wiring up headphone cues. a few questions...

Well I'm doing the layout for a headphone cue system and I am trying to remember a few things. Using a regular power amp we have unbalanced L and R. So I am planning to use a 4 pin XLR at the wall in the live room. Then make a breakout box that goes from 4 pin to several 3 pin TRS jacks for headphones or maybe XLR and putting XLR connectors on the headphones. Anyway I know the grounds get shared to get down from the 4 pin to 3 pin.

1. which pin gets L hot and which pin gets R hot?

2. what would be the easiest way to add a volume control? I am thinking a stereo pot before the TRS jack. It would be passive but would be inexpensive or is that a bad approach?

When you say you have "balanced", that refers to input to your headphone amp. Balanced can be either XLR or TRS. Your headphones too are TRS, but is usually an 8 ohm (amplified). If you want different individual mixes for each set of cans, that would require a different setup.
I just re-read your post and I think I see what you are trying to accomplish.
You have unbalanced going to your headphone power amp. What kind of output connectors are on this amp? If they are 1/4" then they are TS. If thats the case you can use a standard 3 pin XLR. the ground would be common to left and right, so for the 3 pin XLR, you would have left, right, and ground. I use a similar method, with line level from my board in the control room to the wall panel in the tracking room which is an XLR (male) the headphone amp is plugged in to that, and all the headphones are plugged in to the headphone amp.

[quote author="CHANCE"]When you say you have "balanced", that refers to input to your headphone amp. Balanced can be either XLR or TRS. Your headphones too are TRS, but is usually an 8 ohm (amplified). If you want different individual mixes for each set of cans, that would require a different setup.[/quote]

you misunderstood it but coolio.
lets use real world items.

Say I have a crown D-60 power amp. I am using that the feed the studio cues.
Inputs to the d-60 are balanced.
Comming out of the D-60 I have 2 unbalanced signals one is the left channel and one is the right channel this would normally go to a set of speakers but is going to say cue 1.

Ideal Situation would be to feed that into a 4 pin XLR which would be on the wall plate. From the wall plate have a break out box that has 4 pin on the input and multiple TRS or XLR jacks on the output. THe headphones themselves may end up with XLR connecotrs on them.

going from 4 pin XLR to 3 PIN would have the grounds of each signal being shared.

so on the TRS/XLR jack which pin gets left hot which pin gets right hot?

2. is it possible to add a stereo volume pot before the TRS jack on the breakout box so that the person in the studio has some sort of basic control of over all level. I know doing this would have it passive but it's better then nothing...

does that make more sense now?

I edited my post while you were posting. LOL

so pin 1 is ground

pin 2 Left hot?
pin 3 right hot?

XLR's used for an input usually use pin 2 for hot. It would be a simple thing to add an L-pot for the output to the cans. I first used a cheap Rolls headphone amp (I think that was the name of it) it was only $25.00. It had 4 inputs (2 stereo) with 6 headphone outs. Each out had its own voulume control. I now remember what I didn't like about it. If you plugged in a 1/4" TS plug, you would fry something inside. Thats exactly what someone did. They had their own cans with a 1/8TRS plug, but their adaptor was 1/8 to 1/4 TS, and it fried. There was even a warning on the front panel.

is it possible to add a stereo volume pot before the TRS jack on the breakout box so that the person in the studio has some sort of basic control of over all level. I know doing this would have it passive but it's better then nothing...

Click to expand...

Passive L-Pad headphone boxes work ok til they get burn spots on the L-Pads.
Then they get problamatic.

Usually, the trouble starts when the musicians turn them way down and you turn the cue amp way up=)

Things are a little clearer now. At your output source (D-60 amp) determine first where your ground is. (that will be common to your left and right) then you can use jumper wires to determine your left and right by experimenting. Since the ground is common if one wire is not right you will know the other one is. It might be helpful to feed an audio signal to only one side of your power amp so you will know what the source is sending out. When you discover which is which you will then know how to wire accordingly.

Be sure to add 10 Ohm resistors or higher between the breakout box input jack and the headphones output jack on both left and right connections. This will keep a pair of shorted phones (or plugging in a T/S jack) from taking out your power amp. The wattage rating should be high enough to safely sink the amp's output (see the earlier post about frying something).

Excellent point. The Rolls headphone amp I used to have, did not have this. Instead they put a warning sticker to insert TRS only