New member here, thought I would share my experience assembling a set of DIY balanced cables for my HD650s.
Like so many others I had been seduced by the listenability and comfort of these headphones, their balance and musicality that just seems to improve over time (or more likely, my ears tune out the shortcomings). But - the infamous, much-commented-upon veil...which is real, caused I'm guessing by a drop in energy in the presence band compared to other headphones (many of which deliberately exaggerate this region). Could new cables run in balanced mode improve matters?
At the suggestion of the designer I'm driving the HD650s directly from the output of a Wyred4Sound DAC-2 which is also connected to my regular amplifier which drives my speakers. This DAC has plenty of juice, enough to drive much less efficient headphones than the Sennheisers. And it has true balanced outputs available, perfect since I run single-ended into the amp.
I ordered a set of the two-pin connectors labelled "Acrotec" from a Hong Kong vendor on eBay. I believe Kimber also sells them. They fit the headphone inputs perfectly and are color-coded left and right.
Then I ordered two 20 ft. cables made from Mogami 2549 (their low capacitance mike cable) terminated at one end with Neutrik NC-FXX XLR plugs and at the other with tinned bare wire ends. These came from NY Pro Audio Cables and I cannot recommend them highly enough - the cables arrived very quickly and workmanship was outstanding (no affiliation here either). Cost was $60 for the pair, plus $14 for the Acrotec plugs. Then I soldered the tinned ends of the cables to the plugs (a little tricky; they're small). Now I have two cables - one per channel - with two balanced conductors each and a shield connected at the source end. The only drawback - and it is slight - is that the new cables are thicker and less flexible than the stock Sennheiser cable. Nothing I can't live with, though - in fact, I like that they don't try to curl around my chin like the stock cables do.
And the sound? In a nutshell - my HD650s are transformed. Bass goes deeper, transparency is hugely improved while retaining the headphones' signature musicality, I can simply hear much deeper into the mix and pick up details I never noticed before on familiar recordings. I'm not a cable obsessive (which is one reason why I chose the DIY route) but I have to admit this project really surprised me. Whether I am hearing the improvements wrought by balanced mode, better cabling, or both I have no idea, but for $74 how can you go wrong?