HELP with designing a headphones distributor please

[Voyager10]

Does this schematic make sense to anyone here??? This is based upon how I have sleep-deprived understand the latest changes, suggestions and updates to this project. ..... Let me (and, Sonolink) know, OK??? View attachment 117712 /

The volume pots seem to have disappeared, but that's going to be obvious after a good night's rest ;-)

 

[ccaudle]

I just bought these

Do you have a way to measure those transformers? That picture looks suspiciously like this Amazon product link, which has several comments from customers indicating they measured the transformers and the turns ratio is not anywhere close to what is claimed in the description:
transformer at U.S. Amazon

I'm not sure if Amazon will let you easily go to that link or not, it may try to redirect you to a .uk page which does not have the same product links.
I just found that by searching for "1300:8 EE14 transformer" that matched the description you showed.

The product description at Amazon is "10pcs 1300 : 8 Ohm Audio Transformer EE14 Transformateur POS Transformador for Voltage Amplification and Power Output" from YWBL-WH Store if that helps find the equivalent on the local site.

Anyway, the only point is the parts don't seem to be from a well known components manufacturer, so take the technical claims with some skepticism until you can verify the performance.

 

[Hubbub]

[The volume pots seem to have disappeared] -- No.....they were actually there, but they were testing out their new "Romulan Pot-Cloaking Technology" and it apparently worked!!! I forced them both to turn-off this new technology later on this morning and now you can clearly see them. Interesting stuff!!!.....

[that's going to be obvious after a good night's rest] -- It wasn't until just mere moments after I had pulled my bed covers up over my head earlier this morning that I had a thought of adding what my CAD-system calls a "Net Alias" to all of the connections in order to make it easier to visually follow what the Net Names are and where they all go. Hopefully, this addition will make Sonolink's schematic somewhat easier to read and follow along with.

Does this version of this schematic NOW make sense? Bueller? Bueller?? Bueller???.....
View attachment 117728
/

Yes it makes sense, but I wouldn't use it - because of the junctions. The junctions turn each segment of cable into two shorted loops with some open space (one pair to another) between them. Shorted loops like that are great receivers for magnetic fields, converting the field to a nice high current and consequent voltage drop. Think HUMMMMM. That's why I prefer the version without the junctions. Just following the "keep your loops tight" rule of noise immunity.

While we are at it it might be good to break up the long cable run with series ferrite beads, one per line, between input and output connectors. Probably best placed tight at the input connector but, since either connector could be an input, maybe at both connectors - 16 ferrite beads in all.

 

[ccaudle]

my experience with shielded RJ-45s is that they usually have two shield pins

One thing I don't think anyone has brought up yet is that with the change to speaker level instead of line level connection, there isn't really a need to use shielded cable any longer. In fact the extra capacitance of shielded cable might be difficult for the amplifier to drive, so in addition to being cheaper it might avoid oscillations from the cheap amplifier driving 10m of cable.

 

[sonolink]

Do you have a way to measure those transformers? That picture looks suspiciously like this Amazon product link, which has several comments from customers indicating they measured the transformers and the turns ratio is not anywhere close to what is claimed in the description:
transformer at U.S. Amazon

If I can measure them with a multimeter I'll check them out. In any case, I hjave seen several sellers that sell those and the one I bought from has the best rating.
Thanks for the tip

One thing I don't think anyone has brought up yet is that with the change to speaker level instead of line level connection, there isn't really a need to use shielded cable any longer.

Of course!! So the cat6 shield doesn't even need to be grounded, right? I only need to worry about The amp and PSU grounds, correct?

Cheers
Sono

 

[sonolink]

[it might be good to break up the long cable run with series ferrite beads] -- Aren't ferrite beads rated in "inductance"? If so, what value would you recommend to be used?

[I wouldn't use it - because of the junctions] -- Do you mean.....LIKE THIS???..... Or???.....
View attachment 117729

Check post #103
Cheers
Sono

 

[sonolink]

I think I'll go with this amp finally:

https://es.aliexpress.com/item/1005...id=2023112507263515577450821769550007496923_1
How about this for a PSU? (the 12v/2A one)

https://www.aliexpress.us/item/1005...p4p_id=202311270847480918090364504643001627_0
Impressions?

Thanks!!
Sono

 

[ccaudle]

If I can measure them with a multimeter I'll check them out

You need to sweep a test signal across the frequency range, so it would be something you do with an audio interface (software like REW can probably do that, but you would need to do some work to calibrate the input and output levels of the audio interface if it does not have pretty reliable level settings available).

So the cat6 shield doesn't even need to be grounded, right?

If there is a shield present it should be connected to a defined location, you generally do not want fully floating metalwork because then you have really unpredictable behavior (maybe difficult to predict behavior would be more accurate, since it will depend heavily on the RF fields present).
Probably the safest course would be to connect the connector shield pins to chassis (only chassis, do not confuse shields with other circuit functions), but just don't use shielded cables. That way if shielded cables were used, or it was found to offer some benefit, the only thing needed is to change the cables, no changes to the boxes are needed.

