# Through Zero FM with the 3340

**URL:** <https://lookmumnocomputer.discourse.group/t/through-zero-fm-with-the-3340/3257>\
**Category:** KOSMO MODULES\
**Created:** [March 28, 2021, 9:39pm UTC](https://lookmumnocomputer.discourse.group/t/through-zero-fm-with-the-3340/3257 "2021-03-28T21:39:35Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![BlackDeath](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/blackdeath/32/7644_2.png) [@BlackDeath](https://lookmumnocomputer.discourse.group/u/BlackDeath)\
**Post date:** [March 28, 2021, 9:39pm UTC](https://lookmumnocomputer.discourse.group/t/through-zero-fm-with-the-3340/3257/1 "2021-03-28T21:39:35Z")

</div>

There’s been some chat in the CAKE thread about Through Zero FM - to oversimplify, FM that stays in tune. Turns out that this is actually possible with our beloved 3340, with “[a bit of extra circuitry](https://learningmodular.com/understanding-the-differences-between-exponential-linear-and-through-zero-fm/)”.

I found this as an example:

 ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/d/d093cd033d27bc2210cfbdd84eb7661832b119dc.png)

from here: [Juergen Haible](http://jhaible.com/legacy/tonline_stuff/hj_modul.html)

It’s a bit rich for my blood, but I thought I’d share it as a point of interest for anybody looking to explore this more.

---

<div class="post-metadata">

**Author:** ![analogoutput](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/analogoutput/32/29663_2.png) [@analogoutput](https://lookmumnocomputer.discourse.group/u/analogoutput)\
**Post date:** [March 28, 2021, 9:49pm UTC](https://lookmumnocomputer.discourse.group/t/through-zero-fm-with-the-3340/3257/2 "2021-03-28T21:49:53Z")

</div>

At the risk of blowing past the topic in the second post, a couple of op amp through zero designs are these:

[http://ijfritz.byethost4.com/sy\_cir16\_teezer.htm](http://ijfritz.byethost4.com/sy_cir16_teezer.htm)

[https://www.haraldswerk.de/VCO/Trapezoid/Trapezoid\_VCO.html](https://www.haraldswerk.de/VCO/Trapezoid/Trapezoid_VCO.html)

(and another version of the latter [here](https://www.haraldswerk.de/VCO/Trapezoid_flat/Trapezoid_flat.html))

---

<div class="post-metadata">

**Author:** ![BlackDeath](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/blackdeath/32/7644_2.png) [@BlackDeath](https://lookmumnocomputer.discourse.group/u/BlackDeath)\
**Post date:** [March 28, 2021, 9:56pm UTC](https://lookmumnocomputer.discourse.group/t/through-zero-fm-with-the-3340/3257/3 "2021-03-28T21:56:05Z")

</div>

Gerbers and everything, nice!

---

<div class="post-metadata">

**Author:** ![fredrik](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/fredrik/32/682_2.png) [@fredrik](https://lookmumnocomputer.discourse.group/u/fredrik)\
**Post date:** [March 29, 2021, 2:23am UTC](https://lookmumnocomputer.discourse.group/t/through-zero-fm-with-the-3340/3257/4 "2021-03-29T02:23:27Z")

</div>

> [@BlackDeath](#):
>
> It’s a bit rich for my blood

The “thru zero” bit is the rectifier and the zero crossing circuitry (two comparators and a couple of XOR gates) in the lower right corner.

(so you could make this entirely optional, maybe even via a daughterboard).