It's very difficult to describe its quality with words and almost impossible to do without comparing with other decks, so I'll do.
Until now I was using my beloved Super-D6C (a specially modified and upgraded SONY D6C by Dr Walkman in Italy), a very good recording made with in on a SONY UX-Pro and a Sennheiser HD280 Pro professional monitoring headphone.
But since 2012 I had put big interest in learning more about audio quality and trying to find out what's the world's audio best quality out there.
Many new and extraordinary decks were incorporated to my collection, like a highly upgraded Pioneer CT-F1250, a Nakamichi RX-505, a Revox B215, a Tandberg 3014 or a highly modified Technics RS-B965, so I think I can say I really know good a tape can sound.
I also acquired some extraordinary headphones, like the Sennheiser HD650, the famous HD800 and the legendary SONY MDR-CD3000, which are far better than the 280 Pro.
I also highly improved my listening skills. I can now detect distortions or issues when I heard nothing 4 years ago. However, there's still a lot to learn for me and, while I can say I'm prepared for a subjective evaluation, there are people out there much better than me for doing such a evaluation.
I had the chance to hear by myself an extraordinary stack oof high-end gear and even to listen to a 200,000 € gear in an acoustically conditioned room, so I guess I could learn that.
For the testing, I've connected my TEAC V-8030S and my Nakamichi RX-505 and let all them run for more than half an hour (to warm up). aAs I have all them connected to a simple audio switch (no circuit inside) so I can instantaneously switch from one to another.
I recorded two identical Maxell XL-IIs from '88 exactly the same way, using a deeply cleaned vinyl disc. Of course, I recorded the very same songs, that I carefully chose for having an extraordinary recording quality and for being excellent samples for testing.
- Thriller by Michael Jackson (original USA pressing, mint)
- Sledgehammer by Peter Gabriel (original UK pressing, mint), and
- I Can't stand the rain by Tina Turner (original USA pressing, mint)
All were deeply cleaned and played in my Technics SL1200 LTD with an Audio Technica AT-440MLa and my ANT-Audio Kora3T Limited Edition high-end phono preamp and recorded in my upgraded Nakamichi RX-505.
For listening I've used both my Sennheiser HD650 and HD540 Gold Reference high-end headphones. I stopped using my HD280 Pro for testing as I realized they are not as good and have almost no soundstage.
The Sennheiser 650 is a big one, a bit old but still considered one of the best headphones ever made. And it has a huge number of fans, (including me). However it has much higher impedance and it can only be fully enjoyed when using very high quality headphone amplifier, like my ALO The PanAm.
When you compare decks with such a superb performance, differences become very small and usually are entirely up to the listener's taste. I have done both objective and subjective testing, and I'll try to comment on both sides.
Compared to a walkman, the K909ES beats them all. Period. No walkman can achieve the clarity and sharpness of it, specially after being upgraded by Alex. If I compare it to a good mid-level walkman, like a SONY WM-504 or a WM-B39, it is at a far higher level, but if I compare it to some of the best ones, like my Super-D6C, my Super DC2 or the Superb DD9, then the difference is not big. Not very small, though, but not big indeed. The walkmans have a narrower sound, and sound a bit muddy compared to the K909ES.
I've compared the K909ES to my TEAC V-8030S and to my Nakamichi RX-505. In regards to the TEAC, the playback is almost identical. The TEAC seems to be more sensitive to azimuth issues and sometimes it sounds a bit narrower than the K909ES. But sometimes it sounds a slightly bit wider. The overall frequency response is the same is almost every aspect.
Compared to my RX-505, it clearly stands behind. The Nak records and plays with a wider sound
which is very clearly noticed. The response is very flat in both, being the Nak maybe a bit brighter with some tapes but more or less the same. So the K909ES stands amongst the very best, being in front of some but behind of others like this RX-505.
To analyze the sound I've tested the deck with 7 different cassettes, going from a standard type I ferric to a high quality type IV metal tape, through some popular and excellent chrome
type II tapes:
The 7 tested tapes. From top to bottom and left to right:
BASF Chrome SuperII, SONY HF, TDK SA, TDK AR Limited Edition, SONY UX-S, SONY UX-Pro and MetalXR.