I have 90 of them installed. Couldn't hear any difference but I could swear my VCR's picture was less grainy after installing on the unused inputs. Testing with them on and off did produce a difference that only I could see. In other words, they probably do close to nothing. However, they look good (especially on front inputs) and they protect the RCA connector itself. Knowing what I know now I probably would have gotten plastic covers for protection only but I'm not dissappointed with the Cardas caps. Sean's idea is probably the way to go but I've heard many preamps don't like shorted inputs (I have no personal experience with that).
Do "Cardas Caps" make a difference?
A new inexpensive, and quite compelling, tweek are the caps George Cardas makes to cover unused input and output jacks, therefore rejecting stray EMF. This is a logical tweek, and I trust George's integrity here, but my question is: How noticeable is the improvement? Can everyone who has tried them hear a difference?