HELP with designing a headphones distributor please

[sonolink]

I don't understand what you mean by "wiring the power boxes i n parallel," you'll have to draw a diagram of what you are considering.

What I meant is that in a parallel circuit, voltage is the same across all components, so you wouldn't have any voltage drop. But again, I don't know if it's possible to implement that and at the same time have the audio wiring right. In any case I think I'm going to go unbalanced

I'll draw a complete schematic with values and report back.
Thanks a lot for your time and help
Cheers
Sono

 

[MidnightArrakis]

Thanks for your input Jerry. The person that has asked me to build this for him has expressed the wish to use RJ-45. Otherwise I probably would have gone with DB25 a while ago. Thanks anyway for the suggestion

What I really need to know is if using unbalanced at line level is ok. If it is, I'll just use the Angry Audio pinout. If not, I'll have to figure out somwthing else or talk the guy into using a different connector...

Cheers
Sono

[has expressed the wish to use RJ-45] -- Well.....OK.....>> BUT!!! <<.....tell your buddy there.....that - IF - he is thinking of using the standard "El Cheapo" telephone-grade RJ-45 connectors, that they are going to end up in a world of hurt, pain and expense!!! WHY??? Because the standard "El Cheapo" telephone-grade RJ-45 connectors are just -- NOT -- robust and/or sturdy enough to survive the type of use that this headphone distribution system is probably going to encounter!!! THAT'S WHY!!! I used to work within the telephone industry long, long, long, long ago.....so I know how -- non-tough -- these connectors really are!!!

Once again....."Good Ol' NEUTRIK" has a set of "Heavy-Duty" RJ-45 connectors that have been designed specifically for the "Entertainment Industry" (i.e., concert sound-reinforcement and lighting systems) that ARE durable enough to withstand the typical abuse that such cables encounter daily. Here are some images of both the "male cable connector" and a "Right-Angle PCB-Mount" female connector:



"Right-Angle PCB-Mount" female connector:


[I really need to know is if using unbalanced at line level is ok] -- If by "Line-Level" you are talking about a signal-level of like -- +4dB -- then, yeah.....you will probably be OK. But, if you are talking about a "Consumer Equipment Line-Level" which is typically -- -10dBv -- then, yer heading fer trouble!!! Since you have mentioned that the audio signals will be coming from a mixer, I'm guessing you should be fine.

Now.....here's a topic that your buddy probably won't want to discuss, but it is absolutely necessary in order to determine not only which direction this projects heads-off to, but also how the entire system will be "physically designed", assembled and built!!! And, > YOU < will have to have this discussion with him!!!

And, the topic is.....MONEY!!! What kind of budget does this guy have to have all of these boxes, PCB's and cables designed and built??? You see.....if he is thinking of using telephone-grade RJ-45's, they're dirt cheap!!! But, they will fall apart and get bent-up in no time. However, using these NEUTRIK connectors is going to run some bucks [U.S.] (pounds [UK])!!! But, at least they will last for several years and years and years!!!

Then, there is the cost of having "GOD Knows" how many PCB's!!! Even if you are able to convince someone like myself to design the PCB's for -- FREE --, it's still gonna run some money to have a bunch of PCB's fabricated. THEN!!!.....who or how are you going to have the PCB's assembled??? YOU??? Or, have a PCB-assembly company do it for you?

AND, THEN!!!.....what about all of the boxes??? There's one of two basic ways this can be done. READY???

After everything has been all figured out and all of the parts have been determined, I can either:

1) Source and specify an enclosure by an enclosure vendor and download one of their 3D CAD-models of an appropriate type of an enclosure. Once I have it within my CAD-system, I can modify it to meet the mechanical needs of all of the connectors, LED's and switches for your design and send it back to the vendor. From there, they'll take my modified CAD-model file and have however many boxes that this system requires fabricated. Once everything has been fabricated, they will be shipped to you.

Or.....

2) Based upon the needs of this headphone distribution system, I could "design-from-scratch" a custom enclosure to meet all of the mechanical and PCB requirements and then send my CAD-file to a sheet-metal fabrication shop to have it made. Once fabricated, they will all be shipped over to you.

Your call!!!

