RCA and XLR shorting caps...whats the deal with those?

[Sokel]

Iis that with the open/shorted input selected for output? Or another input selected for output - one with a signal connected?

This is all the inputs shorted except the one used for sending signal,that's connected with the DAC.

 

[Sokel]

Iis that with the open/shorted input selected for output? Or another input selected for output - one with a signal connected?

Oh,I see you're asking a different question.
So,all inputs are shorted except the one connected to the DAC/generator and the output corresponds to this input.

All other (shorted) inputs selected have more or less the same effect,maybe they look a half dB better.
Note that inputs are controlled by relays.
Nothing to worry about and I expect the effect to be less at more recent gear.

 

[IEales]

-3dB overall, but -20dB @ mains 50Hz

About -3dB less noise but at this level and structure I wouldn't loose my sleep,it's vastly inaudible.

About 15 to 20db less @ mains Hz and harmonics with the inputs shorted. Not a problem with analog tape but might cause some issues on 20- or 24-bit sampling adding just enough level to cause some artifacts. A 96- or 128-input console would build the level a fair bit.

 

[Sokel]

-3dB overall, but -20dB @ mains 50Hz


About 15 to 20db less @ mains Hz and harmonics with the inputs shorted. Not a problem with analog tape but might cause some issues on 20- or 24-bit sampling adding just enough level to cause some artifacts.

Yes,but what you see is not on a bench on ideal conditions,it's rather as it sits on the rack as in a real life setup.

And I have seen this or comparable mains interference affecting gear like SOTA DAC,etc just by crossing a mains cable near them,or bad cable routing,or stuff that interfere with gear like led lights,motors,HVAC (the last two can create havoc if at the same electrical line),fans,etc.

Edit: what can create the absolute mayhem down there,regardless the gear are EMI/RFI emitters,like a phone receiving a call for example if put VERY close.
The whole noise floor literally dances to it,it's funny to watch it.

 

[IEales]

Yes,but what you see is not on a bench on ideal conditions,it's rather as it sits on the rack as in a real life setup.

And I have seen this or comparable mains interference affecting gear like SOTA DAC,etc just by crossing a mains cable near them,or bad cable routing,or stuff that interfere with gear like led lights,motors,HVAC (the last two can create havoc if at the same electrical line),fans,etc.

Not sure what you are getting at.
If it's quieter with inputs shorted, why not?

Acid test for any studio is all used channels at 0dB and monitors on S T U N. Anything but thermal rush is unacceptable.

 

[Sokel]

Not sure what you are getting at.
If it's quieter with inputs shorted, why not?

Acid test for any studio is all used channels at 0dB and monitors on S T U N. Anything but thermal rush is unacceptable.

All I'm saying is that I guess it's ok to use it,I do for my unused inputs to tell the truth (even at nicer gear which the effect is not as prominent to this ancient relic but close to zero,as they are not class A to amplify anything close to it if not taken cared off)

I guess it would be far more important for pro use in a studio,as all the rest.Measurements are mandatory there as far as I know,so everything will be picked up and fixed on the way.

 

[Sokel]

Oh,and about XLR connections.
What makes the big difference is if the shell of the connectors is grounded or not.
I have seen 20dB more noise all over with the shells unconnected immediately dropping just grounding them.
The same but less even if they are terminated to other gear,shell is probably working far better as a shield when grounded.

It's probably the same effect with PCB's heatshinks which must always be grounded so they shield the elevated components mounted on them.

 

[antcollinet]

Oh,I see you're asking a different question.
So,all inputs are shorted except the one connected to the DAC/generator and the output corresponds to this input.

All other (shorted) inputs selected have more or less the same effect,maybe they look a half dB better.
Note that inputs are controlled by relays.
Nothing to worry about and I expect the effect to be less at more recent gear.

Sorry - I'm still not clear, you don't state which of the inputs has the shorting plug added removed. Are you measuring the output connected to the input on which you change the short/no short.

Becasue if so this makes no sense. You would obviously not output a channel with the plug fitted - we need to know the impact on a different input to the one having the plug fitted removed.

So (EG) iinput 1 open. Inputs 2, 3, 4 shorted. Connect 4 to output. Measure with 1 open and 1 shorted.

