I debated on weather to post this here or in the LAB since it's a review of a DIY type component/mod. Obviously the Critic's Circle won...
I installed a pair of Jensen copper foil in oil coupling caps in my preamp (Transcendent Grounded Grid) this week and have been amazed at the presentation. By presentation I mean how the music is presented rather than specific portions of the audio spectrum.
First and foremost the system sounds more like a musical event than a reproduction. The music seems freer and less tied to the speakers. The speakers (Vandersteen 3A sigs) already did the disappearing act very well and imaging in my living room is spacious and deep. The addition of the Jensen's enhanced this effect and brought out the subtle spacial queues that help transport the listener to the performance. This is especially true on live performances. However, even studio recordings seem less like a recording and more like live music. It obviously doesn't sound like a real performance (no system I have ever heard does) but it's certainly closer than before.
As for specific sonic areas; the bass is deep and tight, I had to turn my subs down a bit; the midrange, particularly vocals, is very smooth but with plenty of bite if the music contains it. Listening to the Ray Brown Trio, Summer Wind this evening I was struck by the clarity of the piano. Both the sound of the hammers hitting the strings and by the complex harmonics and resonance of the instrument. One area which I am not completely happy with is the higher frequencies. Reproduction of cymbals seems slightly fuzzy. Not bad but not as clean as other coupling caps I have tried. This may be a break-in issue as I'm sure it will take some time for them to fully form. I did break them in on the bench for a week but at a fairly low voltage compared to what they see in the preamp.
Even with the slight reservation on the very top frequencies the overall sound is, IMO, very good. The kind where you just think, "damn this sounds good" while listening to music.
While these caps are not inexpensive ($24.60 ea for 1uF/630V) they are certainly cheaper than the majority of cables and many other tweaks out there. I approached this mod with a jaded attitude as I have tried Auricaps, Axon, Solen and some inexpensive Xicon metalized film/polypropylene caps in this preamp and found the cheap Xicon's to provide the best sound. I put off buying the Jensen caps for months because of less than good results with the aforementioned caps. Now that they are in the system I am delighted with them, especially if the top end improves a bit.
If you have a tube preamp and don't mind getting out the soldering iron, these are certainly worth a try. IMO, there are not many things for $50 that you can add to your system that will provide the improvement I saw with the Jensen's. One caveat is the size, these are large capacitors, about the size of a D-Cell battery.
Transcendent Grounded Grid. The GG has a DACT attenuator, HEXFRED's, bypass caps on the audio board, damping mods, NOS Mullard's wearing Herbies Halo's and of course the Jensen's. The feedback has also been reduced by about 3dB.
Philips SACD 1000 with much damping compound, BG caps, LC Audio ZapFilter output stage.
DIY low capacitance shielded cables terminated with Bullet Plugs
Odyssey Xtreme Mono's (the only things without mods - for now...)
Music Hall MMF-5 with added damping to upper plinth, Mogami cables, Grado Statement Platinum, Herbies "Way Excellent Turntable Mat"
Hagerman Cornet built as the "premium" version.
Vandersteen 3A signature's and 2 Vandersteen 2Wq subs.
Amps fed by BPT 2.5 Ultra, all other gear fed by BPT BP-4, each piece has it's own circuit. The BPT's are plugged into an Acme silver plated, cryo treated outlet. Power cords from the BPT's to the gear are all DIY based on the Bob Crump recipe.