While I have absolutely -- NO IDEA -- of what > ANY < of the costs will be for anything about this project, but if I was doing this for someone else and just as a "ballpark wild guess" of what this entire system MIGHT cost including all of the RJ-45 cables, connectors, PCB's, enclosures, switches, LED's and the WHOLE SHEBANG!!!.....I would tell the guy the whole thing >> MIGHT << cost around USD $1,000.00. That's just to be safe!!! This project could come in at around USD $500.00!!! WHO KNOWS??? The cost of 24 or 25 enclosures, plus the fabrication cost, is going to run into some good money just on its own!!! It's impossible to even guess right now at this point. But, I would at least let the guy know what -- he "might" -- need to spend and/or save up for!!!

>> Just a couple examples of possible enclosure types:



In any case.....this is my 2-cents worth (or, 2-pence or 2-shillings)!!!

/

 

[sonolink]

I just checked with my pal and he will be using a Zoom Livetrak 8 desk. This is a podcast mixer which has 3 independent mixes for headphones on TRS output connectors. He uses one for the original speaker and another one for the simultaneous translator. Those outputs look like common headphones outs, unbalanced stereo and have a gain/volume knob. My guess is that it should be ok to go unbalanced.

OR, I could convert those signals into mono and then balance them.......but maybe that'd be a bit overkill for this application, right?

Thanks for your time and help. I'll be back with a complete schem soon.
Cheers
Sono

 

[MidnightArrakis]

I just checked with my pal and he will be using a Zoom Livetrak 8 desk. This is a podcast mixer which has 3 independent mixes for headphones on TRS output connectors. He uses one for the original speaker and another one for the simultaneous translator. Those outputs look like common headphones outs, unbalanced stereo and have a gain/volume knob. My guess is that it should be ok to go unbalanced.

OR, I could convert those signals into mono and then balance them.......but maybe that'd be a bit overkill for this application, right?

Thanks for your time and help. I'll be back with a complete schem soon.
Cheers
Sono

[headphones on TRS output connectors] -- That would be a "Dual-Unbalanced / Small-Speaker Level" signal. I would need to know more about the ZOOM to make any suggestions right now.

[I could convert those signals into mono and then balance them] -- There is quite a bit of difference between the "Line-Level" output of a mixer and the "Headphones Out" signal.....as far as both signal-level and impedances and all of that. The impedance of a headphone usually ranges from 8-Ohms to 32-Ohms, while the mixer output is probably 600-Ohms or so. All of this kind of stuff is beyond my forte', so I would suggest that you discuss these things with "Ccaudle" and get all of that stuff worked out first.

NOTE: I was still working on my latest response even as you responded to it, so you may want to go back and re-read my last response. There is new information within it that you couldn't have seen when you read it the first time. Check it out!!!

/

 

[MidnightArrakis]

OUTPUT
MASTER OUT: Type: XLR jacks (balanced)
Maximum output level: +14.5 dBu
Output impedance: 100 Ω
MASTER OUT (PHONES): Type: Standard stereo phone jack
Maximum output level: 10 mW + 10 mW (60Ω load)
Output impedance: 10 Ω
MONITOR OUT (PHONES): Type: Standard stereo phone jack
Maximum output level: 10 mW + 10 mW (60Ω load)
Output impedance: 10 Ω

LiveTrak L-8 | Buy Now

zoomcorp.com

>> Where do the RJ-45 connectors come from???

/

 

[sonolink]

OUTPUT
MASTER OUT: Type: XLR jacks (balanced)
Maximum output level: +14.5 dBu
Output impedance: 100 Ω
MASTER OUT (PHONES): Type: Standard stereo phone jack
Maximum output level: 10 mW + 10 mW (60Ω load)
Output impedance: 10 Ω
MONITOR OUT (PHONES): Type: Standard stereo phone jack
Maximum output level: 10 mW + 10 mW (60Ω load)
Output impedance: 10 Ω

LiveTrak L-8 | Buy Now

zoomcorp.com

>> Where do the RJ-45 connectors come from???

/

If you take a peak at the diagram on my very first post you'll find out where they come from....

Cheers
Sono

 

[MicMaven]

IF - he is thinking of using the standard "El Cheapo" telephone-grade RJ-45 connectors, that they are going to end up in a world of hurt, pain and expense!!!

.if he is thinking of using telephone-grade RJ-45's, they're dirt cheap!!! But, they will fall apart and get bent-up in no time.

I agree.

