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[Tom Bourke]

Had a co-worker go off on me over a setup for the new years festivities.  The venue was a large Las Vegas strip hotel with multiple ball rooms.  One of the smaller ballrooms was a "pre-function" area with bars and themed photo areas.  Simple audio needs, premixed "DJ" tracks off a laptop, main ball room feed and maybe an announce mic.  Outputs were L,R, Fill, Sub, Alternate room.  PA was large A level powered speakers with internal DSP that could take full range LR+Sub.

For a mixer I had a Mackie 1202 or something much larger.  I chose the 1202 because it had plenty of inputs, simple to use for the intended opp, and I could role it in on a cart with the cables.  All told I needed a stereo and 3 mono post fade outs with volume knobs.  I chose LR for the mains, aux 1,2 for fill and alternate room, and 'Y'ed the control room outs for sub. The system sounded fine and was signed off on by the powers that be.

A couple days later a co-worker starts ripping me a new one over "never Y two outputs!"  This turned into a huge fiasco.  For the record my position is a couple notches higher than his and I tend to think more like our managers "get it done safe and efficient."

When I chose to Y the outputs I was thinking:

I need another isolated mono out.

The control room outs are buffered from the main LR and the knob is next to the LR knob.  Should make a nice sub-woofer feed.

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

I don't care about any added distortion because the sub-woofer processing will filter out most of it anyway.

I have several days to change it if it does not work.

Listening tests show it sounds good, done, onto the other hundred things on my todo list for the day.

So, was I wrong?  Did I commit a "Cardinal sin" by Ying the control room outs?

In hind sight, yes he caught me on a technicality.  However I stand by that the risk of damage was zero and the out come served the needs of the gig well.

[Steve M Smith]

I would have thought that most ouputs would have some sort of series resistor to prevent short circuit damage anyway so they should sum together o.k.

If not, a few low value resistors in the Y lead should sort it out.


Steve.

[Keith Broughton]

The control room outs are buffered from the main LR and the knob is next to the LR knob.  Should make a nice sub-woofer feed.

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

I don't care about any added distortion because the sub-woofer processing will filter out most of it anyway.

Control room out...(good point).

No risk of damage...how did you arrive at that conclusion? (not a good point)

added distortion....I'm looking for the processor that filters out added distortion! (very bad point)

[Jim McKeveny]

"Y" to split, or "Y" to sum?

[Jordan Wolf]

If you used the wye to split the signal, I see no issue; physical isolation (i.e. transformer) may be a nice extra step since most likely powering from a different AC source.

I would have not used the control room out since soloing affects the output signal. Go mono (Main Left only) for main and use Main Right for sub feed; that still gives you independent level control and you can control how much goes to the sub by using the pan knob.


- Jordan Wolf

[Ivan Beaver]

The biggest issue for not Ying outputs is that the output impedance of each channel will load down the other channel and vice versa.

Yes you will have some harmonic distortion-due to the extra load.

Yes you can have other types of distortion-freq response etc because the coupling caps are designed for a particular load and when that load is well below expected, the low freq can roll off.

However the biggest issue could be actual DAMAGE to the output transistors or ICs.

They are not designed to drive a load rated at their output impedance, so they could fail.

SURE-it might "kinda work" for a little while, but it is NOT something you want to do.

You might get lucky and get away with it, but it is a VERY BAD idea.

[Jim McKeveny]

The biggest issue for not Ying outputs is that the output impedance of each channel will load down the other channel and vice versa.

Yes you will have some harmonic distortion-due to the extra load.

Yes you can have other types of distortion-freq response etc because the coupling caps are designed for a particular load and when that load is well below expected, the low freq can roll off.

However the biggest issue could be actual DAMAGE to the output transistors or ICs.

They are not designed to drive a load rated at their output impedance, so they could fail.

SURE-it might "kinda work" for a little while, but it is NOT something you want to do.

You might get lucky and get away with it, but it is a VERY BAD idea.

We still do not know if this was a split or sum, so we are still in speculation mode.

However, if it was a split......and a single split not daisy chain, our pal JR has let us know that knowledgeable mfrs. anticipate 'streme apps by the end-user, because building in mild overcapacity is always cheaper than enduring client-caused failure with commensurate warranty costs & mfr. rep damage.

My advice to the OP is to always expect way more I/O than spec'd.

[g'bye, Dick Rees]

We still do not know if this was a split or sum, so we are still in speculation mode.

Jim...

Read the thread title again...

[Jim McKeveny]

Jim...

Read the thread title again...

It's the stereo/2 chan. thing that leads me here. With differential diagnosis assume nothing.

Was a TRS Stereo Control Room output sent to mono subs? That would be backass by our standards, but could be called a "Y". We dunno.

Like a lawyer, we have to parse every
syllable. It's an affliction, I admit

[Scott Hofmann]

It's the stereo/2 chan. thing that leads me here. With differential diagnosis assume nothing.

Was a TRS Stereo Control Room output sent to mono subs? That would be backass by our standards, but could be called a "Y". We dunno.

Like a lawyer, we have to parse every

Parse it again.... "sub" is singular!
syllable. It's an affliction, I admit

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