Shorted RCA plugs

[Andrew Pratt]

I went ahead and installed some RCA plugs that I'd shorted out on all the inputs on the back of my TA-E9000ES pre amp. According to This thread on the user forum its supposedly lowers the noise floor a little more. From the quick listening I did it wasn't a huge improvement but given the cost of the tweak (less then $10) I figured it wasn't hurting at all.

Any thoughts on this tweak Jon from an engineering perspective?

[JonMarsh]

In theory, this should lower the noise floor on unused inputs, (particularly if they're bipolar circuits) because of the lowering of the input impedance, which reduces the voltage noise and current noise. On FET input circuits, this will make a smaller difference, as the current noise contribution is very low regardless, and the intrinsic noise voltage of FETs doesn't reduce as much with reductions in input impedance.

An approach I prefer is Cardas Caps, which is a non-shorting billet brass, nickel plated cap which fits over the whole RCA input and shields against EMI and dust incursion. Unlike shorting caps, they can protect unused outputs, as well. I'm not really convinced about these yet, but they're inexpensive enough and look cool, so at the least they're a "harmless" cosmetic tweak. Others I know who's opinion I respect, with more experience with them (chief designer at Ayre Acoustics, for example), like, use, and recommend them.

You can get them from places like Welborne labs and DIYCABLE.COM.

If you try them, let us know what *you* think.

Best regards,

Jon




Earth First!
_______________________________
We'll screw up the other planets later....

[Andrew Pratt]

These sure look prettier then mine

http://www.diycable.com/cardas/rcac_shields.htm

I do have a few outputs that are open but I think for now I'll leave them as is.

[brucek]

Andrew,

I hope you're not considering using shorting plugs on any "outputs" of a preamp/processor as you stated. This is a low impedance output which is essentially a voltage source. It isn't designed to supply any significant amounts of current. It enjoys seeing the open unused circuit and won't pick up any noise.

I am a fan of shorting plugs on unused inputs though. Inputs are high impedance, usually in the order of 10K-50K and as such are susceptible to picking up some noise, RFI/EMI if left open.

I usually make my own shorting plugs from an RCA plug with any 10-100 ohm resistor. This presents an input load that will not allow any noise to enter. I would recommend this over a cap. What could the cap possibly do?
Do they really want us to believe that the RFI/EMI "only" enters through the small hole provided in the female RCA connector and that it somehow won't get to the "open" high impedance input of inputs left open through any other route? Kinda silly.... Do they feel that it won't be picked up by the wire that runs from the RCA connector to the input element because they capped the plug with some shiny metal? Mmmmm..

I would highly recommend loading all your unused inputs. A short or any small value resistance will do fine..

brucek

[Sonnie Parker]

I am very curious about the caps as well. I own the Sony TA-E9000ES. I've conversed with Doug about some shorted cables but decided it would be too costly. The caps idea looks good but I'm curious about what Bruce is saying.

I copied DIY Cable's comments/claims:

Cardas RCA Caps fit over unused female RCA connectors in your system to eliminate EMI and RF noise absorption.

Unlike traditional shorting plugs, these caps do not short the inputs (many pre amps do not like having their inputs shorted).

Another difference is Cardas RCA Caps completely cover the RCA input with a solid shield of nickel and brass to prevent both EMI and RFI from entering the chassis through the RCA dielectric.

This is a more elegant and probably more effective solution than either shorting plugs or wrapping the plug in aluminum foil. Our caps also protect the RCA from dust and corrosion.

Any takes on this.

Thanks!






SONNIE

Cedar Creek Cinema

DVD Collection

BFD Comprehensive Setup Guide

[Andrew Pratt]

No I just covered all the unused inputs not the outputs. How critical is the resistor vs just using shorted RCA plugs?

[Sonnie Parker]

Hey gentlemen/audiophiles,

How bout these:

They can be had for .69 each here:

http://shop.store.yahoo.com/triodeel/audandspeakc.html

These oughta do the job, right?