Sidebar - amateur radio manufacturers sometimes terminate hand-microphone cables with RK-45 connectors - which is , as @MidnightArrakis says, a very foolish move. Whenever I encounter one, I immediately flood the connector with CA glue (superglue) to fuse the connector to the cable insulator. Even then, they fail at an alarming rate. Cheap for telephones, but surely contraindicated for any application with any degree of cable stress. Just my take. James

 

[MidnightArrakis]

Here are some other enclosure examples for you to review. These are aluminum enclosures:




With these enclosures, all that you need to do is come up with the H X W X D dimensions that you and your buddy want these boxes to be and then I can input them into a "Template Generator" on this enclosure vendor's website. Then and automatically, their website will create a "Template" CAD-file for me to download and then import into my SolidWorks 3D Mechanical CAD-modeling program. Once I have the file imported, then I can create all of the holes and cutouts for the various connectors, LED's, switches, etc. (NOTE: Which can only be done -- AFTER -- the PCB's have been designed!!!) and save the newly updated CAD-file of your enclosure in the SolidWorks file format.

Once I have that.....I can upload my SolidWorks file to the sheet-metal vendor's website and it will automatically provide me with a quote for fabrication. I'm going to use the quantity of 25 enclosures, OK?

You can also have the enclosure -- powder-coated -- in a number of colors (colours) and you can even have the TOP surface painted one color and the base section painted another color in order to make the enclosure look a bit more "dazzling"!!! In addition, instead of -- silkscreening -- the enclosure with the LED's, connectors and switches information.....the newest thing is to have the text (and, even a logo) "laser-printed" onto the metal-work and then what is called "white-filled" with epoxy-ink!!! LOOKS REALLY COOL!!!

RAL 7040 Window grey, 49/75470, Smooth Glossy, Polyester Powder
White Sandtex, PW-113-MT, Medium Gloss, Fine Texture, Polyester Powder
C031-WH120, White Texture Semi-Gloss, Polyester Powder
Storm White Sandtex, PW-206-LT, Low Gloss, Fine Texture, Polyester Powder
Black Sandtex, PB-134-LT, Low Gloss, Fine Texture, Polyester Powder
Fire Red, HR-105-H, High Gloss, Smooth, Hybrid Powder
Almond, PI-176-H, High Gloss, Smooth, Polyester Powder
ASA 61 Grey, PA-0183-G, Gloss, Smooth, Polyester Powder
Retro Grey, PA-388-M, Medium Gloss, Smooth, Polyester Powder
Graphite Sandtex, PA-191-LT, Low Gloss, Fine Texture, Polyester Powder
Aero Yellow, PFY601S9, High Gloss, Smooth, Polyester Powder
ANSI 70 Gray, 30-7065, Gloss, Smooth, Polyester Powder
Safety Orange, 39/20010, High Gloss, Smooth, Polyester Powder
RAL 6018 Yellow-Green, 49/52720, High Gloss, Smooth, Polyester Powder
RAL 5017 Traffic Blue, 49/40760, High Gloss, Smooth, Polyester Powder --- VERY ATTRACTIVE BLUE!!!
RAL 6002 Leaf Green, 149/52890, High Gloss, Smooth, Polyester Powder
RAL 6003 Olive Green, 49/52880, High Gloss, Smooth, Polyester Powder
Federal Standard 595 Color FS 37038 Flat Black, E300-BK11, Flat, Smooth, Epoxy Powder
RAL 3005 Wine Red, Smooth Glossy, Polyester Powder
RAL 3020, Traffic Red, Glossy Polyester Powder --- ATTENTION-GETTING GREAT RED COLOR!!!
RAL 1003 Signal Yellow, Smooth Glossy, Polyester Powder
RAL 9005 Jet Black, H302-BK46, Smooth, Hybrid Powder
RAL 5010 Gentian Blue, PL-0725-LT, Low Gloss, Sandtex, Polyester-Epoxy Blend (Hybrid)
Federal Standard 595 Color FS 26307 Gray, P003-GR01, Semi Gloss, Smooth, Polyester Polyurethane
RAL 7035 Light Gray, PA-1083-LT, Low Gloss, Sandtex, Polyester Powder
RAL 3002 Carmine Red, HR-0287-LT, Low Gloss, Sandtex, Hybrid Powder
Resicoat® EL HGD47QF ECA-1283 Red 3332
RAL 9003 Signal White
Resicoat® EL HNF35QF ECB-1363A Black 2701
C241-GR484 Polyester Semi Gloss Texture, Dark Gray ( 50 lbs )
Federal Standard 595 Color FS 17038 Black, T009-BK12, Full Gloss, Smooth, Polyester Powder
Wheat , JD311QF, Low Gloss, Sandtex, Polyester Powder
Federal Standard 595 Color FS 33446 Desert Tan, P000-BG631, Smooth, Flat, Polyester Powder
Matte Black, 409/80360, Low Gloss, Smooth, Hybrid Powder




I was thinking of the TOP COVER being the -- TRAFFIC BLUE -- color and the BASE UNIT being the -- TRAFFIC RED -- color, both having any text information "laser-printed & white-filled" would look GREAT!!!

