HD 650 has been my very first purchase of a high end headphone. At the moment i received them i plugged them into my essence ST. At first i was extremely disappointed. I decided I would give them some burn in time and see what it does the sound. I later returned and I felt i could hear a very slight improvement but I still wasn't satisfied with it.
So I went online and ordered the m-stage along with the class a modded opa627. I waited a few days for the amp to arrive and I tried plugging the HD 650 directly into my Zen X-fi instead of my ST. And guess what, there was barely any difference; the only difference was the changed FR of the source (the zen vs st).
Anyway, the M-stage arrived. At first my jaw dropped at emphasized dynamics. The bass got tighter and the highs were brought out. However, after a few hours i realised that it was just that, a wow-effect. When i started to listen in a relaxed and focused state things started to fall. The bass was now tight, but it had lost all character and weight. The highs plus the very dynamic sounding character of the m-stage made the HD 650 into a kind of headphone I dont believe it is supposed to be, going from its "ground signature". By ground signature i mean the sound signature when I listen to the HD 650 and subtract any coloration or altering from the source and/or amp, where I get the hint of source/amp from using other headphones.
Or in other words, to me it sounded like the M-stage was pushing the HD 650 more into a brighter sound. And the result was that the mids suffered badly and the warmth and smooth character of the HD 650 had disappeared, leaving it in a more crippled state. Despite the highs and everything, it sounded somewhat veiled because of the inferior midrange.
This lead me into making a thread on this site where i posted some various observation listening to my gear. And i was suggested to get a tube amp, which i did.
And I can now 100% confidently say this. Get a tube amp, or get another headphone. Compared to all the other SS options, this is in a completely different class. The warmth can now be heared in a sort of natural/realistic state instead of the "fake" warmth the HD 650 sounded like before. The highs are still very present, yet very relaxed and doesn't sound as "digital". And the bass keeps its weight as when i had it connected into the ST, but it sounds a lot like more the bass "integrates" into the midrange. It just sounds so smooth, as if all the different frequency ranges was weaved into each other. Listening to music from the amp feels like sitting behind a very tinny piece of glass, where on the other side all the music is in its purest form. I will never be plugging my HD 650 into any SS amp again. Unveiling/amping the HD 650 is not about bringing the bass down and the highs up, it is about giving them enough midrange love and it will sound very clear, smooth and most of all complete.
The tube amp i got is the Argon HA2. It is only distributed in scandinivia and it has been very newly released so there isnt much information about it on the internet at all. I had a chance to listen to it in my local hifi store. Having also listened to a X-can V8.P, I believe they are very close in sound signature.
Anyway, you should really try a tube amp with these, especially if you get disappointed at first listen.
