[Coco] WTB Orchestra 90 cartridge

[Jayeson Lee-Steere]

On audio, there are a lot of options about which caps are appropriate for
audio, but all references I have seen say that ceramics are not an
appropriate choice in the audio path. Given their strong piezoelectric
properties, it is not clear to me what are appropriate uses for the
recently available, high value MLCC ceramic caps. Too bad, because they are
smaller and less costly than tantalum.

This reference on audio caps seems fairly balanced:
http://sound.westhost.com/articles/capacitors.htm

Film capacitors are the thing to use where practical. It would seem some
film types are better than others, but for this use, polyester would be
more than sufficient. That is probably what the small value caps are in the
original Orch 90. Next down the line are electrolytics, which are
apparently fine for audio coupling if an appropriately large value is used.

Jayeson


On Mon, Aug 1, 2016 at 12:50 PM, Zippster <zippster278 at gmail.com> wrote:

> Hi Jim,
>
> Responses in-line…
>
> PCBs should arrive tomorrow, so hopefully we’ll find out how they work
> later this week.
>
> - Ed
>
>
> > On Jul 31, 2016, at 11:06 PM, RETRO Innovations <go4retro at go4retro.com>
> wrote:
> > A couple questions:
> >
> > * Looking at the schematic of the orch 90, it looks like 3 of the caps
> >   are non polarized electrolytic.
>
> I don’t want to open mine either, but I believe you are correct.
>
> > On your redesign, it looks like
> >   you swapped out for ceramic or something similar.
>
> Yes, I used just plain ceramics, which I suspect will be just fine here,
> but hey
> that’s what prototypes are for.  :)
>
> > Was there some
> >   reason why Tandy used the non polarized (I had not heard of them
> >   before perusing the schematic)
>
> I can’t think of one.
>
> > * The r2r ladder.  I assume the original resistor networks were 1/8W
> >   or 1/4W Did you go with 1/4W or 1/8W on the surface mount
> >   replacements?  Or, did you go with something smaller?
>
> Bourns isolated resistor arrays.  Rated  .16 W per resistor, so somewhere
> in-between.
>
> >
> >
> > I hate to open my sealed cart up, or I could probably answer part of the
> second question.  Anyone have hires pics of an open cart?
>
> There’s a pic in the folder here, but not very high resolution.
> <https://drive.google.com/open?id=0B1sgl615FlGnLWk1akpheXhCcWs <
> https://drive.google.com/open?id=0B1sgl615FlGnLWk1akpheXhCcWs>>
>
> >
> >
> > Jim
> >
>
>
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