[sdiy] DsPIC timer issue when used as DCO!

[karl dalen]

> This is very interesting. But I've
> done quite a bit of work building DCOs with the dsPIC
> timers, so perhaps it's just me.

Well then you should be able to detect the problem if there are any?
Could'nt you just set up a dspic timer and toggling the timer register?
It would be detected with square waves aswell.

How did Dave implemet the sync? fast ISR resetting count? I bet the sync on p08 do not sound the same as 3340 sync close but with a character. 
 
> This shows a square-wave LFO modulating one of the DCOs.
> The pitch glitch only seems to happen going up. Coming down
> is fine, as far as you can tell from this. We also need to
> think about how the triangle wave is generated. Is this a
> standard ramp-core DCO, followed by a triangle waveshaper,
> or is this a triangle-core DCO?

It's just a simple linear ramp current source with a shaper afterwards.

Mind you the 3396 and PA397 are one of the cheapest chips Doug made according to sources, and you can find traces of this in other datasheets of his, for example mentioning that out stage VCAs are basically 3080
types, but by reading and actually bredboarding with the 3396 you will
find the vast range of tollerances displays this is a affordable 
(sales managemet talk) chip and that was the goal for it.
Every parameter calibrated by a computer makes it decent.

The 3396 has an design bug in one of its out VCAs.


 


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