minecraft-java-editionminecraft-redstone
I am trying to replicate this design.
So far, I am making a copy of it, block to block, in my survival and creative worlds. They both lead to 1 result – all items are getting sent to 1 channel.
In his video I can see how first set of comparators flashes one by one, but in my case they seem to be off all the time;
There is no item actually called “Redstone Dust”; this is a colloquial name for the 
Redstone item, because it has the appearance of a pile or trail of powder. If this is what you have, then you already have the “dust” and you can use it as you have seen discussed.
If you have a stone-like block with red inclusions, then you have 
Redstone Ore. This is not usually the case because it requires an pickaxe enchanted with Silk Touch to obtain without breaking the block. To obtain Redstone from Redstone Ore, simply place the block and then break it with an iron or diamond pickaxe that does not have the Silk Touch enchantment. (You can increase the quantity obtained by breaking it with a Fortune enchanted pickaxe.)
This is the intended way of operation. As both hoppers try to push their first item each way, only one ends up moving.
To make hoppers pass the whole load before starting to pass it back, you need to block the next (opposing) hopper until your current one is empty. The standard way (that you mention yourself) is measuring the contents of the current hopper with a comparator, and feeding this signal into the next hopper.
Here's SethBling's hopper clock from Minecraftwiki:
Hoppers are directed clockwise, right now the items are moving from top left hopper to top right one, which is still locked by a signal from top comparator, and is already sending a lock signal to bottom right hopper.
For more designs, see this section on the wiki.
Best Answer
If the comparators are off that means there is no item in the droppers. You need to put a single item in one of the droppers to activate this circuit.