I've got them, and well...... they keep the unused inputs/outputs clean :)
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You can experiment with some Aluminum foil, a scissors, and a bit of Scotch brand transparent tape.
Cut the foil into 1/2 inch wide, 2 inch long strips, roll it up around an unused RCA jack, tape it (small rubber bands also work well) and flatten the end up to seal out those evil stray electromagnetic waves. Repeat on all unused RCA ends.
The caps were made to COPY things some folks did... with guess what??? Aluminum foil strips!
Nearly free test. If it seems to do somthing for you... buy the Cardas... if not, forgeddaboudit.
How about combining Elizabeth's idea with that of Dave's or Hepl's ? Put a tiny square of aluminum foil up against the backside of the female RCA and slowly push the plastic cap over the jack. This will "form-fit" the foil and no need for tape. Much easier to work with at minimal expense. Thanks !!!
El: I've recommended using shunts on unused inputs for a LONG time. While direct shorts are normally good, many components that lack the proper isolation between inputs respond poorly to this trick. In such a situation, one should solder a low value resistor ( 50 - 500 ohms ) across a cheap RCA plug and use it. This simulates the typical load that most inputs would normally have on them and keeps the jacks from getting pitted at the same time. Phono inputs should use a very high value resistor i.e. many, many Kohms. Sean
El: Due to variances in circuit design, especially with a high gain circuit like a phono stage, it is possible for a preamp to go into oscillation with a dead short at the input. Resistive shunts basically close the circuit and any "foreign signals" are resistively absorbed via the impedance of the resistor used for the shunt without loading down any other circuitry that may be connected through poor design / crosstalk. Then again, i know i'm preaching to the choir when talking to you about stuff like this. Others may not know how stuff like this works, hence the explanation.
Ross: I don't think i want to know what you were planning to do with the aluminum foil, but thanks for making mention of this anyhow. It made me think about the foil touching both the female and male part of the RCA, which would act as a shunt or short circuit rather than just a shield. While this might be okay for most inputs, it would definitely be a BIG "no-no" for any unused outputs. As such, one should check to see if their female RCA jacks as mounted on the chassis of a component have the center conductor recessed or if they are flush with the outer section. If they are recessed, this is not a big deal. If they are about even with the ground terminal, be careful if trying to make "Elizabeth shields" out of foil : ) Sean