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Author Topic: Wharfdale EQ specifies balanced w/ ground disconnected on one connector?!?!  (Read 9458 times)

Rich Barrett

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I'm new to professional audio and all the technical intricacies that comes with it - that said I just bought a used Wharfdale WPG-331 graphic eq to pull down some specific frequencies on my nasally sounding voice. I do a talk show podcast.

That said, the manual specifies the BEST way to connect inputs and outputs to the unit is to make a TRS cable BUT leave the shield / ground disconnected on the Wharfdale input side. On the output you do the opposite; leave the ground disconnected on the side that plugs into whatever device the Wharfdale is outputting to. (the XLR outs get the same treatment)

They go on to say if you hear line hum go ahead and connect the shield / grounds.

This makes no sense to me as I thought the 3 conductor balanced cable was by design the way to reduce / eliminate line noise by equalizing all unwanted potentials? Is this method unique or pretty normal when connecting professional audio gear such as eq's?

Thanks!
« Last Edit: October 18, 2013, 01:16:27 pm by Rich Barrett »
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John Roberts {JR}

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 :o :o :o

Not a good sign for the integrity of the rest of the audio path.

JR
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When in doubt do what's right.

Rich Barrett

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:o :o :o

Not a good sign for the integrity of the rest of the audio path.

JR

Not a good sign? Please explain ...

And my signal path is;
out: Yamaha 02R (insert) -> Ebtech LLS-8 -> Wharfdale
in: Wharfdale -> Ebtech LLS-8 -> Yamaha 02R (insert)

the ebtech is a transformer based line level converter (ts -> trs + trs ->ts) and noise eliminator.
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Tim McCulloch

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Not a good sign? Please explain ...

And my signal path is;
out: Yamaha 02R (insert) -> Ebtech LLS-8 -> Wharfdale
in: Wharfdale -> Ebtech LLS-8 -> Yamaha 02R (insert)

the ebtech is a transformer based line level converter (ts -> trs + trs ->ts) and noise eliminator.

JR is referring to what has been called "the pin 1 issue."  You can read more here:  http://audiosystemsgroup.com/Pin_1_Revisited.pdf

and here:  http://pin1problem.com/
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Geoff Doane

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This makes no sense to me as I thought the 3 conductor balanced cable was by design the way to reduce / eliminate line noise by equalizing all unwanted potentials? Is this method unique or pretty normal when connecting professional audio gear such as eq's?

Thanks!

The simple answer is "It probably doesn't matter".

The long answer is much more complicated.

A balanced line has two conductors that have equal source impedances.  When connected to a differential ("balanced") input, any signal that is common on the two lines gets cancelled out.  With some luck, your desired signal is different on the two lines (they don't even have to be equal and opposite polarity, but often are) and the noise is common, and therefore is eliminated.

The shield is only there to prevent RF (radio frequencies) from getting into the audio lines.  The differential circuitry may have a harder time cancelling out those extreme high frequencies.  The problem is that the shield might also cause a small current to flow from one audio ground to the other, causing hum.  This possibility has been largely eliminated in modern equipment designs (pin 1 problem), but could be a problem with older legacy gear.  The shield is also used as the return path for phantom powered microphones, although that is not a factor for your setup.

20 years ago, good engineering practice dictated that you only connect shields at one end, and you only ever used balanced inputs and outputs.  I've worked on projects that were designed this way, and the whole system was remarkably free of hum once it was finished.  Our particular Engineering Dept. standardized on only connecting the shields at the destinations.  I suspect it doesn't matter too much which end you connect, as long as you're consistent.  These days, if all the gear is properly designed in the first place, shields can be, and often are, connected at both ends.  This does provide better RF shielding, at least in theory.

GTD
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Rich Barrett

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JR is referring to what has been called "the pin 1 issue."  You can read more here:  http://audiosystemsgroup.com/Pin_1_Revisited.pdf

and here:  http://pin1problem.com/

Well I read the paper from audiosystemsgroup and it seemed to me that ALL older gear was subject to this, including microphones!?

Would there be any benefit to NOT connecting the shield on all my TRS cables to the internal ground pins but instead jumpering them straight to a chassis ground? say drilling a ground lug on the back panels of my equip? That at least should eliminate the shield becoming an antenna that feeds back to the circuitry.

Or does it not matter because the internal traces aren't being RF filtered like the article recommends?
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John Roberts {JR}

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Well I read the paper from audiosystemsgroup and it seemed to me that ALL older gear was subject to this, including microphones!?

Would there be any benefit to NOT connecting the shield on all my TRS cables to the internal ground pins but instead jumpering them straight to a chassis ground? say drilling a ground lug on the back panels of my equip? That at least should eliminate the shield becoming an antenna that feeds back to the circuitry.

Or does it not matter because the internal traces aren't being RF filtered like the article recommends?

There is no simple tweak for legacy gear with pin one problems. Often there are layout and even circuit design issues, not very easy to modify after production.

For now just follow the advice of the manufacturer, and if the product sounds bad, try the easy options, and if nothing easy works consider replacing with something better designed.

As hard as it might be to sell poorly designed legacy gear it will be even harder to sell after you drill holes in it and experiment with grounds.

JR
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Rich Barrett

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There is no simple tweak for legacy gear with pin one problems. Often there are layout and even circuit design issues, not very easy to modify after production.

For now just follow the advice of the manufacturer, and if the product sounds bad, try the easy options, and if nothing easy works consider replacing with something better designed.

As hard as it might be to sell poorly designed legacy gear it will be even harder to sell after you drill holes in it and experiment with grounds.

JR

Thanks guys! One last question; about what years did the higher end manufacturers stop making devices that suffer from pin 1 ? for example 2000, 2001, 2002?
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Tim McCulloch

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Thanks guys! One last question; about what years did the higher end manufacturers stop making devices that suffer from pin 1 ? for example 2000, 2001, 2002?

There hasn't been a universal "stopping."  There is still some product being made that exhibits the Pin 1 Problem.  You can't pick a date and think the problem has been eliminated.

Shop where you have return privileges, or better yet can take your gear in and hook up the item you're interested in.  If you're located somewhere that this is impossible, post questions here about specific items before buying.
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Art Welter

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There hasn't been a universal "stopping."  There is still some product being made that exhibits the Pin 1 Problem.  You can't pick a date and think the problem has been eliminated.
I had some Rane digital delays purchased in 1997 that would hum or buzz no matter what was done with pin 1, the only solution being isolation transformers.

Looking at their RaneNote written in 1995, revised in 2002, might be they "got with the program" sometime early this century.

I still won't be getting rid of my shield lifts and isolation transformers, but need to use them less often as old gear "fades away".

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