The HD 540 Reference is the Sennheiser flagship of the mid-eighties. Those headphones have a sublime neutral sonic signature, with amazing mids, magical timbre and fantastic imaging. They can easily compete with today's Senns. But the pads and foam discs of my HD 540 were totally worn out and -- because of the almost inexistent sealing -- the bass was really weak. Last week, I ordered remplacement pads (the HD-250 Linear II pads fit perfectly) and original HD-540 Reference Gold inner foam discs still available at Thomann . And the result is... wow! Take for example a K240 -- well known for being neutral and smooth -- add 20% bass quantity and 30% bass quality (texture), a much-much wider 3D-like soundstage (HD 540 are fully open) with unmatched imaging, a lot of clarity, air and separation and a front row presentation, with intimate vocals. And l can't think of a more linear headphone. Hardcore neutrality. EDIT: "Luckily, I purchased the rare 600 ohms version. Needless to say: a juicy amp is mandatory. But the consensus seems to be that the 600 ohms version plays in another league than the 300 ohms version." At first listen, I wasn't impressed, nothing demonstrative (some would say thin, lifeless, cold...). But 3 minutes later, I understood why a guy on a german forum said the 540 are one of the best Sennheiser ever made. Such neutrality, clarity and smoothness are candy for the ears. It's like the HD 540 have no personality, they impose nothing but their linearity, which is the mark of a great headphone. Plus, they are a surprisingly good all-rounder. The KRK slogan "For educated ears" is kinda pretentious and arrogant but IMO it applies here... Musicality and realism, not dynamite. Once you get used to the HD 540, you will notice how amazing the timbre is. Vocals are transcendently good. Soundstage and imaging are fantastic. Comfort is unmatched, even better than the K240 since the pads are deeper and the HD 540 are sooo light. This post may sound like naive initial enthusiasm but I doubt it because -- when listening to Eric Burdon's "27 Forever" -- I suddenly realized how old those HPs are... yes, I bought them 27 years ago. I guess, I was too immature to really appreciate them at that time. Would a kid appreciate a rare Bordeaux? Anyone else loves their HD-540? BTW, 540 Reference and 540 Reference Gold are basically the same (the latter having hand-matched drivers though and cosmetic tweaks), but I'm not sure about the differences between the Reference and Reference II?