I’d put money on them having fundamentally reworked the filter, clearly it has the same flexibility, but it has less of the side effects (especially with the filter at more open settings) … I’d say there is zero chance that the oscillator section is touched, it’s all about the filter … it now does what they’d have hoped for in the first model IMHO (i.e. the electrical design is finessed)
i’d imagine the sweet spots are simply easier to find which in itself is a huge thing, a good vanilla so to speak as you’ll be hearing more of the source oscillator goodness than before
i’d say the AK was a little tweak (possibly filter / possibly output side) whereas the newer A4 has a re-engineered filter (perhaps benefiting from the subsequent years of knowledge)
The AR filter is obviously simpler, but if it’s now sounding anything like that (AR does peachy mono sounds) with vanilla waveforms it’ll be amazing … I doubt we’ll be having this chat about the AR MK2, it already is untouchable on the sound side