HELP with designing a headphones distributor please

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sonolink

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Joined
Feb 15, 2010
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Hello everybody,

Can someone please help me with the following circuit please? I've made a diagram. I was wondering if anyone knows some ready made circuits I could use and what sort of amplifier and if RJ45 can be used for this. I'm a bit lost with the technical requirement TBH....
So basically, Box A "converts" both stereo channels A and B from 6.3mm jack to Rj45. Box B is a 2 stereo channels active amplifier for headphones.
It receives channels A and B through an RJ45, sends a "through line" towards the next RJ45 and taps signal from both channels to each switch so that each user can choose which channel to listen to and at what level. The idea is to chain several B Boxes.

CajasA-B-1 a.jpg

Any help would be most appreciated. Thanks in advance for your time and help
 
I made a box like this. Each phone output has its own amp and can choose between 4 stereo inputs.

I used db25 instead of rj45 as connectors but i think you can use rj45 to transmit analog signals as long as you use cat5/6 shielded cables.

My design didn't include a buffer between input and "link" but that's because i only intended to use 2 boxes max. (Only made one in the end).

But your box B should need power while box a can be passive. Unless you intended to use some PoE, in this case i don't know if it is possible.


Thomas
 
I made a box like this. Each phone output has its own amp and can choose between 4 stereo inputs.

I used db25 instead of rj45 as connectors but i think you can use rj45 to transmit analog signals as long as you use cat5/6 shielded cables.

My design didn't include a buffer between input and "link" but that's because i only intended to use 2 boxes max. (Only made one in the end).

But your box B should need power while box a can be passive. Unless you intended to use some PoE, in this case i don't know if it is possible.


Thomas

Hello Thomas,
Thanks a lot for your input :)
What amp did you use for the phone outs? My idea was to use PoE fed from Box A indeed. I need to know what is the max juice Cat8 and RJ45 can handle. Would you mind sharing your design or the amp schem please? :)
Cheers
Sono
 
as long as you use cat5/6 shielded cables.

You don't absolutely need shielded cables if you are willing to filter the audio relatively aggressively. Not aggressive in the sense of damaging the audio necessarily, just being really fastidious about RF filter layout. Shielded cables would make that less important, you would just be a little more limited in being able to grab any random Ethernet cable for link.

My idea was to use PoE fed from Box A indeed

Be aware that PoE used to mean IEEE standards PoE techniques take advantage of the fact that Ethernet is transformer coupled and put the power as common mode voltage on the signal pairs.
Actually, now that I review there is a standard which uses two pairs for data, and two different pairs for power, so that might work without having to worry about the common mode voltage on the audio lines. You would have to be very careful that your PoE power supply was only a type B 802.3-af supply.
Wikipedia has a good overview of PoE.

what sort of amplifier

There was a rather exhaustive (exhausting?) thread recently which covered everything you would need to know about headphone amplifiers, everything from "just use an op-amp" to multi-op-amp designs for increased current output to discrete transistor current boosters:
Headphone amp thread
 
I know at least one commercial design using PoE for 4 headphones output, so available power should be sufficient. But that is a Dante headphone amp, no analog input.

I attached a schematic of my amp. Actually, it's a newer version with switching and amp on one PCB which i haven't tested yet, so I hope there's no mistake there.
The actual amp part, is not my design. I think it was Jakob or Igor (can't remember honestly) who designed it.
The switching part is very simple, but it works quite well, and uses only one switch to select between 4 inputs.
Note, that it uses a dual supply, so i don't think it could be used with PoE.
Schematic doesn't show PSU or line receivers because I made them on separate boards.

Cheers,

Thomas
 

Attachments

  • HP_Amp_PCB.pdf
    130.2 KB · Views: 5
Ok so I've been reading those links and that thread and my head is smoking:)
There's a lot of info I cannot process because I'm an ignorant hobbyist really, but I love learning and will try my best with my homework if O can have a few directions from here :)

I think the simplest would be to buy ready made circuits or kits for the headphones amps. I need to figure out what else I need in each box and how to connect it.

So, beginning with the RJ45 pinout (sorry if this is a dumb question) would this work?

1-ch1 L
2-ch1 R
3-ch2 L
4-ch2 R
5-Audio GND (common to ch1 and ch2)
6-Power + voltage
7-Power - voltage
8-Power GND (0v)

Cheers
Sono
 
Also keep in mind the common RJ-45/Cat5e/Ethernet pairing per TIA T568A/B. Cable pairs are 1-2 4-5 7-8 and 3-6. Assign signals to pins/pairs in a way that make sense for crosstalk to not be so much an issue. I'd choose 1-2 for A L&R, 7-8 for B L&R, 4-5 for the grounds, and 3-6 for +V and -V. (This assignment is not necessarily what another engineer would choose, YMMV.)
 
Suggest you use the StudioHub+ pinout. There are many devices that already use this pinout. It's a defacto standard in broadcasting. It's very similar to what you are thinking so why not have the benefit of compatibility with other devices?

