[Coco] It's a small win, but a win nonetheless

[Gene Heskett]

On Sunday 12 March 2017 15:05:59 RETRO Innovations wrote:

> On 3/11/2017 11:46 PM, Dave Philipsen wrote:
> > I guess the reason I'm so interested in your project is that over
> > the years I have used microprocessors to read and generate
> > data-on-tape for various projects including Teddy Ruxpin, Chuck E.
> > Cheese's, ShowBiz Pizza Place, SMPTE time code, and others.
> > Interestingly I have never played around much with the CoCo cassette
> > data though.
>
> And I hope my comments don't create an assumption I am upset at that
> fact.  On the contrary, I am excited that someone else finds my
> exploration of interest.  Happy to send schematics and such if you're
> interested in looking or helping.  All my projects are CC (hardware)
> and GPL (software/firmware), so anyone can enjoy.
>
> To add some additional color, the sine wave coming out of the Coco1 is
> a thing of beauty.  nice and rounded and smooth.

Thats because the driver op-amp was too slow, and slew rate limited. 
Which is why it MUST be replaced with something considerably faster for 
drivewire to work at a usable speed.

> I didn't pay a lot of attention to the Coco 2 waveform, but the Coco3
> was jerky, sharp, and seemed unfiltered.  Cost reductions and
> integration evident.

Faster op-amps in the 2 & 3's.  The source of that waveform, assuming 
light speed parts is a 3 bit d-a, generating a 5 level approximation of 
a sine wave.  The speed of the parts rounded it off to something a cheap 
cassette recorder could handle w/o aliasing if it had a bias circuit, 
most didn't. Excellent white noise generators without the ac bias and 
erase circuitry. Also often responsible for doing a multipass erasure of 
your data tapes.

>
> Jim


Cheers, Gene Heskett
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