[EDIT] Although if you commit to never using shielded cable you could go with plastic enclosures for the B boxes, which are likely quite a bit cheaper than metal.

 

[ccaudle]

I think I'll go with this amp

How about this for a PSU?

You are very much getting into "try it and see" territory. Buying random items from Alibaba is kind of a roll the dice situation, there are no datasheets, you don't really know how well the design was implemented, and it ships directly from China, so if you have problems you are pretty much on your own.
Sometimes the devices are cheap enough that it is worth just gambling on buying 50 at once, and throwing them away if they don't work. That is up to you and your budget (both financial and time) to decide.

All the parts you have chosen are relatively easy to wire up by hand, so make a prototype and see how it works. The cable connectors are probably fiddly (is that word used as commonly in the UK as the US?) to solder bare wires to, but should be possible, then just put a lot of hot glue on the pins to keep them stable and prevent shorting. The transformer pins are large and spaced far enough apart that shouldn't be a problem at all.
Cut the outer insulation off a little section of Ethernet cable and use the twisted pairs as hook up wire; it solders pretty nicely, is already twisted in pairs, and is easy to find. It will look a bit of a mess, but you should be able to connect everything up just sitting on your bench and verify if it will do what you need.

If I were using that small amp board with input from a pro or semi-pro style mixer output, I would make a little buffer board using a decent balanced input receiver, and then either remove the pot on the amp board and replace with a fixed divider suitable for nominal pro-audio levels, or turn the pot all the way up, glue the shaft in place with some Loctite, and add fixed attenuation to the output of the buffer board.
This would probably be my go-to device for input buffer, it has everything you need except for a couple of capacitors on the input:
TI INA1651 audio receiver

 

[sonolink]

You are very much getting into "try it and see" territory. Buying random items from Alibaba is kind of a roll the dice situation, there are no datasheets, you don't really know how well the design was implemented, and it ships directly from China, so if you have problems you are pretty much on your own.
Sometimes the devices are cheap enough that it is worth just gambling on buying 50 at once, and throwing them away if they don't work. That is up to you and your budget (both financial and time) to decide.

I agree. But spending 4-5€ for the 15w+15w power amp in Box A is a risk I can take

All the parts you have chosen are relatively easy to wire up by hand, so make a prototype and see how it works. The cable connectors are probably fiddly (is that word used as commonly in the UK as the US?)

It is indeed

My idea for Box B was to make a PCB onto which I'd solder the transformers, switchs, pots and RJ45 PCB mount connectors (2 for each PCB).
The PCB would then be secured by the switches and the pots screws to the enclosure. Then I would use these (clic on "Color: 4xA1024") as external connectors.
https://www.aliexpress.us/item/1005...2000030316220580!rec!ES!784183733!#nav-review

Why that? To avoid having to make 41 square holes!
I'm still sketching up how he Box A is going to be.
Any comments, ideas are very welcome as usual

Thanks
Sono

 

[ccaudle]

It seems to me, right now, that this thread is acting somewhat like a pinball in a pinball machine.....random ideas just bouncing around all over the place

To a large extent that is because the project was never fully described at the beginning. The first post was on Nov 1, which showed input coming from a stereo headphone signal, and it was not until Nov 21 in post #65 that OP clarified that actually the input was coming from an aux output of a mixer, and it was a single voice, so not only a different signal level than originally implied, but mono and not actually stereo.
That is often a problem on this forum, you can only answer the question that is asked, not the question which should have been asked.

You also need to consider and remember about the cost and time it will take for the assembly of this entire project.

For sure a consideration on a commercial project. This is GroupDIY and not Group "please design my small run commercial project for me" so likely a working assumption around here is that the project will be a one off, or only a small number built, so assembly considerations may lean toward trading off more manual labor for reduced low volume part or fabrication or assembly cost. That makes perfect sense if you are doing something as a weekend hobby project for your own use, but may be a different trade-off if the project is actually a bespoke commercial project where you have to account for the value of your time.

 

[sonolink]

For sure a consideration on a commercial project. This is GroupDIY and not Group "please design my small run commercial project for me" so likely a working assumption around here is that the project will be a one off, or only a small number built, so assembly considerations may lean toward trading off more manual labor for reduced low volume part or fabrication or assembly cost.

This is no commercial project. It's a one off for a friend. If it was my own DIY project I wouldn't be looking for ready made circuits on Aliexpress, I'd be building from scratch as I usually do with my DIY stuff.

Also, I don't completely agree with the pinball thing: true, I should have been much clearer at the start, but I had no clear idea, just a feeling to look in one direction (the balanced line level way). Thanks to the idea that Voyager10 brought up and that Hubbub developped and detailed, this thread is now a real and buildable thread in which many people have brought good ideas and pointed out errors or variants, and I'm now almost only left with "mechanical" matters. To me, from the learning POV it's been very interesting to see how a completely different approach was born from people's suggestions which is the reason why I love this forum and I am always thankful

So, now I need to find a quiet 12vdc/2A PSU and I'll be pretty much sorted to build this thing for my buddy. Please I would appreciate some feedback on my post #118.