Pin1 Left Hot
Pin 2 Left Cold
Pin 3 Right Hot
Pin 4 Ground for power supply (if used)
Pin 5 No connection
Pin 6 Right Cold
Pin 7 -15VDC (if used)
Pin 8 +15VDC (if used)

Most devices do not use the power pins. In those cases, no connection to those pins on the device. More info at studiohub.com
 
Why not use the 8 pairs to send analog balanced audio. And superpose dc voltage over it, very much like a phantom power.

You could use half the conductors to carry +v and the other half tl carry -v, use the shield as dc return path.

This would make the use of shielded cables mandatory. But would make your system more resistant to interferences. and also allow you to carry more current. As well as gumive the ability to connect to a commercial breakout box should you ever need it.

I didn't research the ieee PoE norm, but you might also try to comply with it although i guess it would mean to restrict to single supply. (So a different design for the headamp)


Lots of options to consider...

Thomas
 
Wow guys, thanks a lot for all the input! Plenty to chew on for a bit and really LOTS of options indeed.

Thanks again for all the info
Cheers
Sono
 
You couldn't even buy all of the individual parts for what this single PCB costs!!! However, one of the downsides is that you would end up with a "dual-mono" headphone system and NOT a "stereo" system, meaning that the end-user/musician would have to rotate two individual pots in order to have an equal volume in their ears instead of a single 2-channel pot. That could possibly be too much of a hassle for a musician to deal with during a session. Just a thought.....

Also, this little "headphone amplifier" only has 80mW output, which is less than 1/10th-Watt and that may not be enough to adequately drive the headphones to an acceptable user level during a session, especially during a rock/heavy-metal session!!! I am fairly certain you can find similar headphone PCB's that are in the 1-to-5 Watt range which would easily provide enough OOMPH!!! to drive your headphones during a session.

And.....I would also look for a 2-channel or "stereo" amplifier, unless you already have your headphones wired for mono. Just sayin'.....

/


Are you sure it's not stereo? The "OUT" pins are labelled "L", "R" and "G"....


Or how about this one then?

https://es.aliexpress.com/item/1005...p4p_id=202311060836183732837386678597670131_1
Or this one?

https://es.aliexpress.com/item/4000...1ffc92f4a7381396123bf95e9c0&afSmartRedirect=y

Thanks for all your input :)
 
WITHOUT -- using any type of a heatsink
The PAM device is class D, it should not have much dissipation.
The TDA device is class AB, and the package is only rated for 1W, so I think you would need to do your own homework there and not rely on the design being done right from the unknown super cheap vendor.
 
The TDA device is class AB, and the package is only rated for 1W, so I think you would need to do your own homework there and not rely on the design being done right from the unknown super cheap vendor.

Doesn't the vendor state that the TDA device power rating is between 0.1 and 5w?
 
I'm not even sure what the OP is fully attempting to achieve especially since there are entire "headphone distribution systems" that can be purchased for studio use. I'm just trying to help the guy out without getting too involved in a bunch of details about it (you would need to do your own homework). While I do kind of understand somewhat what it is that he is attempting to accomplish, if it were me trying to do the same thing..... I would be taking an entirely different approach.

I'm outta here!!!

C'YA!!!


/

I apologize if my first post didn't express clearly what I was trying to attempt. MY idea of posting on this forum for years always has been learning and receiving ideas and suggestions (and of course help when I'm lost).

My post said:

"Hello everybody,

Can someone please help me with the following circuit please? I've made a diagram. I was wondering if anyone knows some ready made circuits I could use and what sort of amplifier and if RJ45 can be used for this. I'm a bit lost with the technical requirement TBH....

So basically, Box A "converts" both stereo channels A and B from 6.3mm jack to Rj45. Box B is a 2 stereo channels active amplifier for headphones.
It receives channels A and B through an RJ45, sends a "through line" towards the next RJ45 and taps signal from both channels to each switch so that each user can choose which channel to listen to and at what level. The idea is to chain several B Boxes.
"

After some kind people cleared out that RJ45 can be used and provided me with quite a bit of info to read, and while reading it I tried to figure out what ready made circuits I could use. Not that I don't want to build, but considering the price of some of those circuits and that I would need quite a few of those B boxes I just thought of keeping things simple.

Anyway, thanks for your input
Cheers
Sono
 
Doesn't the vendor state that the TDA device power rating is between 0.1 and 5w?

Indeed it does state that on the Aliexpress page.
You can get the datasheet for TDA2822 and take a look at the device limits for yourself. I do not see that the device vendor makes that claim, and taking a quick look at the datasheet I do not see that anything close to 5W is feasible. Like I said, you need to do your own homework, I do not consider aliexpress a reliable source of technical information.
https://www.st.com/en/audio-ics/tda2822d.html
It appears that ST is willing to claim the device is good for about 0.5W, but with some caveats around supply voltage vs. headphone impedance. Presumably that is to keep the device dissipation within acceptable limits, you have to reduce the power supply voltage if you want to drive low impedance headphones.
So either someone dropped a decimal point along the way, and 0.5W became 5W in the board description page, or someone just copied and pasted information not completely relevant to this design.
 
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