 

[Sokel]

Sorry - I'm still not clear, you don't state which of the inputs has the shorting plug added removed. Are you measuring the output connected to the input on which you change the short/no short.

Becasue if so this makes no sense. You would obviously not output a channel with the plug fitted - we need to know the impact on a different input to the one having the plug fitted removed.

So (EG) iinput 1 open. Inputs 2, 3, 4 shorted. Connect 4 to output. Measure with 1 open and 1 shorted.

I thought I should do it more life-like that's why I measured it this way.
So,as you asked:

All inputs shorted -output corresponds to 5 input

All inputs except 1 is shorted -output corresponds to 5 input


Difference is smaller but still there as it seems.

(I expect this to be not the typical case though.We are talking about a pre with 5 inputs plus a passthrough I/O and 2 outputs plus 2 tape out,lots of chances for noise to creep in .But I guess it doesn't hurt to short the unused inputs )

 

[antcollinet]

So,as you asked:

Thanks - that was above and beyond.

And I'm surprised there is even this much change. It llooks to be all 50Hz and harmonics. Are you in a 50Hz mains region?

 

[Sokel]

Are you in a 50Hz mains region?

Yes,Europe.It's all mains noise,it looks like if caps have drained,or transformer saturation,doesn't it?
It's neither as I have recaped it and trafos (it has 3) is more than enough.
Just plain,high-ish biased class A pre,but with the noise down there it's insignificant.

 

[IEales]

FWIW, when I had analog front end with mechanical switches and level controls, I back-shorted all unused inputs and regularly exercised the switches and pots.

Some studios had an 2nd engineer do the same to pots and switches regularly to find any failing parts before the paying customer.

 

[Sokel]

Looks like asking for a drop forge when all you need is a tack hammer.

Goes without saying that I had to do something about those mains noise:

I Vishay'd (TO-220 diodes,the old ones had probably seen too much peaks of inrush current given the 30k uF of caps in there) and Wima'd (small polystyrenes right next to transistors as it does not use regulators) the hell out of it.

Not bad,it can do better I think.

At the thread subject,I tested more stuff and it seems that shorting works,more or less (for folks that read first time,I'm talking strictly INPUT,NEVER OUTPUT)
Audible?Who knows,depending on the gain structure I suppose it can be at some cases.

 

[IEales]

Well done!

When I was @ AMS-Neve we experimented with adding noise and distortion @ the -16bit level on 20bit audio and 24 & 32 bit processors. Not everyone could hear it, but some could. The perceived change depended odd or even distortion.

 

[GabrielPhoto]

Thanks for all the tests. So it seems there is a measurable difference but unlikely for me to actually hear it in real world scenarios

 

[IEales]

unlikely for me to actually hear it in real world scenarios

It's always been my contention that everything you can do to minimize non-program noise increases the realism.

In our wired world, there are innumerable radio frequencies buzzing around. Sometimes they create interference signals that frequency modulate.

Hook your pre-amp up to a distortion analyzer and view the output spectrum. If you don't have the tools, put your ear right on the drivers.
Anything there will ± with the program.
Then back short all the unused inputs. In an electrically noisy environment, there may be a considerable difference on some equipment.

 

[GabrielPhoto]

That makes sense..
Is it 100% safe with my 3800h AVR to short all inputs only?
I also got other stuff with unused inputs like Fosi v3 mono, Aiyima 07 max, etc

 

[IEales]

Analog inputs are safe to back short - w 600Ω for phantom powered mic.

Digital inputs likely won't benefit, but I never tried.
If I had a TosLinks with busted doors, I'd probably tape them over or insert a dummy but that's probably over the top.

 

[GabrielPhoto]

S

Analog inputs are safe to back short - w 600Ω for phantom powered mic.

Digital inputs likely won't benefit, but I never tried.
If I had a TosLinks with busted doors, I'd probably tape them over or insert a dummy but that's probably over the top.

Something like this for some adder bling besides Shorting?

Amazon.com

 

[IEales]

More like this: Gold Short Caps

I'm not much for bling... "As Simple as Possible and No Simpler" ...the missus has often said I'm boring