SONNIE

Cedar Creek Cinema

DVD Collection

BFD Comprehensive Setup Guide

[brucek]

Sonnie, they'll do the job just fine if you're on a budget. Radio Shack sell some inexpensive ones that might be a bit more attractive, but its difference would only be aesthetics. You can solder a small value resistor or wire across the plug and you're set.
Remember, you're only concerned about analog inputs - not digital inputs. Digital inputs do not have this noise floor concern. The levels of RFI/EMI would not be strong enough to be considered.

Andrew, I think it's really only important to draw down the inputs to some reasonable level of resistance, from zero to 100 ohms. It would be equally effective no matter what value in this range that you choose. I can't imagine what Cardas is referring to when they express concern about some preamps not liking this procedure? Most sources outputs that will be connected to these inputs will be in the order of 10 ohms to 100 ohms output impedance. If you're concerned, then simulate this and use that value of resistor - but it really isn't necessary.

I don't really want to put down Cardas, but again the notion that capping your input connectors as being the only path to get to the high input impedance line stage is silly. RF can easily pass through your case vents and be detected on the short signal path from the capped connector to the input element. It's acts a bit like an antenna when left open at its 10K - 50K input impedance. Drawing the input down to ground will alleviate this problem. It's actually a very, very minor problem, but every little inch helps..

brucek

[Andrew Pratt]

thanks bruce...got any more cheap tweaks up your sleave?

[Sonnie Parker]

You can solder a small value resistor or wire across the plug and you're set.

bruce, just to be sure (I'm not resistor/resistence friendly - working on it though), I won't need to do this soldering if I use the el cheapo's. The plug is already shorted. I would only do this with the Ratshack plugs, right?

Thanks






SONNIE

Cedar Creek Cinema

DVD Collection

BFD Comprehensive Setup Guide

[brucek]

Sonnie,
Yeah, if it's already shorted, it's good, but it doesn't look shorted to me. I think it says on the web site you gave, "for shorting plugs"...

Andrew, well, as you probably know I play on the engineers side of the street and that's a dirty word over here ...

brucek

[Sonnie Parker]

If it's shorted it would be one solid metal piece with the center pen shorted to the outer shield and the metal acting as the resistor, right?

I believe this is one solid piece, but if it were not, where and what resistor would I need?

Thanks,






SONNIE

Cedar Creek Cinema

DVD Collection

BFD Comprehensive Setup Guide

[brucek]

Yep,if it's one solid piece, then it's a shorting plug - it was hard to see from the diagram. The short is a zero ohm resistance....
Normally, when you buy a RCA type connector it has a separate center pin insulated from the shell. To make your own shorting type plug, simply short these two together by soldering a wire or puchase a small resistor at Radio Shack if you wish and solder one end to the pin and the other to the shell. You can use any small value - buy a pack of 1/4 watt 75 ohm resistors and use them - they'll be fine...

brucek

[Sonnie Parker]

Thanks bruce,






SONNIE

Cedar Creek Cinema

DVD Collection

BFD Comprehensive Setup Guide

[Andrew Pratt]

Sonnie I grabbed a packet of RCA's that had a removeable plastic cap over the metal RCA's. they came in a pack of 8 for under $5 each to so cost was minimal. Solder was easy to since the centre connector can bent easily over to touch the side wall where all you need is to tack the two together is solder and put the plastic cover back on. IMO they look clean and work like a charm.

Bruce I'm all for science based tweaks !!! (I've got a B.SC in Biology so I come from a science background)

[David Meek]

Jeez guys, quit making me spend money.

I couldn't help myself. . . I really couldn't! Those Cardas caps are so nice looking, I bought a dozen. Actually, my Yammie RX-V1 has a known issue that these will solve above and beyond a lower noise floor. When the 6-channel inputs collect enough dust (and it doesn't take much) they'll shut off the amp for that channel or channels. Quite disconcerting, and it's hell to try to diagnose if you aren't aware of it! The caps'll save me having to clean these inputs on a regular basis.

Thanks for the link Andrew.




David - HTGuide flunky
Our "Theater"
Our DVDs on DVD Tracker

[Andrew Pratt]

glad I could help