HELP with designing a headphones distributor please

[sonolink]

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.

I just read the datasheet and you're right. I bet someone dropped a decimal ))

I think I'll go with the PAM then. Thanks a lot for pointing that out!
Cheers
Sono

 

[sonolink]

A couple of questions about buffering please: if I want to chain several B Boxes (let's say 20), I probably need a buffer between each box.

Where should I place the buffer?
-after the input RJ45
-just before the output RJ45?
-does it actually matter?







Thanks a lot for your time and help
Cheers
Sono

 

[ccaudle]

Where should I place the buffer?

If the buffer input impedance is high enough you can put the buffers in front of the A/B switches, and just let the audio run through the B boxes.

 

[sonolink]

If the buffer input impedance is high enough you can put the buffers in front of the A/B switches, and just let the audio run through the B boxes.

Thanks for your quick reply

I could use this buffer in front of each switch for instance?

 

[ccaudle]

I could use this buffer in front of each switch for instance?

Yes, something like that (if still using unbalanced inputs). Doubled up if you are using balanced inputs (your original description was just unbalanced input but I wasn't sure if you were considering changing to balanced line level input like suggested in post #10).

 

[sonolink]

Actually that's an important point I have overlooked!

I have to check what the source will be. The purpose of this thing is a headphone distribution system to be used for simultaneous translation. So, channel A would be the original audio and channel B the translated version. I have to check with the person that has asked me to build it, where the source audio will be coming from (i.e. a mixer output). If the source is balanced line level I'll definitely need to maintain that. I also have the feeling that if the source is unbalanced it's convenient to balance it to avoid noise, isn't that so?

Thanks a lot for your help
Cheers
Sono

 

[sonolink]

Yes, something like that (if still using unbalanced inputs). Doubled up if you are using balanced inputs (your original description was just unbalanced input but I wasn't sure if you were considering changing to balanced line level input like suggested in post #10).

I just checked and the source will be a mixer output, so I definitely have to go balanced line level
And I will definitely go with the Angry Audio pinout.

Thanks for pointing that out ccaudle!
Cheers
Sono

 

[sonolink]

Would this buffer work?



And would it be ok to use it AFTER the switch like so?



Cheers
Sono

 

[sonolink]

I just realized I can't go with the Angry Audio pinout. I need to send TWO stereo signals + Power for each B Box. If using unbalanced I could go as Hubbub suggested

1- chA L
2- chA R
3- V+
4- Audio GND
5- Power GND
6- V-
7- chB L
8- chB R
9- shield to GND

But if I would want to go Balanced I don't have enough pairs. Maybe Thomas' idea of superposing power over audio?

1- chA L+ / V+
2- chA L- / V+
3- chA R+ / V+
4- chB L+ / V+
5- chB L- / V-
6- chA R- / V-
7- chB R+ / V-
8- chB R- / V-
9- shield to GND

The source is going to be a balanced signal from a mixer out.
Opinions? Thanks

Cheers
Sono

 

[ccaudle]

superposing power over audio?

The only problem I can see there is that there is an indeterminate number of loads, which makes the scheme used for phantom powering microphones difficult, since your current draw will vary proportionally with the number of B boxes you have.

 

[sonolink]

I'm afraid there's a misunderstanding. I'm sorry for the language barrier. There are no microphones involved whatsoever. The power should serve only to feed the headphone amps and buffers. Source signals in channels A and B are coming from a mixer.

Should I go unbalanced then?

 

[ccaudle]

There are no microphones involved whatsoever.

Understood, I was just making a reference to the way power is provided for microphone with balanced audio wiring, power supplied to the wires through resistors.
I am not sure how else you would implement what you show in post #33 where one channel of balanced audio also has power on the wires. You either have to supply power through two resistors, or through the center tap of a transformer. The voltage drop across the resistors is proportional to the current, so more voltage drop every time you add another B box to the chain.

 

[sonolink]

Thanks for your input ccaudle

2 questions come up in my mind now:

1- if going balanced and wiring the power boxes in parallel, I wouldn't have any voltage drop, right? I'm not sure that would be possible since audio and power would be sharing wires but just out of curiosity.

2- the important question: the source is going to be line level. Is it THAT bad to go unbalanced?
Boxes will be a couple of meters away one from each other max...Cat cables will be shielded and grounded, and the boxes will be made of aluminium...

What do you reckon?
Thanks A LOT for all your ideas
Cheers
Sono

 

[sonolink]

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

 

[ccaudle]

if going balanced and wiring the power boxes in parallel, I wouldn't have any voltage drop, right?

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.

Is it THAT bad to go unbalanced?

Probably not. You don't have separate AC power connections to each box, which is a big part of where noise is introduced in most unbalanced equipment.
It is also just for monitoring, so in cases where you do get a little bit of interference it is not ruining the recording.

 

[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

 

[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

 

[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

https://zoomcorp.com/en/us/digital-mixer-multi-track-recorders/digital-mixer-recorder/LIVETRAK-L-8/
>> 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

 

[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