RCA Shielding Caps

Doublej · « **on:** 23 Dec 2012, 12:34 pm »

Does putting RCA covers on unused inputs and outputs help? Does the material make a difference? On Ebay they have soft plastic, hard plastic, gold plated or rhodium plated copper ones.

Anyone has a cheap source for these?

Elizabeth · « **Reply #1 on:** 23 Dec 2012, 01:14 pm »

I bought a hundred plus from a Taiwanese seller on eBay last year. (Vintage_audio_lab)Anyway, for me, yes they improved the noise floor slightly.
The most noticable was on my 42" Plasma TV. (i covered the unused RCA vidio and sound)
The ones I bought were gold plated metal. 20 for $15
The improvement was minor, but it was an improvement.
(now there is also a US seller with the same caps.. search RCA caps on eBay)

Speedskater · « **Reply #2 on:** 23 Dec 2012, 01:47 pm »

The only difference is decorative.

usp1 · « **Reply #3 on:** 23 Dec 2012, 03:46 pm »

I read that one should use shorting plugs for rca inputs and non-shorting caps for the outputs.

WireNut · « **Reply #4 on:** 23 Dec 2012, 04:02 pm »

I use 8 of these on the unused inputs of my preamp.
http://www.takefiveaudio.com/mall/shopcontent.asp?type=RCA_Input_shorting_plugs

Letitroll98 · « **Reply #5 on:** 23 Dec 2012, 04:13 pm »

Quote from: usp1 on 23 Dec 2012, 03:46 pm

I read that one should use shorting plugs for rca inputs and non-shorting caps for the outputs.

Yes, that's correct. Shorting plugs on inputs actively reduce the noise floor on all components. VERY IMPORTANT, do NOT use shorting plugs on outputs. I leave my outputs uncovered, but you can cover them with blank caps if you like the look, it won't do anything to reduce noise, it may help prevent oxidation, I don't know.

VERY IMPORTANT, you must use real shorting plugs to make any difference. I make my own out of cheap RCA plugs, soldering the two legs takes about 30 seconds and they cost pennies each, but you can buy them on eBay, but they MUST have the positive pin to actually short the input, like these: http://www.ebay.com/itm/4-Pcs-BRASS-GOLD-PLATED-Audiophile-RCA-SHIELDING-CAPS-/251192305595?pt=US_Audio_Cables_Adapters&hash=item3a7c3a67bb

Note you can also remove the positive pin to make these blanks for output use. The Cardas plugs with no center pin are not shorting plugs.

If you use real shorting plugs on all unused inputs, it has to be all, even one uncovered ruins everything, the effect is not subtle, its rather dramatic. It makes you equipment sound like you spent way more than you did.

Folsom · « **Reply #6 on:** 23 Dec 2012, 05:25 pm »

Quote from: Speedskater on 23 Dec 2012, 01:47 pm

The only difference is decorative.

Actually I am thinking it might be possible to increase noise by making a bigger antenna, with them. You could also be reducing the RF pickup by lowering the potential for RF between the positive and negative on the RCA jacks but... if any of this makes a difference I don't know. I'll test it out if someone sends me some freebies.

Really it is probably just providing more ground reference. This could also be achieved by attaching a large piece of copper or wire to the negative terminals of the RCA inside the amplifier. That may not actually be a bad idea since it doesn't un-isolate the RCA jacks, and it works for speakers (expensive little tails that attach to the negative terminal sold by some company I forget who).

WireNut · « **Reply #7 on:** 23 Dec 2012, 10:07 pm »

I use 8 of these with great success.

Neutrik 352G RCA plug, 470 ohm resistor 1/4 watt.
Parts at Mouser.com
Cost $1.50 per plug ( even cheaper with plastic plugs )

Doublej · « **Reply #8 on:** 23 Dec 2012, 11:48 pm »

So what's better, a short or 470 ohms? Why is 470 ohms the magic resistance?

Folsom · « **Reply #9 on:** 25 Dec 2012, 07:16 am »

Resistance might provide RF rejection. That might be a good way to force RF towards earth ground (chassis) instead of signal connections which are isolated.

However this would only work for RF trying to collect on the positive areas that are cut off. It would only work if RF likes to enter at the very utmost end of something. If RF does work that way, end-caps alone would move the RF receptive "ends" to the inside of the box.

Peter_S · « **Reply #10 on:** 28 Dec 2012, 05:47 am »

What about preamps with both balanced and unbalanced inputs. Is there anything that must be done to the balanced inputs to acheive the benefit?

Elizabeth · « **Reply #11 on:** 28 Dec 2012, 07:15 am »

Quote from: Peter_S on 28 Dec 2012, 05:47 am

What about preamps with both balanced and unbalanced inputs. Is there anything that must be done to the balanced inputs to acheive the benefit?

Cardas and others also make caps for the XLR in and outs.

harley52 · « **Reply #12 on:** 30 Dec 2012, 04:16 am »

Gee, and here I thought the OP was asking about simple caps for the RCA's on his equiptment. Keep it simple.

Elizabeth · « **Reply #13 on:** 30 Dec 2012, 04:34 am »

Quote from: harley52 on 30 Dec 2012, 04:16 am

Gee, and here I thought the OP was asking about simple caps for the RCA's on his equiptment. Keep it simple.

Hah hah hah "Keep it simple".
Some folks just have to explain it all. Plus more.
Leaving any angle unexplained makes some members feel they have not done enough.
Generally that is not so bad for posterity, and all the future folks reading stuff. Though it usually leaves the op of the post mystified and having even MORE questions.
THus I would tell the op forget the resistors thing. too complicated.
And if the OP DOES go for the shorting plugs. THEY ARE DANGEROUS! When you short out the outputs by mistake.. ((Most likely? the tape out) You will be sorry. (I who an a quasi expert would NOT use shorting plugs AT ALL due to the stupid mistake possible of shorting out the WRONG jacks.) K.I.S.S.

harley52 · « **Reply #14 on:** 30 Dec 2012, 04:41 am »

Are you the same Elizabeth as the one on A-gon? Just curious.

stevenkelby · « **Reply #15 on:** 30 Dec 2012, 04:43 am »

Why is 470 ohms the magic resistance?

WireNut · « **Reply #16 on:** 30 Dec 2012, 05:09 am »

Wish I could answer that question.I got the recipe from TakeFiveAudio.
I bought the components, built the DIY project, and Lo and Be-hold they work great.
I've done the dead short before, but I like the 470 resistor better.

I think it has something to do with presenting a load to the preamp instead of a dead short.
I will continue to use them.

Possibly 10 times the average input of a typical preamp. YMMV.

Steve

Doublej · « **Reply #17 on:** 31 Dec 2012, 08:07 pm »

I appreciate everyone's input on this topic. Here's a Stereophile article to a different use (?) of an RCA shorting cap.

http://www.stereophile.com/finetunes/212/index.html

Speedskater · « **Reply #18 on:** 31 Dec 2012, 11:23 pm »

That Jonathan Scull article on noise tracking is excellent, but I'm not sure that Radio Shack still stocks equivalent parts.

But the shorting plug is for the selected input, so that you only test for noise past the input.

All the other non-selected inputs that don't have noise antennas (some call these antennas, interconnect cables) will not contribute to noise in your components.

Elizabeth · « **Reply #19 on:** 31 Dec 2012, 11:35 pm »

Quote from: harley52 on 30 Dec 2012, 04:41 am

Are you the same Elizabeth as the one on A-gon? Just curious.

Yes i am the same Elizabeth on Audiogon and Audio Asylum.
Can't you tell??? LOL