Phono shorting plugs, what's the deal?

[Bigears]

Some of my vintage gear came with the original phono shorting plugs and some did not. My Yamaha CR2040 for example doesn't have these plugs and I don't think came with them new. My Sansui's did on one of the phono inputs but not the other. What are these supposed do?

What is the purpose of these plugs and do I need them if I never use the phono input?

TIA.

 

[RichPA]

By shorting the input, you reduce noise pickup for that input. They are most useful on phono inputs because of the high gain on that input. If you have noise problems, they're worth a try - if not, don't worry about it.

 

[Bigears]

By shorting the input, you reduce noise pickup for that input. They are most useful on phono inputs because of the high gain on that input. If you have noise problems, they're worth a try - if not, don't worry about it.

Rich, thanks for he quick reply. Would this matter even on AUX or FM input? Doesn't switching to one of those take the phono stage off line or can the noise bleed through because of the high gain?

 

[RichPA]

Rich, thanks for he quick reply. Would this matter even on AUX or FM input? Doesn't switching to one of those take the phono stage off line or can the noise bleed through because of the high gain?

It can matter, but that's less likely because the gain on those inputs is not as great. I have owned preamps that benefited from shorting plugs on all the unused inputs (an old B&K, for example), but it doesn't seem to matter on any of my current gear. It is easy to make your own shorting plugs from cheap phono plugs from Radio Shack or elsewhere and give it a try. Just don't put shorting plugs in any outputs!

 

[Bigears]

Good info thanks. I made some shorted RCA's and even though I don't have a noise problem, I'll plug em in.

 

[applesauce]

If the shielding on internal wiring is marginal, shorting un-used inputs can sometimes reduce crosstalk into the active input. Shorting phono inputs is often done when measuring phono preamp noise because it gives lower numbers than leaving them open. However, it is really cheating, because the effective noise level is dependent on the inductance reactance of the phono cartidge on the input, which goes up with frequency. In other words, you get more hiss with a cartridge on the phono preamp input than with a shorting plug.

 

[MatthewK]

My Marantz 2285B shorts the two "Aux" inputs when listening to the phono. I discovered this when my DVD player went silent because the receiver was switched to phono - even though it was off, and the DVD outputs were running to the TV via a splitter.

 

[theophile]

My understanding is that shorting an input prevents the unused pcb acting as an antenna,thereby lowering the overall level of circulating RFI.
Am I correct?Am I completely talking through my hat?
Dunno.:scratch2:

 

[applesauce]

I wouldn't say that you are talking through your hat. It could very well be that many pieces of audio equipment behave as you have suggested. One problem with audio equipment is "hot-rodded" designs. These are designs that are broadbanded for specmanship purposes with no regard for real world considerations, such as RFI susceptability. In other words, they a poor designs! Good conservative audio design practice shouldn't require the shorting plugs. OTOH, there is a lot of "high end" junk out there.

 

[restorer-john]

Shorting plugs are a very useful and the better the design, the greater the improvement will be if you use them. Poor designs are noisy anyway and crosstalk is bad enough that shorting unused inputs doesn't help. Unloaded inputs are a bad idea regardless of the design. With DC fet input high gain integrateds the shorting plugs prevent clicks when going through unused inputs. I use them on all phono inputs as the phono stage is generally powered up and producing noise, more noise without a cartridge on the input and that can actually degrade the line level inputs through crosstalk and coupling.

 

[alexkerhead]

Hummm, I didn't know this, now I am going to go make some shorting plugs!

 

[Duffinator]

I have and use phono shorting plugs for all my gear that have two phono inputs as I only use one of the inputs. I don't know if it makes a difference or not.

 

[Sonytubes]

How To

How do you make shorting plugs for phono using dispensible rca plugs?
Just cut the wire and plug in individually??

Thanks

 

[LBPete]

Here you go. All ready made.

- Pete

 

[chillwolf]

The shorting plugs also do another service, keeping your unused inputs clean.

 

[markn2wae]

Shorting plugs "fixed" hum problem on 1000A.

My Sansui 1000A had a strange problem when going from tuner to phono 1, randomly the left phono channel would get a strange hum on it and I used to lower the volume and switch back and fourth 1 or 2 times to clear the problem.

Then one day I accidentally dropped the tone arm while trying to cue a tick or pop to see the location (motor was off) and the left channel started humming.

It seems that a high transit signal hitting the left phono channel tends to "lock up" the input amp and temp. cause a hum problem.

The phono stages are solid state using germanium transistors (I would like to bias them for low noise silicon but haven't figured out how yet) and when going from tuner to phono 1 you have to go though phono 2 first, that is where I put my "home made" shorting plugs (just the ends of a cheap cable with the shield and center twisted together)

Works like a charm, no more "hum" problems.

Going from tuner to the "open" phono 2, then to the "loaded" phono 1 seems to be the problem cause, and the shorting plugs fixed this, otherwise everything works normally.

The phono stages where recapped and the switch was checked out to be OK and was de-oxed" with no change.

Mark T.

 

[Old1625]

I'll give my $.02 here and say that the shorting stubs are a good idea as protocol in audio practice as far as unused inputs are concerned. Most of us are apt to ignore this, but it is something that shouldn't be, as a result of such negligence can come up suddenly and hit the careless audiophile in the back of the head.

Other things that some of us may consider so much rigmarole and decorum are such practices as making sure that all equipment is unplugged from an alternating current power supply before making changes to audio/control/rf connections....

When hooking up any gear I make sure that all signal interconnections are secure in both active and return (ground) connections before doing any power connections. This is all merely "common" sense in my book. :thmbsp:

 

[KentTeffeteller]

Hi,

McIntosh uses the shorting plugs in the unused phono input. Cuts down on crosstalk, hum, and noise. Some turntable interconnects/cartridges are more hum prone than others.

 

[thinker10]

Would it better to use a "47 KΩ resistor" dummy plug instead of shorting them out ?

Just asking !