like to make my implementation of this board jumper selectable between the two tape formats.

    Thanks,
    Alex

  3. #13
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    Quote Originally Posted by ab0tj View Post
    Hi Al,

    If I could bother you again just once more... On page 12 of the PDF, is the smudge at the bottom of the schematic for the modification present on your hardcopy as well? I assume that resistor there is just acting as a pullup for the last two pins of the 74L30? I'd like to make my implementation of this board jumper selectable between the two tape formats.

    Thanks,
    Alex
    it it missing on the original

    i think it's pretty safe to say it is pulling up the unused inputs

  4. #14

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    Ok. Thank you for checking.

  5. #15

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    Anyone bored and want to check over my schematic? It doesn't match the one in the manual exactly but as far as I can tell it should work as is. I changed a couple of parts to avoid hard to find* parts where possible, but was not able to find suitable replacements for the 8T20 or 7496 chips. I also added Tarbell's modifications to (hopefully) make the board switchable between the Tarbell and Kansas City standards, and added a relay to support operating the tape deck's Remote input.

    Corrections and suggestions are welcome.

    https://drive.google.com/file/d/0B86...ew?usp=sharing

    *As in, I typed the part number into the Jameco website and it didn't come up. All of the parts were still found after a short eBay search, although at vintage pricing.
    Last edited by ab0tj; August 18th, 2017 at 08:53 AM. Reason: Hmm, helps to add the schematic to the post.

  6. #16
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    Quote Originally Posted by ab0tj View Post
    Anyone bored and want to check over my schematic? It doesn't match the one in the manual exactly but as far as I can tell it should work as is. I changed a couple of parts to avoid hard to find parts where possible, but was not able to find suitable replacements for the 8T20 or 7496 chips. I also added Tarbell's modifications to (hopefully) make the board switchable between the Tarbell and Kansas City standards. I also added a relay to support operating the tape deck's Remote input.

    Corrections and suggestions are welcome.
    I suppose it wouldn't be as much fun, but couldn't you just do this with a microcontroller and maybe an op-amp on the input for gain control?

    if not, there are hundreds of 8T20s available here
    www.ebay.com/itm/221607581167

    you can replace the 5 bit shift registers with functionally equivalent 8 bit ones, and get rid of the 7474s at the end of the chain

  7. #17

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    Quote Originally Posted by Al Kossow View Post
    I suppose it wouldn't be as much fun, but couldn't you just do this with a microcontroller and maybe an op-amp on the input for gain control?

    if not, there are hundreds of 8T20s available here
    www.ebay.com/itm/221607581167

    you can replace the 5 bit shift registers with functionally equivalent 8 bit ones, and get rid of the 7474s at the end of the chain
    Agreed, a microcontroller and a small amount of glue logic would do the job just as well, perhaps even better with the right programming. That project would be fun in its own way but also doesn't have quite the same vintage appeal to it...
    I did already secure some 8T20 and 74LS96 chips, but I'd like to make this board available to the s100computers group if there is interest, so I'll look into using commonly available 8-bit shift registers. One less part for other builders to have to track down on eBay. Thanks for the pointers.

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