[sdiy] SAW core VCO flyback time

[Tom Wiltshire]

On 31 Aug 2016, at 07:33, Andrew Simper <andy at cytomic.com> wrote:

> Totally agree here Don, but one thing left to talk about is PWM. I
> have noticed that on a lot of Tri cores the Sqr is derived from the
> Tri, not the Saw, is there any reason for this? If you use the Tri you
> can't get that lovely PWM vibrato sound. In fact perhaps even have a
> switch so you can pick between Saw or Tri for the source of the Sqr.

A switch would be nice. The triangle-based PWM is probably seen as an "improvement" since it doesn't cause the pitch warble you apparently appreciate!

> There is still the downside of traditional hard sync, yes David
> "interesting" is great but what if you want regular old hard sync? How
> much hassle would it be to implement a regular hard sync on a Tri
> core?

Not very difficult. The CEM3340 was a triangle core and included two inputs for "interesting" sync options. In practice, they weren't used much as manufacturers wanted the regular hard sync sound. Getting that sound added a transistor to the schematic.

> If you could get regular PWM and hard sync from a Tri core then it
> does sound like the way to go. Then for all those people that love
> buzzy Tris they can add a pulse to get it.

If you've derived a sawtooth from your triangle already, you can always use that to get your PWM sound. So what the core is doesn't need to affect how you do PWM - that's just a decision you make. Hard Sync is marginally more tricky on a triangle core, but just barely.

Tom