>> IT'S TIME TO START FIGURING OUT HOW YOU GUYS WANT THIS "HEADPHONE DISTRIBUTION SYSTEM" TO BE!!! <<

/

 

[sonolink]

Sorry if this is a dumb question, but if I'm using a preamp after the A/B switch on each channel (represented by "Volume Knob" on the pic), do I really need a buffer before that?

Thanks
Sono

 

[MidnightArrakis]

If you take a peak at the diagram on my very first post you'll find out where they come from....

Cheers
Sono

[on my very first post you'll find out where they come from] -- GOT IT!!!

> How do the enclosures look to you in my Post #48?

> Question: Is there a particular reason on -- why -- your block diagram drawing is drawn "Right-To-Left" instead of "Left-To-Right"? I'm just wondering why.....that's all.

> A Thought: I'm not any kind of a "Circuit-Design" person at all, but it would seem to me that if your "BUFFER" circuit was placed -- before -- the "A/B Switch", then the overall load impedance could be maintained across the entire system and the "A/B Switch" would then be merely selecting which one to monitor. Something like this (only showing one set of A/B signals):


THOUGHTS??? NOTE: The RJ-45 pinouts and such may not be "technically correct", but this drawing is purely just to convey an idea and -- NOT -- be "electrically or schematically correct"!!!

While I am assuming that the "B Box" will probably be placed onto a desk that will have people sitting there at it, where will the "A Box" be placed? Next to the ZOOM? In a rack? Suspended from the ceiling using rare Tibetan yarn? > WHERE < will determine what type of enclosure to best use!!!
/

 

[MicMaven]

where will the "A Box" be placed? Next to the ZOOM? In a rack? Suspended from the ceiling using rare Tibetan yarn?

Hmmm ... maybe a hand-knitted craft art macrame sling like what was popular in the early 1970s. JHR?

 

[MidnightArrakis]

Sorry if this is a dumb question, but if I'm using a preamp after the A/B switch on each channel (represented by "Volume Knob" on the pic), do I really need a buffer before that?

Thanks
Sono

View attachment 117262

Here's a possible "idea" of what your PCB "might" look like:



>> The capacitors and resistors are -- actual -- sized components based upon a "Headphone Amplifier" schematic I found online using an NE5532 as the driver IC. This means you would have a pair of NE5532's used as your -- BUFFER -- and another pair of NE5532's for your "Headphone Amplifier". The white "MOLEX" connectors that you see are for connecting the two stereo "VOLUME" pots to the PCB, as they will probably be mounted onto the enclosure top-panel some distance away from the PCB itself. Of course, any of this is subject to change.

NOTE: While I do realize that you have been looking for "pre-made" headphone amplifiers, the main problem I see with using such a device is that it is -- a separate item -- that needs to be mounted somehow, as well as wired-up to. However, if you just use a "headphone amplifier circuit" (whatever circuit that you would choose to use), then it can be easily integrated into a PCB along with the "BUFFER" circuitry. The "BUFFER" circuitry would be place immediately behind where you see the two NEUTRIK RJ45 connectors. I "might" add that circuitry into this PCB sometime later. But, for now.....this should give you a pretty good idea of how things "COULD" go. Any comments?

And.....just for "kicks".....the color-codes that you see on the resistors are the -- ACTUAL -- color-codes used for the various values used in the schematic that I got the circuit from!!! ISN'T THAT FUN???




ARE WE HAVING FUN YET???

/

 

[sonolink]

> How do the enclosures look to you in my Post #48?

I was thinking something like a Hammond 1590B o a 1590BB.

> Question: Is there a particular reason on -- why -- your block diagram drawing is drawn "Right-To-Left" instead of "Left-To-Right"? I'm just wondering why.....that's all.

No particular reason

> A Thought: I'm not any kind of a "Circuit-Design" person at all, but it would seem to me that if your "BUFFER" circuit was placed -- before -- the "A/B Switch", then the overall load impedance could be maintained across the entire system and the "A/B Switch" would then be merely selecting which one to monitor.

