[Coco] WTB Orchestra 90 cartridge

RETRO Innovations go4retro at go4retro.com
Wed Aug 3 11:38:13 EDT 2016

   Since you have the unit open, can you determine the voltage rating on
   the orange rectangular caps (There should be 2 .1uF ones and 2 .047uF
   ones)?  The schematic does not show a voltage rating on those.

   Also, the legends and marking on the SIP resistor and the DIP resistor
   network would help Zippster out as well.  The wattage and precision for
   those networks are not marked on the schematic either.


     On August 3, 2016 at 10:16 AM "John W. Linville"
     <linville at tuxdriver.com> wrote:
     The Orch-90 card I have opened has NP electrolytics exactly as in
     the schematics, 1uF @ C7 and 0.1uF @ C9 and C10.
     On Wed, Aug 03, 2016 at 07:39:10AM -0500, Zippster wrote:

     Yes, I'm reluctant to open the one Orch 90 cart I have here as well.
     I've been wondering about the choice in value as well.
     Using .1uF does seem like a really low value, until you take into
     that the output cap, in conjunction with the input circuit on the
     receiving end
     form a high-pass filter. To see what the effects of the value chosen
     will be,
     we need to know what that load impedance will be.
     What I can gather on the internet indicates it is typically 10,000W*
     or more,
     at least for typical consumer gear, and walking around the house
     with a multimeter
     here would seem to confirm that.
     The lowest I could find were the small speakers shown in the CoCo2
     at 12,000W*. One TV came in at 50K ohms, and everything else I could
     ran into many, many megohms.
     So, in a worst case scenario (10K), you're looking at a -3dB roll
     off of ~159Hz
     using a .1uF output cap. At megohm input impedances, it's
     negligible, certainly
     beyond the range of human hearing (mine at least), and wouldn't
     really matter.
     If the schematics are correct at .1uF, I almost suspect Tandy might
     have intended
     the high-pass formed from the connection to aid in filtering out low
     Hz noise,
     but who knows. The other consideration I suppose would be just what
     is this circuit even capable of producing.
     I may bump the value up of the output caps to something like 10uF or
     more on
     the final revision, not sure. BTW, I was able to find .1uF bi-polar
     electrolytic caps
     at Digikey.
     - Ed

     On Aug 3, 2016, at 4:51 AM, Jayeson Lee-Steere
     <cocolistemail at titaniumstudios.com> wrote:
     Very cool Ed.
     On capacitors, I think perhaps the schematic is in error with the
     non-polarized cap values. The smallest NP electrolytic I can find
     anywhere is 1uF, and if you look at the pic of the Orch 90 board,
     should be the 0.1uF NP caps are physically larger than what is
     supposed to
     be a 1uF NP cap. And then there is the question of, if 0.1uF is the
     intended value, why not use polyester caps as was done with the
     opamp input
     In fact, the caps look suspiciously like the polarized 10uF bypass
     cap on
     the 5V rail. This happens to be the same value as the output cap
     used for
     Tandy's Coco 2 and Coco 3 audio out. Not the best evidence since the
     impedance of the Orch 90 DAC is indeed around 1/100th of the Coco
     circuits mentioned. Still, makes more sense to me than using a 0.1uF
     electrolytic where a 0.1uF polyester cap would do.
     Having the screw under the label sure is a curse, eh.
     On Wed, Aug 3, 2016 at 6:47 AM, Zippster <zippster278 at gmail.com>

     >> Thank you. :)>>
     >> After playing some tunes in your CoCo, you can just flip the
     switch and
     >> plug it into a Dragon. Thanks to Pere Serrat's adaptation of the
     Orch 90
     >> ROM.
     >> <https://drive.google.com/open?id=0B1sgl615FlGnNzRhNC1xSjRBSFk <
     >> https://drive.google.com/open?id=0B1sgl615FlGnNzRhNC1xSjRBSFk>>
     >> Just plugged into the TV speakers, but you can see it works...
     >> - Ed
     >>> On Aug 2, 2016, at 5:38 PM, Bill Pierce via Coco
     <coco at maltedmedia.com>
     >> wrote:
     >>> <Applause> Good job!
     >>> Bill Pierce
     >>> "Charlie stole the handle, and the train it won't stop going, no
     way to
     >> slow down!" - Ian Anderson - Jethro Tull
     >> --
     >> Coco mailing list
     >> Coco at maltedmedia.com
     >> https://pairlist5.pair.net/mailman/listinfo/coco

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     John W. Linville Someday the world will need a hero, and you
     linville at tuxdriver.com might be all we have. Be ready.
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