[Coco] WTB Orchestra 90 cartridge
John W. Linville
linville at tuxdriver.com
Wed Aug 3 14:06:10 EDT 2016
On Wed, Aug 03, 2016 at 11:38:13AM -0400, RETRO Innovations wrote:
> 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.
Sorry, they don't seem to have any such markings -- '473 T' and '104
"S"'. I think the T and S indicate tolerances.
> 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.
The DIP 20Ks are marked L2038 and the SIP 10Ks are marked 1038H. Both are
marked "IAM", which I presume to be the manufacturer -- unsure.
John
>
> Jim
>
> 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.
> 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 10,000W*
> 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
> test,
> at 12,000W*. 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=20
> 3424567&uq=636057666275979890
> <http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=20
> 3424567&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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> --
> 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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--
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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