Mixers/Consoles Mystery Low Monitor Level (with answer!)

JD

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Jan 1, 2005
Location
North Wales PA
So, two days ago I did a gig with the choral group I sing with. During setup, I took a fall and hurt myself, which is the excuse I'll used for this amateur mistake I made during setup ;) We had almost no monitor feed during the show, which is unusual as I keep things well maintained and tested. Someone took a picture during the show to catch the reflection of the stain glass windows on the laptop. The next day I saw the picture online and also saw the answer to the problem! I could have smacked myself upside the head! Hint: It has nothing to do with settings.
6-10-17.jpg
 

EdSavoie

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Oct 19, 2016
Location
Windsor, ON, Canada
Is that output only partially inserted?

If you hadn't said it that it wasn't the settings, I would have guessed the subgroups were unpatched. We've got the (Similar) SX2442FX Eurodesk and run our monitor signals out of sub 1-2.
To be fair, there's half a dozen ways to run the monitors out of these boards :p
 
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JD

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Jan 1, 2005
Location
North Wales PA
We have some observant people here!
Yup, everything on this system is TRS, so the loop jack to the monitor EQ was only inserted to the first click. Thus it was T-R with the other T & R open!
And yup, about 6 Db down! A real amateur mistake if I say so myself!
 
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JD

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Jan 1, 2005
Location
North Wales PA
The number of jobs I've closed with some variation of "pushed the plug back in properly" over the last few years...

I guess we proved that this desk isn't impedance balanced, probably it's electronically balanced, transformers don't really fit with that price point...
Yea, with true transformers there would be no output. (or some tinny rasping 30 Db down.) There was enough there to make you believe things were working (rush-gig, no sound check) but once we were up there singing it was like "Oh Sh**!"
 

Chris15

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Jul 15, 2005
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Sydney, Australia
In most applications though, don't you connect the centre tap of an output transformer to ground to reference it (or AC couple a virtual ground)?
If that were so, I'd still expect 6dB down...
Never, ever, should the centre tap on an input be grounded though ;)
 

JD

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Joined
Jan 1, 2005
Location
North Wales PA
In most applications though, don't you connect the centre tap of an output transformer to ground to reference it (or AC couple a virtual ground)?
If that were so, I'd still expect 6dB down...
Never, ever, should the centre tap on an input be grounded though ;)
I remember inputs on a mixer being center-tapped to insert the phantom voltage. (Most modern mixers just use a set of resistors.) Outputs usually floated, and then power amps that used plug-in transformers were usually floated. In this case, the patch was actually between the output of the graphic (transformerless) and the input of the QSC power amp (also transformerless.) Half the voltage, which causes the speakers to only draw half the current as well, Presto ! -6Db
 
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FMEng

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Mar 31, 2008
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Tacoma, WA
In most applications though, don't you connect the centre tap of an output transformer to ground to reference it (or AC couple a virtual ground)?
If that were so, I'd still expect 6dB down...
Never, ever, should the centre tap on an input be grounded though ;)
Almost never does a line output transformer have a center tap. The whole point of a transformer balanced output is to have galvanic isolation. A quality transformer is a beautiful thing for driving long lines or making connections between equipment on different AC sources.