I thought it wouldn't matter if it was placed before or after the switch, so I went for the cheaper solution that requires only one buffer per channel.

While I am assuming that the "B Box" will probably be placed onto a desk that will have people sitting there at it, where will the "A Box" be placed? Next to the ZOOM? In a rack? Suspended from the ceiling using rare Tibetan yarn? > WHERE < will determine what type of enclosure to best use!!!
/

I don't think it really matters does it? I mean probably next to the first B-Box in the chain or next to the mixer...I was thinking of using the same kind of enclosure as the B-Boxes.

 

[sonolink]

Can someone please tell me if a buffer is really needed since I'm using a preamp right after on each channel? Wouldn't the preamp serve that function?

Cheers
Sono

 

[MidnightArrakis]

I was thinking something like a Hammond 1590B o a 1590BB.



No particular reason




I thought it wouldn't matter if it was placed before or after the switch, so I went for the cheaper solution that requires only one buffer per channel.




I don't think it really matters does it? I mean probably next to the first B-Box in the chain or next to the mixer...I was thinking of using the same kind of enclosure as the B-Boxes.

[I was thinking something like a Hammond 1590B o a 1590BB] -- How about the HAMMOND 1591 Series of enclosures -- BECAUSE --.....they also have built-in PCB-standoffs!!! Otherwise, with using the 1590's, you're going to need to first have four holes drilled and an additional 4 separate standoff pieces plus an additional "4 standoff mounting screws -- MULTIPLIED BY -- the total number of boxes"!!! An enclosure like this 1591 will save your project a whole lot of assembly labor and time when these are being put together. Just sayin'.....



One thing I have happened to notice about the HAMMOND enclosures, whether they're the die-cast ones or the plastic ones, is that they -- ALL -- have what is called a "draft angle" on their sides. Now, while this may not end up being a "BIG DEAL", what the "draft angle" does is that it prevents any of the parts that are mounted to a PCB that protrudes -- through -- the side from being completely "flush" with the side. Maybe it won't matter, I don't know yet. (Look at the image below over on the right-side where it says "BOX HEIGHT". You will see that the side has an angle or a "tilt" to it):



Here's a drawing of a "1590" enclosure and you can see the same thing here:



Another item you should keep in mind is that despite whatever enclosure you end-up deciding to use, you will also need some -- RUBBER MOUNTING FEET -- applied to the bottom of the enclosure to prevent it from moving around on the desk or table that these boxes will be placed upon. Otherwise, even a gentle tug from either the RJ-45 cables or the headphone cords that are plugged into these boxes will cause them to move around and/or possibly even be pulled-off the desk or table. Just a thought, ya know???.....

[where will the "A Box" be placed? (probably next to the first B-Box in the chain or next to the mixer)] -- If that's the case.....then it "makes sense" (and, probably only to "me"!!!) to have instead a "Master Box" that would combine both the "A" box and "B" box functions together. This would also then provide the person at the mixer with a type of "MONITOR" function, allowing them to hear the exact same thing as all of the users are hearing along with the same type of switching capability. Again, this is just me.

Ideas??? Suggestions??? Thoughts???

/

 

[sonolink]

I really appreciate all your ideas, enthousiasm and input Jerry, but now what I really need to know is if I really need a buffer before the preamp or I can do without it if the preamp acts as a buffer itself, since that will change drastically the PCB design and cost.

Thanks for your time and help
Cheers
Sono

 

[MidnightArrakis]

I really appreciate all your ideas, enthousiasm and input Jerry, but now what I really need to know is if I really need a buffer before the preamp or I can do without it if the preamp acts as a buffer itself, since that will change drastically the PCB design and cost.

Thanks for your time and help
Cheers
Sono

[if I really need a buffer before the preamp] -- If you are referring to the diagram below, I would have to say "YES"!!! But, that's just me. That is a question you would be better off asking your buddy "Ccaudle":



I am saying that "YES!!!" you would need a buffer because the buffer circuitry can be configured to not only -- isolate -- the "Headphone Amplifier" (is this what you are calling the "preamp"?) from the rest of the system, but it can also be configured to provide both a consistent and optimum impedance load, whether you have a single "B-Box" connected or 24 "B-Boxes" connected and a consistent drive-signal to the "Headphone Amplifier". Again.....I am -- NOT -- a "Circuit Designer" person, but from what I have seen in other "distribution" systems, using a buffer in a position as in the above diagram is typical. Someone like "Ccaudle" could probably design an easy buffer circuit for you.

