Proper cable wiring question

THX1136

THX1136

Bonehead
I've searched here and elsewhere and have read conflicting information. A friend asked me to do up a cable for him and I wanted to double check my memory to reassure myself I have it right.

The cable is connecting a headphone out of a piece of gear to a mono input of a mixer. He wants both the left and right portions of the audio to end up at the input of the mixer. I would do the cable with the tip & ring to tip; the sleeve to sleeve.

What I've read is that - or tip to tip; ring/sleeve to sleeve, or don't connect the ring to anything. I think my initial thought is the more correct way to accomplish what he wants the cable to do since both the output and input are unbalanced. I'm guessing the conflicting info I've read is more concerned about unbalanced to balanced connection issues.

I personally don't care about the unbal/bal issue as it seems to not be in play in this situation. Where I'm becoming unsure is the conflicting info I've read and somewhere, in the back of my mind, I seem to remember something about only split outputs, never combine inputs. Can someone enlighten my aging brain? Thanks!
 
I don't know if it's a good idea to combine signals, but out of the opions your method is the correct way to do it.

Left channel is on tip, right channel is on ring.
If you connect either of those to sleeve you're just grounding a channel away.

Whether the mix input is balanced or unbalanced, you want both your signals to go to input tip.
 
Thanks for the input Steenamaroo. You confirmed what I was thinking about the alternate ways I read about.
 
THX1136 said:
I seem to remember something about only split outputs, never combine inputs. Can someone enlighten my aging brain? Thanks!
Click to expand...

This is correct. If you want to combine them you need to build a summing network, which is just a few resistors of the right value. Why can't he use a pair of channels or a stereo line input or a stereo aux return?
 
As to the adapter question, the hookup is already using an adapter due to budgetary restraints at the time it was set up. Due to the orientation of the jack it makes the connection unstable. Also, in my experience, adapters open up the possibility of "noise" getting into the audio. Since this is in a broadcast setting that goes out nationwide I would rather not introduce any noise into the audio (although with the compromise already made it IS open to noise pollution). At the start the program was only on a handful of stations. It has since expanded to 50 affiliates across the US.

As to the using a pair of channels or stereo return thought, I'm not sure if the extra inputs are available. A friend and I put the studio together back in late Spring of 2012 and I do not recall how much of the board was "used", so to speak. (I have not been back since we put things together for them.) We used a Mackie 1402 and with the needs for broadcast we used a lot of what was available at that time. Another factor is keeping it "one knob simple" for the producer/engineer. Boulder Sound Guy, could you give me an idea of how to go about the summing - or a link to a good source of info on that? Thanks in advance.
 
I don't know the exact values, but it's a simple matter of three or so resistors.

The 1202 has four stereo input channels plus two stereo aux returns. Connecting a 1/4" headphone output to any of those can be done with an off the shelf "insert" cable while retaining stereo. No doubt there's an off the shelf cable to go from 1/8" headphone to dual 1/4" inputs as well. I would do that or simply spend the money on a cheap DJ board to submix several stereo sources (complete with crossfader) before summing a stereo source into one channel.
 
I think just 2 resistors of the same value will do, one resistor of the same value for each signal being mixed. Haven't done this myself, but try resistors from 2kohm to 10kohm.

There will be some signal attenuation.
 
If you were talking of combining two line outputs of say a mixer then yes, it is bad practice to simply join them together.
This is is because each output should be at a low, even very low (even <1Ohm) resistance and each will try to drive the other resulting in distortion or in rare cases damage. The solution is a resistor in each line 2k7 being about as low as you want to go. Each output will then "see" about 5k and that will keep them happy.

The downside is that you have raised the source resistance and this could lead to HF loss with long leads. One fix for this is to put the combining resistors at the input, not the output end.

A headphone out is different matter since it should be able to drive a very low resistance but 100 Ohms per leg would not hurt. Lower loads, i.e. more output current almost always leads to increased distortion.

Dave.
 
If you are using a device that only has a stereo headphone output (MP3 player? phone?), then chances are any 'noise' introduced using a stereo-to-mono adapter would be unnoticeable!
 
Thanks for all the help. I think I've got it sorted out.

A question to ecc83: If I put the resistors as the 1/4" end could I just use one instead of 2? I'm thinking about just putting them inside the plug itself as there should be room. I checked on the input impedance on the 1402 and it's 10K as was mentioned elsewhere. Anyway. . . thanks again to all who contributed to the answer. I appreciate your time.
 
THX1136 said:
Thanks for all the help. I think I've got it sorted out.

A question to ecc83: If I put the resistors as the 1/4" end could I just use one instead of 2? I'm thinking about just putting them inside the plug itself as there should be room. I checked on the input impedance on the 1402 and it's 10K as was mentioned elsewhere. Anyway. . . thanks again to all who contributed to the answer. I appreciate your time.
Click to expand...

No, has to be two. But since in this instance we are talking headphone source the resistors can be at either end, whichever is the more convienient.

In the general case, where the Rs are ~2k7 they should be at the input end but even here for cables under about 3mtrs it would not really matter. Actually it would be prudent to use 2k7, at the sink end because then you have a general purpose mono'ing cable.

http://www.rane.com/note109.html Fig' 2 shows the idea but those resistors are a bit low for "consumer" grade gear, ok for headphones tho'
Ha! 'Tis early and only had one coffee! They show the circuits in boxes. Always a better way IMHO.

Dave.
 
Off topic...

Rane is a veritable treasure trove of practical info about connecting equipment, cabling, grounding, and lots of other stuff.

it is well worth the effort of reading through their resource pages.

Paul
 
+1 for PRHunt's recommendation of the Rane site for information. I've sent many a person there for a good read!

RANE NOTES

Totally off topic in this thread but their pages on compression and dynamics processing are the best I've found anywhere.

So long as we're recommending reference material, everybody doing sound should have a copy of THE YAMAHA SOUND REINFORCEMENT HANDBOOK on their shelves. It's not a book just to sit down and read--but as a reference for obscure wiring diagrams, equations for converting levels, etc. etc. it's pretty much indispensable. My copy is VERY thumbed.
 
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