HELP with designing a headphones distributor please

[sonolink]

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.



Any help would be most appreciated. Thanks in advance for your time and help

 

[totoxraymond]

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

 

[sonolink]

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

 

[ccaudle]

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

 

[totoxraymond]

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

 

[sonolink]

Thanks a lot to both for all the info. I'll do some reading and get back.
Cheers!!
Sono

 

[sonolink]

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

 

[MidnightArrakis]

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

While I am more than certain that there will be many others here who will fervently disagree with me on this, personally.....I would put the "Power" connections on the two outer pins (1 & 8) and the GND on Pin-5. My reasoning is to keep the power connections and GND away from one another should some pins in a connector become bent-up and possibly touch one another. Then, within your power-supply circuitry, you could place some "protection" diodes in there to try and help protect anything else from shorting out.

Just a thought.....

/

 

[Hubbub]

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.)

 

[AngryAudio]

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

 

[totoxraymond]

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

 

[sonolink]

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

 

[sonolink]

Do you reckon I can use 2 of these for each box B? They are really cheap...

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es.aliexpress.com

Thanks!
Sono

 

[sonolink]

Nobody?

 

[totoxraymond]

I really din't know about this product.

Given the price, you might try it and see if it works for you.

Thomas

 

[MidnightArrakis]

Do you reckon I can use 2 of these for each box B? They are really cheap...

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es.aliexpress.com

Thanks!
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'.....

/

 

[sonolink]

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/1005002813276608.html?spm=a2g0o.detail.0.0.3082eAKfeAKfse&gps-id=pcDetailTopMoreOtherSeller&scm=1007.40000.327270.0&scm_id=1007.40000.327270.0&scm-url=1007.40000.327270.0&pvid=9bebc9ac-756c-4ebd-97af-41731fd55e38&_t=gps-id:pcDetailTopMoreOtherSeller,scm-url:1007.40000.327270.0,pvid:9bebc9ac-756c-4ebd-97af-41731fd55e38,tpp_buckets:668%232846%238109%231935&pdp_npi=4%40dis%21EUR%211.17%210.78%21%21%211.23%21%21%402103893b16992885783346922eea60%2112000022314806416%21rec%21ES%21%21AB&search_p4p_id=202311060836183732837386678597670131_1

Or this one?

https://es.aliexpress.com/item/4000019719055.html?src=google&src=google&albch=shopping&acnt=439-079-4345&slnk=&plac=&mtctp=&albbt=Google_7_shopping&albagn=888888&isSmbAutoCall=false&needSmbHouyi=false&albcp=18928172568&albag=&trgt=&crea=es4000019719055&netw=x&device=c&albpg=&albpd=es4000019719055&gad_source=1&gclid=EAIaIQobChMI7PakleevggMVzJ5oCR0ZSwKtEAQYEiABEgJrN_D_BwE&gclsrc=aw.ds&aff_fcid=76e70e6f7d654e538e3f1fb611978fe2-1699288641915-03304-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=76e70e6f7d654e538e3f1fb611978fe2-1699288641915-03304-UneMJZVf&terminal_id=c04121ffc92f4a7381396123bf95e9c0&afSmartRedirect=y

Thanks for all your input

 

[MidnightArrakis]

[1) Do you reckon I can use 2 of these for each box? 2) Are you sure it's not stereo? The "OUT" pins are labelled "L", "R" and "G" ] -- My BAD!!!.....I guess. Since you had mentioned you wanted to "use 2" of these PCB's and I didn't look that closely at the spec's of the PCB headphone amplifier, I (wrongly) assumed that it was a -- mono -- unit and you were using 2 of them for "stereo". OK.....so I blew it!!!

In any case, it's still only 80mW.

Between the other 2 newer selections of yours.....I tend to favor the TDA2822 device over the PAM8403, primarily because it can use a 12VDC power-supply (which means lower current draw) and that it also comes with a knob on the pot. Small detail, I know, but.....it saves you from having to also buy a bunch of knobs!!!

However, one item that bothers me about both of these other selections of yours is.....while they both sport having a few watts of output, they are claiming to do so -- WITHOUT -- using any type of a heatsink!!! So, in assuming that what is being claimed is "true", this means that under continued long periods of use, the IC's could get toasty enough during a session to finally burn-out!!! I could be wrong about this, but running a tiny IC chip at its full-power for an extended amount of time while its rather toasty is eventually going to lead to a failure.

Now.....you can get some IC chip heatsinks and stick them on there with some "thermal grease" (real stuff!!!) and that might be OK, but if I were doing things in the manner you are taking, I would find a headphone amplifier PCB that at least has a TO-220 type of transistor heatsink on it. If a headphone amplifier PCB at least had a TO-220 heatsink on it, then I would feel a bit safer about running it "full-hog" on its output. Either that, or find a headphone amplifier schematic that you like and build it yourself.

>> PCB-MOUNTED -- TO-220 HEATSINK with THERMAL PAD & MOUNTING SCREW


>> THERMAL PASTE

I am more than certain that there are a bunch of headphone amplifier schematics available on the GroupDIY forum website if you do a search on it.

/

 

[ccaudle]

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.

 

[sonolink]

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?