My tube preamp has a fully perforated top and appears to have nonshielded leads from rcas to circuit board. So why does covering the rca 's on back with Cardas Caps make a difference? It does make a difference. How can it?
I believe because what you're into a little yourself...
You get "pollution" into the circutry via the non-shielded RCA's, without the Cardas Caps. They reduce EMI and RFI.
I have them on all my XLR-inputs/outputs. I have though not tried testing with/without...
Since the wire isn't shielded inside the preamp why wouldn't it still pick up 10X the pollution with the perforated top cover being so open? Don't think pollution would only come in the RCAs.
Not saying they don't work. They seem to even in "open" top preamps. But why?
The Cardas RCA caps short the "hot" connector to ground on unused inputs, thus potentially reducing noise getting into the circuit.