And, as if it even matters to you.....if >> I << were designing and building a system like this? I would most definitely place a buffer circuit as shown in the above diagram. But.....that's just me. Ccaudle just might tell you that "I'm crazy stupid!!!" and you don't need a buffer whatsoever!!! But, my gut tells me that your distribution system will more than likely perform much better if the system did use some buffers. It's "kind of like" (only different) in a mixing console where you have an "AUX" signal feeding all of the channel-faders.....there is an "Input Buffer" on each channel, performing the same manner of functions as detailed earlier.

[if the preamp acts as a buffer itself] -- While the preamp (Headphone Amplifier?) does "kind of" act as a buffer, it's not in the same way. Should there be only 6 "B" boxes connected, that will present one type of load to the "A" box and ultimately to the "6.35mm Stereo Phone Connection" and wherever that signal is coming from. Then, if there are 20 "B" boxes connected, that will present an entirely different impedance load to the system and, of course, to the "6.35 Stereo Phone Connection".....which will then probably cause the signal-level to shift.

By using a buffer, it can be configured to offer a more consistent impedance load to the entire system regardless of the number of "B" boxes connected, in addition to also maintaining a consistent signal-level.

But, then again.....I could be full of shit!!! Ask "Ccaudle" or someone similar.

/

 

[sonolink]

I have the impression you're right. I just wanted to be sure to avoid putting something redundant in the system. Thanks a lot for your time and help Jerry

BTW, I like your idea of combining both the "A" box and "B" box functions together in a "Master Box".

Cheers
Sono

 

[Hubbub]

It would help if you drop back to basic electronics. Unless I missed something in the last 60 years impedance matching is critical in only two situations: 1) power transfer must be maximized, 2) cable length is such that reflections can occur. For audio case 1 is almost never a concern, although it might be in specialized situations. Headphone powering is not one of those situations. For case 2 reflections start to be a concern if the cable approaches 1/10 wavelength of the highest frequency. At 20KHz the wavelength in a vacuum (I know... but this is for simplification) is 15000 meters. One tenth of that is 1500 meters, or almost 5000 feet. Are you using the furthest "B" box at about 5000 feet from box "A"? If "NO" then case 2 doesn't apply and forget about impedance matching.

That said, impedance is important. You want a low enough source impedance that you can provide a good signal down the bus for the maximum number of connected loads. You want a high enough load impedance that connecting or disconnecting any one (or number of, you pick) load(s) has negligible effect on the signal level of the bus. For example, let's say the source output impedance was 10 Ohms, the load input impedance was 100K Ohms, and you had a 1V RMS signal from the source with no load. Connect anywhere from 1 to 100 loads and the input never drops below 0.990V, a drop of 0.086dB. That is so little that no one will notice switching on (or off) 100 loads!

As to whether you need a buffer, it all depends on the impedances you are dealing with, and how many loads you expect to have. Design the system right and the correct answer is NO, or maybe YES. It's all in the tradeoffs. You need to understand the basics well before you can intelligently manage the tradeoffs.

 

[Voyager10]

A bigger worry might be power distribution, depending on how loud the amps need to be, and what headphones they're driving.

Cat 5 cable (according to Category 5 cable - Wikipedia) has a resistance (for a pair of conductors forming a loop) of 0.188 ohm / metre, so a 100m length will be 18.8 ohms (plus all the contact resistance and wiring resistance in each box).

If you allow for 1V supply voltage drop over the length of the cable, you get ~ 50mA total. That's not a huge number of headphone amps (something cheap & cheerful like the TDA2822 - https://www.st.com/en/audio-ics/tda2822d.html - draws 15mA with no signal).

Some things to consider might be:
- a 'star' topology with several shorter connections out from the 'master' box, rather than a single long daisy-chain
- a higher DC supply voltage (24-48V) with switching converters / regulators to power the amps
- use fancier headphone amps (e.g. class D) which don't use so much power
- use high-impedance headphones (200-600 ohms) which use higher drive voltages but lower current


(PS: "100V line" is still alive and kicking: just a big power amplifier at the start and audio step-down transformers in each box, see e.g. https://audiovolt.co.uk/blogs/av-insight-background-audio-advise/guide-to-100v-line-audio-systems. Totally passive, and largely immune to interference)