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Author Topic: Ying outputs, was I really that wrong?  (Read 6437 times)

John Roberts {JR}

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Re: Ying outputs, was I really that wrong?
« Reply #10 on: January 04, 2016, 09:41:42 am »

This comes down to "can you do it" vs. "should you do it". As you've already determined you "can" do it for this particular situation. No smoke was released and you didn't hear audible degradation.

"Should" you do it, NO. Just because some manufacturers anticipate and protect against such questionable connections, don't ASSume you can always do that. Someday you might encounter an unprotected design and it won't work, might even harm the poor thing. 

I recall putting additional dedicated mono outputs on some Peavey mixers.

JR

PS: A custom Y adapter with added series resistors (say 1-2Kohm per leg) could protect weak outputs and still deliver reasonably low source impedance. Ironically products low on the value spectrum often use larger impedance build out resistors, mainly because they can't drive 600 ohms with the wimpy GP op amps, not some grand plan. 
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Geoff Doane

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Re: Ying outputs, was I really that wrong?
« Reply #11 on: January 04, 2016, 09:51:34 am »


Because Mackie outs are impedance balanced and the signal is mostly mono I can Y them with out any problem or risk of damage.


Impedance balanced means that the "low" side has an impedance to ground, but is not driven.  You're still connecting two driven signals together through a rather low output impedance, and that's what could cause distortion (I have heard it happen), although any damage is less likely.

However if it's really "mostly mono", then why not just use one output? 

Your co-worker was correct that it is not "best practice".  It's somewhat questionable whether it was worth making it an issue however.  For the record, I routinely Y a pair of e604s used for congas, and nothing bad has happened yet.  It's a much better solution than having to drag out a 32 channel console instead of a 16  8)

GTD
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Scott Helmke

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Re: Ying outputs, was I really that wrong?
« Reply #12 on: January 04, 2016, 10:04:39 am »

I just had the 1202 VLZ schematics handy, and there have been some different versions over the years.

But the Control Room outputs do have 120 ohm resistors. So no real problem, aside from "showing bad form, old boy".
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Riley Casey

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Re: Ying outputs, was I really that wrong?
« Reply #13 on: January 04, 2016, 10:05:15 am »

So to sum up  :o , its not a good idea to parallel actively driven outputs because they will likely cause distortion when driven to any significant level and in the case of poorly designed equipment might damage the output stages.

Real question in this instance I would propose is why bother?  What is the value of summing L & R when trying to drive a subwoofer feed?  Unless you have some VERY unusual program material the low frequency component of the program is unlikely to be hard panned.  Left OR right will have all of the under 100 hz information needed to ensure that the sub feed is delivering the goods.  You may  well need some additional gain after the mixer output but summing probably wasn't worth the effort.

Jim McKeveny

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Re: Ying outputs, was I really that wrong?
« Reply #14 on: January 04, 2016, 10:05:30 am »



A TRS Control Room output to a mono XLR? Without pinouts we have no clarity.
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Steve M Smith

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Re: Ying outputs, was I really that wrong?
« Reply #15 on: January 04, 2016, 10:09:15 am »

I just had the 1202 VLZ schematics handy, and there have been some different versions over the years.

But the Control Room outputs do have 120 ohm resistors. So no real problem, aside from "showing bad form, old boy".
I just found the same thing on the 1604 circuit so yes, I would have no problem parallel connecting the outputs.
 
Note, every output has these resistors.  Aside from summing together, they are good to protect an output from short circuits to such as putting a two pole 1/4" jack into a TRS output which will ground the ring connection (although this is usually just a 120 ohm resistor to ground).
 
http://bmamps.com/Schematics/Mackie/Mackie_1604-VLZ_16_channel_mixer.pdf

A TRS Control Room output to a mono XLR? Without pinouts we have no clarity.
In the case of the Mackie, the R connection is just a ground compensation resistor.


Steve.
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John Roberts {JR}

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Re: Ying outputs, was I really that wrong?
« Reply #16 on: January 04, 2016, 10:14:30 am »

We already know it didn't blow up.

Not best practice... Lets not encourage people to do this.

JR
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Tom Bourke

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Re: Ying outputs, was I really that wrong?
« Reply #17 on: January 04, 2016, 11:22:05 am »

We already know it didn't blow up.

Not best practice... Lets not encourage people to do this.

JR
I admit not best practice and not something I normally do.  Certainly not for normal gigs or with other gear.  However in THIS case with an older version Mackie, that I know to have robust outputs, and to just add some thump to a pre-function room for 4 hours. I felt a mono sum with a Y cable was acceptable.

When I set it, I did add to the board tape a note not to solo anything.  In this case no need to solo anyway. 

This was more of a political problem.  I was promoted very fast because I am the go to guy for technical problems and troubleshooting.  My real failure was not anticipating the shit-storm from getting "caught" on a technical compromise.
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Tom Bourke

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Re: Ying outputs, was I really that wrong?
« Reply #18 on: January 04, 2016, 11:36:35 am »

PS: A custom Y adapter with added series resistors (say 1-2Kohm per leg) could protect weak outputs and still deliver reasonably low source impedance. Ironically products low on the value spectrum often use larger impedance build out resistors, mainly because they can't drive 600 ohms with the wimpy GP op amps, not some grand plan.
I do have such a Y cable in my personal pile of gak. It dates back to my first couple years in the biz.  I could not afford much gear so I made due.  The above cable would give me a mono sum and then on the parallel out of the sub amp I put a capacitor shorting pin 2 and 3 to knock the highs out of the subs.  Ahh those were the days, heavy iron amps and Radio Shack.

These days I don't bring much more to work than a personal laptop, Fluke meter, and a nice network cable tester.
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John Roberts {JR}

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Re: Ying outputs, was I really that wrong?
« Reply #19 on: January 04, 2016, 12:08:07 pm »

I can't opine about the politics, but in general when a subordinate backs me up by bringing something like that to my attention, I thank him for having my back. Of course how he presented that information may make a difference.

Maybe make him your technical guy and continue your focus on management.

Good luck, politics can be a PIA, while should be less of a hassle the smaller the organization.

JR

PS: Maybe show you custom Y cable to you critic (or give it to him) to let him know that you know too.
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Re: Ying outputs, was I really that wrong?
« Reply #19 on: January 04, 2016, 12:08:07 pm »


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