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K40 vs. Jupiter Copper vs. Duelund Cast PIO

Posted by banpuku on February 18, 2017 at 13:57:39:
Over the past year I have spent many hours with 3 caps all at the same value (0.47uF). To my ears in my system, here is how I perceive their sonic signatures:

1. Russian K40 have the most beautiful color and tonal richness. They add some real life like qualities to strings (violin, viola, cello). They are not as quiet as the Jupiters nor Duelunds, and therefore the K40s don't have quite as good a soundstage as the other 2 caps. Transients are a bit softer. All this said, I use them as bypass caps on my 2A3 cathode caps (here, I use the ClarityCap TC 65uF with a 0.47 Russian K40 to smooth things out).

2. The Jupiter Copper Foil caps have a very very neutral sound. No coloration that I can find. They tend to sound a bit dry (NOT etchy) and therefore need some richness to balance them out elsewhere in the amp. Good transients and dynamics, with a very nice black background. Deeper soundstage than the K40s, but once again, the K40s are king when it comes to tonal richness.

3. Duelund Cast PIO are used as my coupling caps between the ECC99 and 2A3 tubes. The Duelunds have the most quiet background and give a deeper soundstage. Duelund's have a neutral to somewhat soft tonal balance, but no extra richness like the K40s.

Since I listen to chamber music most of the time, I need the K40s somewhere in the chain to add some color, but the Duelunds are clearly the most natural sounding and thus, my choice for the highly influential coupling capacitor.

You can't go wrong with any of these caps. I have no experience with the Russian Teflon's but thought you might benefits with an evaluation of the others including the Russian K40s.