Project: Balanced 2.5mm to 4 Pin XLR Adapter

[Berwhale]

The days are getting shorter and the nights are closing in, so it's project time...

I want to plug my IEMs into my EX5. I have Moondrop Starfields with a 2.5mm balanced cable from Linsoul - the Starfields are usually connected to my Earstudio ES100. I'd like to use the 4 pole XLR connection on the front of the EX5.

Yes, I realize the 4 pole XLR on the front of the EX5 is not actually balanced and is there for convenience.

The 2.5mm TRRS to 4 pole XLR adapter from Drop would have been great! But they're not available right now. A similar adapter is over £20 from AliExpress or close to £40 if purchased in the UK.

So how expensive/hard can it be to make one? Let's find out...

2x 2.5mm, 4 pole panel mount sockets: £1.74
1x XLR Plug, 4 Pole, Black - Neutrik NC4MXX-B (only the best for me!): £5.95

The 2.5mm sockets didn't come with any schematics, so i'll have to work out the connections with the Linsoul cable and a multimeter...

Here's a close-up of the 2.5mm socket and 0.78 2 pin connectors...

Top pin on the left 0.78 2 pin connector goes to the long tab on the socket (bottom tab).
Bottom pin on the left connector goes to the medium length tab on the socket (top tab).
Top pin on the right 0.78 2 pin connector goes to the left short tab on the socket.
Bottom pin on the right connector goes to the right short tab on the socket.

So I think...

Long tab = L- = XLR pin 2
Medium tab = L+ = XLR pin 1
L Short tab = R- = XLR pin 4
R Short tab = R+ = XLR pin 3

Does this seem right? (I don't think it matters if I get + and - reversed, as long as i'm consistent for L & R)

It's too late to get the soldering iron out now, so I shall continue later in the week. Here's a nice shot showing how well the panel socket fits in the back of the Neutrik plug. The cable clamp will need to be reamed out so that it grips the socket, rather than pushing it out the plug

 

[Doodski]

Great project to post here. It seems even lately that one peep has inquired about how to do this.

 

[staticV3]

Does this seem right? (I don't think it matters if I get + and - reversed, as long as i'm consistent for L & R)

Seems right and I agree with you regarding the polarity.

Still, if you want to ensure that Cold stays Cold, then you can do that by probing the 3.5mm stock cable or the 2.5mm aftermarket one alone to figure out the 2pin connection, then plugging the 2.5mm socket in to figure out the pins on it.

 

[Berwhale]

I confirmed that the 'top' pins are -ve assuming this is correct...

Note: The software for my ES100 indicates that it's wired for A&K, which seems to be fairly standard these days.

 

[Berwhale]

Is there any issue using 24AWG solid core copper wire (from CAT5E cable) to connect the socket to the XLR plug? Can I leave the pairs twisted, or should I separate them? The wires will be 6cm long (<2 1/2").

 

[staticV3]

Is there any issue using 24AWG solid core copper wire (from CAT5E cable) to connect the socket to the XLR plug?

Since it'll be one solid adapter, solid core should be fine.

Can I leave the pairs twisted, or should I separate them?

Twisted pairs can be advantageous in audio, if you connect them the right way (one pair for ±R, the other for ±L)

 

[Berwhale]

Three layers of heat shrink made the socket fit snuggly in the back of the Neutrik plug...

I forgot to take of picture of the XLR soldering, but it was good (for an amateur!)

Finished article...

Tip: The 2.5mm socket needs to rotate when screwing the XLR plug together. I made the wires long enough so that the socket was outside the XLR barrel whilst it was screwed together. I then carefully pushed the socket back into the barrel (hoping the solid core wires bent gracefully). The rubberised end of the Neutrik plug 'grabs' the heat shrink wrapping and holds the socket securely.

Also... I checked continuity between the 0.78 pins and XLR pins and for shorts between any pairs of pins on the XLR plug before inserting the adapter into my EX5 and testing with my Moondrop Starfields. Everything seems to be working as desired

Lastly... I had to shorten the cable clamp by 3 or 4 mm. It wasn't possible to ream it out to grab socket and the lengths didn't work out anyway. I did consider shortening the whole XLR plug by cutting off the last part of the barrel, but I wasn't confident about doing this neatly enough to look good when finished.