Ques Re: Use of plugs/caps on unused jacks - diyAudio
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Old 7th May 2009, 03:01 AM   #1
clm811 is offline clm811  United States
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Default Ques Re: Use of plugs/caps on unused jacks

What is everyone else using on their unused input jacks?

I'm currently using a high quality AV preamp in my system, and want to minimize noise pickup/radiation from the unused input/output jacks(all unbalanced)RCA-type).

I have Cardas caps, as well as a variety of RCA plugs with either 75ohm resistors or shorting wires across the center-
pin to collar.

I understand that some preamps like shorting plugs on the (unused)inputs, and some don't.

Thanks in advance!

-Chas
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Old 8th May 2009, 06:44 AM   #2
clm811 is offline clm811  United States
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Let me re-phrase my questions:

1. Does anyone know of any reason NOT to use shorting plugs on unused line-level inputs?

2. Would resistively-loaded RCA plugs be better than plain metal caps on unused preamp/processor outputs? My interconnect cables are properly shielded, as is the pre-pro chassis, against radio frequency interference.

I have some plugs containing 75ohm resistors, for unused video and digital outputs.

I'm in a fairly RF-noisy environment & seek to reduce RFI pickup.

Thanks in advance.

-Chas
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Old 13th May 2009, 01:50 PM   #3
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Read this topic here http://www.audioannex.com/printthrea...62&type=thread

It will answer your questions it seems.
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Old 13th May 2009, 07:17 PM   #4
clm811 is offline clm811  United States
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Default The best explanation yet

Exerpted from post at the above link :
Quote:
RFI/EMI are the two problems that Cardas caps, or shorting plugs might influence....
The highest gain inputs are where you're most likely to hear a benefit, all else being equal. If stray RFI gets into an unused phono input, it will be amplified by the gain of the stage, imposing itself on the power supply rails (and so into other stages), can easily bridge the internal gaps in selector switches (and so get into other stages) and might even drive a stage into oscillation. The grounding design and implementation in your amp will also affect how big an issue this is...
...For lowest noise, I would use a short[ing plug], otherwise you're just adding the Johnson noise of the resistor into the circuit too. However, some pre's have line selectors and tape loops that might not work properly if one or more of the inputs are shorted, or it might make some odd thumps as you select a different input and the switch moves past the shorted one. If either of these things are an issue, try a 10K resistor, or remove the shorting plug.
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Thanks!

-Chas
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