Jensen Copper Foil Paper-In-Oil Capacitor
Its reputation precedes it, and Jensen PIO capacitors are indeed excellent PIO capacitors. The word “musical” seems made for it, not by virtue of syrupy romance but by virtue of refined microdynamic texturing and tonality, which allows one to immerse in the music instead of analyzing it. If you are the type who can easily relax into music when it sounds “good” and be content, then the Jensens are perfect for you because they provide satisfying tonal color, harmonic richness, and smooth sophistication without becoming overly rolled-off, muddy, and slow. In fact, the upper-midrange to midrange has a lively character without brightness or dryness that is quite attractive indeed.
Compared to Russian K40y PIO, Jensen is simultaneously finer-grained yet smidge less dark, presenting music with seemingly more tonal purity and light. The Jensen difference is not huge, akin to a soufflé made with eggs beaten a little fluffier and lighter, but both taste like soufflé. On the other hand, K40y does come across a little more dynamic and denser in tone, so once again, we have choices.
So the oilers are great, but I am surrounded by mountains of capacitors from all around the world. Compared directly to some stupendous teflons, while not “overly” rolled-off or slow, Jensens *are* a wee bit less extended and slower, relatively speaking. The leading edges are perhaps not as sharp as a new razor, but it’s not far off. Bass definition also is not nose-to-nose with teflons or polystyrenes, but I think it’s good enough for me, especially for acoustic music. Jensens do serve up a tasty, warm, refined midrange, and if that’s one’s preference, one may even say Jensens are a better capacitor than teflons or other film caps.
-------------------------------------
FT-1 2200 pF Russian Teflon Capacitors (Bypass)

Jensens and other PIO’s are so good at what they do, it’s natural to feel the need to somehow improve them just a little where they are not state-of-the-art. I tried to accomplish this by bypassing Jensens with a small bypass Teflon capacitor, the FT-1 Russian capacitor at 2200 pF.
This does not completely change the sound, and the effects are subtle, but some may find them useful. The extreme treble does open up some, and triangles and chimes gain a little more definition. I don’t mean to imply the Jensens suddenly turn into Russian teflons, as they still sound mainly like Jensens. In my experience, better treble definition tends to lead to subjectively tighter bass signature, and the Jensens’ bass did firm up a trifle.
So have we created the perfect capacitor here? Not really. The original signature charm of Jensens does diminish by a measure, so if you loved Jensens for their billowing, grand, bloomy richness, perhaps you should leave them alone. If you are still curious, it’s always worth an experiment since these small Russian Teflon capacitors are quite cheap.