[sdiy] DC-1 MHz, through-zero FM, controlled, oscillator without core capacitor

[Gordonjcp]

On Wed, Dec 03, 2025 at 09:46:24AM +0100, cheater cheater via Synth-diy wrote:
> what is the minimal analog implementation of a PLL that would be
> useful for taming a varactor based oscillator, while retaining ability
> to do audio rate frequency modulation?
> 

Ye Olde CD4046 I guess? Have you ever looked at how the oscillator in an EDP Wasp/Gnat works? The touch keyboard generates a digital clock that a 4046 PLL locks to, with the PLL generating the squarewave directly and its control voltage setting the ramp current for the sawtooth generator very much like a Juno DCO. The PWMed output is generated from the saw, as you'd expect.

I guess the audio rate modulation would be dependent on the loop time constant. The loop control voltage is lowpassed so that it doesn't become unstable. Think in terms of tuning a PID, you don't want it to respond too fast or it'll overshoot and you don't want it to respond too slow or it'll take forever to settle.

-- 
Gordonjcp