Sirdec

Well... no.
What I was saying was that clocks are not the problem here, they just give the power (pulsar, hopper-clock, ...) to whatever is making fps drops (dispenser and other stuff). It sure is about the toggling on/off of the redstone dust, but it is not about the clock itself (as the clock alone don't make fps drops).

At least this is what I think according to my tests.

You are right though, I made a mistake: I am not using droppers but dispensers.

Well, I did some tests on my world and the problem is coming from water flowing into another chunk (I am not saying for everyone). Also, just water doesn't cause fps drops, it has to be activated/deactivated by a dropper and it depents on how many water you have (I was able to get some short fps drops by gradually improve the surface of the plateform).
By the way, my clock is used to activate water flushing mobs (for a mob grinder).
I can share my tests here if needed.

Also I tried with just a pulsar (I think it's the name for the one I used), so without hopper and comparator, and I still get fps drops.

For me, it has nothing to do with clocks. Still, disabling them disable power in the circuit so it helps to temporarily fix the problem.
I will try with other stuff when I have time (Redstone lamp, Minecart, ...).

Same here, my redstone clock (hoppers) is within a single chunck. But I have redstone connected to it leading outside the chunck (on two other chuncks to be precise).

• My redstone system as it is causes fps drops on some chuncks

• If I have my clock active and cut the redstone going out of the chunck, I don't get any fps drop (I have droppers connected to this system inside and outside the chunck, so droppers inside the chunck are still working properly)

• If i let redstone connected to my clock into another chunck, fps drops are back

To me it seems like it could be related to some update it causes in another chunck.

Also the memory Minecraft uses isn't affected. And when those drop occurs, my processor usage is lower.