Thanks again for all your input, ideas and suggestions
Cheers
Sono

 

[ccaudle]

This is no commercial project. It's a one off for a friend.

Yeah, I get that, especially with your comment about not wanting to cut square holes. Mostly a comment referring to frequent comments from MA about considerations that are more relevant for contracting out some of the assembly and fabrication tasks. He has expressed his preference for sending out chassis fab to a manufacturer, and that's certainly valid if you would rather spend your money than your time. Last time I looked at a small volume enclosure shop it was going to be something like $200 or $250 for a basic aluminum box with one rectangular hole and four or five round holes. I decide I would rather spend some time at my drill press with a blank Hammond enclosure and save $150 or $200.

now I need to find a quiet 12vdc/2A PSU

Your choice basically comes down to buying something cheap, and measuring and trying in your application to see if it works well enough, or just go with a reputable vendor like Meanwell, especially if you can find a model that someone has already measured and will vouch for the performance.

I notice you were looking at internal supplies, but most commercial equipment in this power range uses an external power supply so that you do not have to deal with AC line connector, fuses, etc. in your own enclosure. Just need a barrel jack style connector and then you have a choice of a wide range of supplies that are easy to swap out for a different one if the first one you pick is noisier than you want.

have been working on his project in a "behind-the-scenes" manner

I've been bitten by that on commercial projects as well. There is always a trade off, if you start running full speed before you know the direction (i.e. have a full specification to work to) you might luck out and get a head start. Or you might find out you ran in the wrong direction and just wasted energy.

 

[sonolink]

I notice you were looking at internal supplies, but most commercial equipment in this power range uses an external power supply so that you do not have to deal with AC line connector, fuses, etc. in your own enclosure. Just need a barrel jack style connector and then you have a choice of a wide range of supplies that are easy to swap out for a different one if the first one you pick is noisier than you want.

That's a very good point actually. Thanks for the tip, I'll go with that

 

[Hubbub]

My idea for Box B was to make a PCB onto which I'd solder the transformers, switchs, pots and RJ45 PCB mount connectors (2 for each PCB).
The PCB would then be secured by the switches and the pots screws to the enclosure. Then I would use these (clic on "Color: 4xA1024") as external connectors.
https://www.aliexpress.us/item/1005...2000030316220580!rec!ES!784183733!#nav-review

Why that? To avoid having to make 41 square holes!
I'm still sketching up how he Box A is going to be.
Any comments, ideas are very welcome as usual

Thanks
Sono

I would avoid having twice as many connection points as needed, ideally using a PCB mount RJ-45 that could be externally accessed. But I can appreciate that a PCB mount "XLR style" RJ-45 might not be readily available, so your choice does make some sense for minimizing the labor involved, and the servicability of the unit. I considered using the 4xA1027, which would allow using (0.1" ctrs?) flat flex wire cable that then solders to the main box PCB, but now the PCB becomes permanent to the box rear panel. Not the greatest for assembly or servicing. So maybe the 4xA1024 is it.

I'd note that the cover becomes just another dangly thing to be ignored, to break off, or get in the way. You may want to snip it off if not absolutely needed.

 

[sonolink]

I'd note that the cover becomes just another dangly thing to be ignored, to break off, or get in the way. You may want to snip it off if not absolutely needed.

You read my mind on that one!

 

[sonolink]

Question: in this context is it ok to use Cat8 instead of Cat6. Apparently my friend has a bunch of Cat8s laying around...

Cheers
Sono

 

[thor.zmt]

Does this version of this schematic NOW make sense? Bueller? Bueller?? Bueller???.....
View attachment 117728

This is directed at the scheme, not a specific poster.

If we keep the big power amp from earlier, to feed the signal (big is relative, something like LM1875 or LM3886 etc.), we get a fair bit of available level. Especially LM3886 can easily produce 20V.

I would suggest to place the transformer ahead volume control. Transformers perform best if driven from zero impedance and loaded optimally.

Earlier 100V transformers were mentioned, they are very inexpensive, correctly applied they perform well and give a fair bit of step-down, but they usually are autoformers (no isolation).

Small mains toroid's can also work. OEP has a 150R:25k transformer that can handle 5V/30Hz on the secondary, if operated reversed. Then a low resistance Pot can be used.

The key here would be to find a cheap and easily available transformer and then design both driving circuit and headphone feed around this.

Thor

 

[Hubbub]

Question: in this context is it ok to use Cat8 instead of Cat6. Apparently my friend has a bunch of Cat8s laying around...

Cheers
Sono

Cat-8 should work, but it will be a pain to properly install connectors on it. Got commercially made cables, fine, use them. Might be hard to come by with XLR style hoods. If you are installing your connectors onto cut lengths of cable stick with Cat-6. Also note that Cat-6 requires a different RJ-45 plug than that used for Cat-5x. I don't know what Cat-8 requires for proper termination as each pair is individually foil shielded, and the overall braid shield needs a connection too.

 

[Speedskater]

I lost track. What are you using the CAT cable for?

a] short length, line level analog audio.
b] long length, line level analog audio
c] headphone level audio.
d] digital audio AES/EBU
e] high speed digital data

different CAT cables for different applications.