[Coco] WTB Orchestra 90 cartridge
John W. Linville
linville at tuxdriver.com
Wed Aug 3 10:16:19 EDT 2016
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 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
> > --
> > 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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