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Virtus-01 with Electro-Harmonix.
I have to admit that it took me some time to find a proper key for this headphone amplifier. At first I listened to it with the AMG Viella12 turntable and Manley Chinook phono stage. There I found the sound a bit too bright and thin. But except for proper tonal balance everything else I expect from a high-end headphone amplifier was there: great resolution, great spacing—relative to headfi staging of course—and amazing dynamics on the macro scale above all else.

While some tonal balance modifications were clearly audible to influence the sound of this amplifier, when I changed the source for an Ancient Audio Lektor Air V-edition CD Player and put the White Bird on Acoustic Revive’s TB38 platform—a smaller version of the RST-38 dedicated to power distributors and small amplifiers—I was finally presented with what I expected from the very beginning: pure music.

Now the Virtus-01 delivered a very mature sound and it sounded somehow similar with every headphone I used. While with each pair some characteristic features of their sound were audible, this amplifier did not emphasize them. It didn't choose either/or. I would explore the Virtus-01 with the HifiMan HE-500, Beyerdynamic DT990 Pro (vintage) and Sennheiser HD800. If I had to narrow it down even more I would focus on the HifiMan and Beyer which proves how capable this amplifier is. The planar magnetic headphones are quite difficult to drive and the high-impedance DT990 also don't work well with all amps. With the ultra-difficult HE-6 it wasn't bad either. Here I admittedly had to crank the volume to the max but encountered no distortion or compression to say a lot about power supply stability and output tube capabilities.

But in the end I was left with two pairs of headphones – HE-500 and DT990 Pro. The latter’s vintage designation is mine, not the manufacturer's. I use it to emphasize that my pair was made a long time ago and might not be identical to the same high-impedance model which is still manufactured today. These are one of the most interesting headphones which have been available for many years.

Back in the day these were one of the best and used in many studios along with the closed-back DT770 Pro version. While since then many other great headphones have appeared from AKG, Sennheiser and also Beyerdynamic—their T1 and T5p amongst those—it seems that the DT-990 Pro still has a lot to offer. I first took them out from a drawer after a long hiatus whilst reviewing the Funk Tonstudiotechnik LAP-2.V3 where they performed amazingly well. But years in a drawer had made their marks on the pads and covers.

That's one thing we usually don't discuss in reviews because it's not possible unless one simply holds on to something for far longer – how manufacturers support their customers. Beyerdynamic obviously takes really good care. I contacted the Polish distributor, paid for my order and 2 days later had the new covers, ear pads and headband padding. That's customer care!