It’s fair to say that the AF1 AF2 & AK share the same oscillators (DCOs) as each other but they all have differences elsewhere … the AK polishes the sound a bit whereas the AF2 has new filter/drive circuits
I will point to a thread with some thoughts on tailoring the original filter settings to make the source oscillators sound more open
With the benefit of hindsight (having now heard the AF2) I might add that the vanilla sound still sounds quite similar (in character) to me, but it’s evidently easier to refine it, so despite the filter overhaul, there’s a similar vanilla sound (i.e. it’s not that open/raw … it begs for a tweak)
In the thoughts discussed on the Mk1 below the impression was that the filter was the main reason why the sound took on this character - there’s also the fact that the default value settings for filter are not neutral (there’s e.g. a resonance bump) - adjusting the filter more can really change the character leading to the perception of a more open sound
Whether the filter is the only contributor (to this character) is not so clear … I suspect there’s just something about the source oscillators (especially defaults) which contributes to the impression
There is no doubt the AF1 can produce incredible sounds with, on occasion, too much bass (for my tastes) so it’s all there to be tweaked
Firing other synths through the AF makes you realise sometimes that the sweet spots of the other analogs are broader
Even compared to the AR (even before DVCO) you do get the impression that a simpler VCO oscillator can sound lovely with much less fiddling even through a broadly similar filter to the second AF one (not the ladder tweaked on Mk2)
The price you pay for the astonishing versatility of the AF designs is that you need to put in a bit more time tweaking - a good starter sound saved as your vanilla patch will help, I like the Triangle saved with 32 iirc ‘pulsewidth’ it sounds like a more juicy saw imho
Here’s the thread at the point of discussing filter tweaks and other aspects to do with oscillators - there are other aspects on this aspect of the AF, the bottom line is the sound is in there and it’s clear that the AF2 is a step forward (whilst retaining significant overlaps with the earlier models)