Through Zero FM with the 3340

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”.

I found this as an example:

from here: Juergen Haible

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.


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

(and another version of the latter here)


Gerbers and everything, nice!

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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).

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