[sdiy] Thru-Zero, was as3340 PW/tuning issue

[ColinMuirDorward]

Hi Adam,
TZ fm is more like what you get in a digital FM synth.
On a regular VCO, when the FM input goes to negative, what happens to the
VCO frequency? I think it either stops, or simply bounces back to the
positive domain. For this reason, you get some harsh harmonics (which can
sound great).
A TZvco handles the incoming negative FM differently. It reverses the VCO's
direction. Or, another way to think of it is that it flips the phase of the
VCO. This gives that nice Chowning style FM that we know and love.
Someone else might chime in with a more accurate explanation... I could
have butchered it.
Just waiting for alfa rpar to produce an economical TZvco chip, then we can
all get familiar and know it by ear.
Colin


On Sat, Jan 4, 2020 at 6:25 PM Adam Inglis <21pointy at tpg.com.au> wrote:

>
> Thanks Colin
> Someone in that thread says they would love a "through-zero version”.
>
> Seems to be a lot of talk about TZ all over these types of forums - why?
> What’s the big deal? How are these different from the VCOs in my Roland,
> Korg and Sequential synths?
>
> Sure I could google but I know I’d get better education here ;-)
>
> Adam
>
>
>
> On 5 Jan 2020, at 6:26 am, ColinMuirDorward <colindorward at gmail.com>
> wrote:
>
> Just a note to say thanks to everyone contributing to this conversation.
> I've applied lots of what I learned here to my design, and I've got the
> PWM/pitch interaction down to what I think is an acceptable minimum.
> Anyways, it's nothing special, but I've started a build thread over at
> muffs <https://www.muffwiggler.com/forum/viewtopic.php?f=17&t=225670>,
> for anyone who needs yet another low cost 3340 vco. I need several, so
> thought I may as well go public in case anyone else does, too. I'll be
> using JLCPCB assembly for all the resistors and caps, and the rest will be
> through hole at home. I have lots of as3340s, so can include with the PCB
> if anyone needs. 3340 is running on +10/-5, so the circuit should be at
> home in 12v or 15v setups. I'm in Yukon, Canada.
> Thanks,
> Colin
>
> On Fri, Jan 3, 2020 at 12:39 PM David G Dixon <dixon at mail.ubc.ca> wrote:
>
>> The Intellijel Rubicon (and Rubicon-2) gives the option of generating
>> pulse waves from Triangle, Saw, or Double-Saw (twice the frequency).  It’s
>> not a whole synth, just a TZFM VCO.
>>
>>
>> ------------------------------
>>
>>
>>
>

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