this is a modified version of the standard upwards DBE(double block extender) made to work downwards

this is the 1 wide single DBE in the 'closed' state (right-click or run a redstone wire over the noteblock)

this design is tile-able

remember to make the observer on the right most piston match the state the dbe is in so that the extensions and retractions actually works

same thing but 'open', you can see the observer on the right of the image is flipping from top to bottom in the images and that is to allow the last pulse needed to run retract the last block

this is the stacked dbe, below is how it works and how to make it

this is a double dbe which is similar but a little modified, this is the 'open' state

'closed' state

below is a sliced version of this extender for a tutorial like purpose

this is the front 6 blocks, the input is wired into this redstone,you could even use noteblocks with redstone over them, or you could use powered rails too.

this is basically just two dbe side to side mirrored, remember to make the observer on the right most piston match the state the dbe is in so that the extensions and retractions actually works

as putting two of the dbe next to each other takes away space for the extra wiring, this little thing has to fill in