Hello mmakshak and DaveyF,
In regards to the DC Battery Power Supply on my Linn LP12 and what it does for the table and it's sound. It really does a number of things and I will try my best to describe my impressions, but please bare with me as I am probably not the best at putting my thoughts into words.
First of all, my DC supply will power the table at both 33 1/3 and 45 rpms by simply rotating a knob on the front of the power supply. Inside the power supply box are trim pots where you can dial in exactly the correct speed. This power supply does an excellent job of maintaining pitch stability. Their is not much that I hate worse than listening to a piano for instance holding a note and hearing the sound wavering about, or hearing an orchestra reach a huge climax and then listening to it's reverberations sound throughout the hall wavering on it's pitch. You won't find that happening with this supply.
Secondly, with the DC supply the music emerges from a totally black background. The best I can describe it is when listening to a really great performer in live concert. For example, I listened to Midori (famous violinist) play completely acousticly, with no amplification what so ever in our music hall. When she would start a phrase, the sound from her violin seemed as though it came out of a black hole, so to speak and it was soooo pure! This is what the DC power supply does. I believe that it eliminates the AC grunge that comes in on the line. The benefits of this come in the form of quietness, which allows for really great micro dynamics, a greater sense of dynamic shadings, which I believe goes a long way in communicating the musical message as it were. It also allows for startling, dynamic, transient attacks..... providing the rest of your system is up to the task, of course and the feeling of purity...both of tone and of whole.
Thirdly, because of the combination of excellent pitch stability, quiet black backgrounds giving the wonderful dynamic shadings.....the DC power supply provides the music with a great sense of movement. It doesn't sound as if it is racing or being forced, nor does it sound lagging. What it does sound like is natural as opposed to mechanical or electrical. It lets the music sound as if Midori is playing naturally in the hall, versus a reproduction of her playing in the hall. It sounds nimble and refined and effortless. Another example would be to compare a Conservatory of Music cello student to Yo Yo Ma ( I'm using Yo Yo Ma because virtually everyone has at least heard a recording of his or has seen a video of him performing as opposed to some of my favorite cellists who may be more obscure.) While the Conservatory student can have a nice tone and may be technically proficient enough to hit all the right notes and mostly be in tune, and therefore give an overall pleasing performance, it doesn't come naturally yet. When watching the student you can see the stress and tension in his face, in his body posture as he is fighting to force his fingering positions on the neck and trying to time that with his bowing technique. When you watch Yo Yo Ma perform, there is absolutely no tension in his body. He is fluid, nimble, and at ease. The cello and bow simply become an extension of himself and the music flows naturally and effortlessly.....nothing being forced or coerced as he is a Master of his instrument. This is hard for me to explain, because not everyone is blessed with being able to hear wonderful live acoustic music on a regular basis and unless you have been able to do that, I feel that you truly will not understand what it is that I am trying to communicate to you. What I can say though, is that once you hear your vinyl played on this DC system, you may no longer be able to tolerate hearing it on a system that differs.
The comments that I am making here are of course the opinions from listening to "my" DC power supply on my LP12. I will not presume that all DC power supplies will give you all of these benefits as there is so much more that goes into a power supply than just whether it is powered by AC or DC. Just as there may also be DC supplies out there that will surpass what I am using as well.
I am responding to your inquiries so late tonight because I was traveling today. I was able to stop in a very highend audio salon today and listen to an $8000 table, $3,000 arm, with a $7,000 cartridge. It was all very beautiful looking, however it lacked the naturalness, the effortlessness and liquidity of my DC powered LP12. Was this because the table that I heard was powered with AC or do to some other part of the audio system that it fronted? I do not know. What I do know is that this company's more expensive models use DC, so they must figure that there is some perceived benefit from it's use. More importantly, to the revelance of this thread.....the LP12 is very definitely still able to compete with and/or surpass todays current offerings from other designers.
In answer to the other question......No, I am not using the Keel upgrades..... I've never heard it yet in the flesh. I would be interested in hearing all of the various options that are now available for the LP12, but as I said in an earlier post.....I would listen though with an open mind leaving any preconceived notions checked at the door. Everyone has been blessed with their own individual set of ears and therefore one person may hear things differently than someone else. What appeals to one person may not be appreciated by another? So what is sometimes being offered up as an upgrade, may be considered by someone else as simply an option. I'm sorry that I cannot be of more help in regards to the Keel. However, may I suggest you look up Peter Swain from Cymbosis HiFi who has an exorbitant amount of both knowledge and experience with the LP12 and all of it incarnations, options/upgrades, and synergistic pairings. He is one heck of a gentleman too!
Sorry if I rambled on for too long. I hope though that it may be of some help.