[Coco] WTB Orchestra 90 cartridge

[Jayeson Lee-Steere]

Thanks for checking John.

On Wed, Aug 3, 2016 at 10:16 PM, 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.
>
> Hth!
>
> John
>
> 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
> consideration
> > 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 10,000Ω 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 test,
> > at 12,000Ω.  One TV came in at 50K ohms, and everything else I could find
> > 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
> frequencies
> > 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.
> >
> > <
> http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=203424567&uq=636057666275979890
> <
> http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=203424567&uq=636057666275979890
> >>
> >
> > - 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 0.1uF
> > > non-polarized cap values. The smallest NP electrolytic I can find
> available
> > > anywhere is 1uF, and if you look at the pic of the Orch 90 board, what
> > > 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
> > > circuit?
> > >
> > > 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
> output
> > > impedance of the Orch 90 DAC is indeed around 1/100th of the  Coco 2/3
> > > circuits mentioned. Still, makes more sense to me than using a 0.1uF NP
> > > electrolytic where a 0.1uF polyester cap would do.
> > >
> > > Having the screw under the label sure is a curse, eh.
> > >
> > > Jayeson
> > >
> > > On Wed, Aug 3, 2016 at 6:47 AM, Zippster <zippster278 at gmail.com>
> wrote:
> > >
> > >> 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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> > > Coco at maltedmedia.com
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> >
> >
> > --
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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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