The Marco-boy main system, as of August 2020

[Barry]

I'm not disputing the physical differences, only the terminology. Your link is for the Pro 4AA.

My Koss Pro 4AAs are most certainly original (they have a 'khaki geen colour and made in the US by Koss; I didn't know that 'replicas' were being made elsewhere. They must be illegitimate copies, as I can't understand why Koss would continue production of the 4AAs after introducing their replacement: the Pro 4AAAs.

If your Pro 4AAs are a copy, then it is possible the SQ is different (and inferior) to the original Koss design.


But all this is by the by: as I have said elsewhere, I'm not that keen on listening with headphones, but pleased you are pleased with your new 'phones.