If you look at the schemactics for all of these instruments, you’ll see that they are all different. The 904 is different than the MiniMoog-- the Mini is different from the Micro/Multi, the Micro is different from the Prodigy/Rogue/MG-1, and again different from the Source/MemoryMoog… and finally different from the Voyager/MF101.
The MF101 is suppossed to be the same filter as the Voyager, and they seem to sound the same to me.
Although all Moog filters use a similar transistor “ladder” design-- each one uses different components and component values. Some are closer than others… but the Mini and 904 are probably the farthest removed from the others, using discrete transistors as oppossed to integrated circuits on all(?) the others.
I’ve had/heard alot of them (all except the 904, I think) and each filter sounds --somtimes slightly, sometimes distinctly-- different to me, aside from the groupings above, and below:
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Mini/ Sonic Six (totally different sounding synths, but the filters sound similar)
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Micro/Multi
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Prodigy/Rogue/MG-1
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Source/MemoryMoog
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Voyager/MF101
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Little Phatty
Also, as others have written, alot of the differences can be attributed to the oscillators and envelopes of the various instruments. But even so, I feel like each of the filters also have their own distinct characteristics.
The Micro filter has a weird responce where it only opens up at about mid-way on the dial-- which gives it a sort of “colder” sound (not neccesarily worse, just different) than the Mini’s extremely “warm”, if not “hot” sound.
The Rogue/MG-1/Prodigy filters have a very interesting, sort of band-pass quality that give them a very strong mid-range punch, but not as “fat” or bassy as a Mini.
The MF101 and Voyager have a much more “even”, and less idiosyncratic response–not the same “warmth” or “depth” as the Mini’s.
These are all just personal opinions and observations–and it seems like alot of people’s opinions vary quite a bit. So, you kind of have to listen to them all yourself to make your own opinions…
But to me, there is quite a bit of difference in each filter’s sound.