I have been a fan of Sennheiser headphones for years, having owned both HD 580s and HD 650s. I never had issues with them, and was baffled that some reviewers complained about a wooly mid-base hump, while others liked it, but I had never heard it. I finally plugged my HD 650s into a headphone jack that was woefully inadequate to drive them, and there it was! As both a musician and an engineer, that was an epiphany for me. Why did no one understand that the headphones were accurately reproducing the sound of headphone jack electronics crapping out? And why was no one pressing the issue that, in order to accurately reproduce music, the driver must be presented with an accurate copy of the voltage signal as it was mixed in the studio? There are many filters and transforms the signal needs to pass through between the mixing board and your ears, and crappy headphone jacks need not apply.
That’s when the crazy engineer in me took over. Long story short, I now have highly modified Muse Model 100 power amplifier with external dual mono power supplies, revised star grounding throughout. It has six extremely high quality MOSFETS per channel, with a highly respected and novel at the time feedback arrangement that provides dramatic dynamics with extremely natural and effortless timbres and soundstaging. The knock on this amp in its heyday was a bit of hum, but mine is now stone cold quiet and for headphones operating in pure class A. A switchbox allows me to switch between stereo speakers and my headphones. I also built a DYI cable using aftermarket Sennhieser connectors and a run of professional grade Mogami Neglex 2534 microphone cable to each driver. Microphone signals are the smallest, most fragile in the recording studio. These cables never had it this easy!
I loved my HD 650s on this rig but wished for better bass. Enter a new set of HD 660S2s. The first thing you notice is there are tons of “refurbished” open box samples available. All brand new, not even broken in yet. People are returning these things in droves. What is going on?
So the new cans arrive, I plug them into my Muse amplifier with the supplied cord and am completely gobsmacked! These things are dynamically compressed, with soundstaging homogenized and flattened so you can barely tell where anything is. Musical details are smeared together or lost completely. These things are junk! No wonder reviewers hate them and customers are returning them.
So I get out a cheap Cardas knockoff cable from Arctic Cables, and dynamics are better, soundstaging and details are better, but there is a familiar clanginess in the treble I recognize from playing with this cable before. By now the new cans are breaking in nicely and initial stuffiness is gone, so I pull my DYI cable from the HD 650s and start doing some comparisons.
Holy mackerel! When you mind their care and feeding, these new Sennhiesers are a revelation! The HD 660S2s are dramatically better than the HD 650s, and a bona fide audiophile reference. Dynamics, quickness, punch, rhythm and drive are incredible (also known characteristics of the Muse amplifier), and soundstaging and detail are stunning – almost like you are seeing all the sound sources with your eyes as well as your ears, and they never get congested no matter how loaded the mix. The overall quality that really blows you away is the smoothness. With so much dynamic punch you don’t expect world class suave delivery, but there it is. You are able to effortlessly follow many musical and lyrical lines at once. Top marks for both naturalness and musicality. You will not only tap your foot, but you will dance with the music and break out singing involuntarily! I am rediscovering my music collection. These headphones are the best purchase I have made in a long, long time.
If you are thinking of buying these headphones, but intend to use the stock cord… well, don’t bother. Save your money. But if you like music, grab yourself a pair, feed it from worthy electronics only, and get yourself a good aftermarket cord. Or make yourself one. It’s not difficult. You won’t be disappointed.