Some Common Headphone's Plug Wiring For Balanced Audio
Mar 27, 2018 at 2:37 AM Thread Starter Post #1 of 7


IEM Reviewer Extraordinaire
May 11, 2004
Mid Johor, Malaysia

*3.5PRO is a new standard proposed by the China Audio Industry Association Headphone Division and is said to be adopted by several Chinese manufacturers in the near future as an improvement over the original Hifiman proposed 3.5mm TRRS balanced plug. It is essentially just the same 3.5mm TRRS (wired the same way) with an extra plastic ring molded at the sleeve (shown in red on the picture above). The 3.5PRO socket will be more recessed to accommodate the extra plastic ring. The problem with Hifiman original proposed 3.5mm TRRS is that a single-ended 3.5mm TRS plug can be mistakenly inserted into the same socket and causes shorts. But a single-ended 3.5 TRS or normal 3.5mm TRRS plug will not be able to fully insert into the 3.5PRO socket and thus making sure no shorting out will occur. On the other hand, a headphone with the new 3.5PRO plug will still be compatible with an old 3.5mm TRRS balanced socket found on Hifiman and some LH Labs’ devices.

PDF can be found here.
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Apr 1, 2018 at 9:10 AM Post #3 of 7
is there anything similiar for 3,5mm dual mono sony pha-3?

PHA-3's balanced plugs are Tip = signal(+); Ring = signal(-); Sleeve = unused

Obviously you will need two 3.5mm plugs, one for the left and one for the right channel.
Dec 9, 2018 at 2:01 AM Post #5 of 7
Thanks for explaining 3.5PRO- couldn't quite divine the differences from TRRS scrying Chinese language announcements in auto-translate.

Arg @ all these balanced standards. I'm almost completely unified on 3.5 TRRS but it's still annoying - obviously my own fault for gear rolling so much, but lately am seriously considering just tossing everything and going back to SE exclusively. Maybe I have at last (d)evolved into my final form- "goodenoughphile".
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Oct 18, 2023 at 12:54 AM Post #6 of 7
Silly question on an old thread but I'm trying to figure out some pin out for a 2.5mm balanced cable I'm trying to make and I was using this OP as a guide.

I have a non-balanced 3rd party cable I want to switch to a 2.5mm balanced but I'm not sure which pins on it's Lemo connections should correlated to which contacts on the 2.5mm TRRS connector.

I've found lots of diagrams like this online but it's unclear to me if this is same layout I should use for the Utopia 2.5mm and if so which pins from the headphone side should correlate to these.

I did digging and figured out a possible mapping but I'm still not sure if it's correct.

I took the continuity measurements from the stock cable and attempted to map those to the R+, R-, L+, L- values on the headphone attachment side by using this guide. i.e. tried to figure out how a standard 3.5mm like the stock cable would translate the TRS to in terms of R+, R-, L+, L-. Then I translated the R+, R-, L+, L- values to the most common TRRS pinout I've seen which gives this.

Does it seem correct? I organized it by the balanced column but the stock TRS column having a different mapping / order makes me wonder if this is right.

Headphone sideStock 3.5mm2.5mm bal2.5mm bal
R2 (blank)SR-T
R1 (red dot)RR+R
L1 (red dot)TL+R
L2 (blank)SL-S
Oct 19, 2023 at 1:13 AM Post #7 of 7
Your description seems correct but you will be better to ask in the Utopia thread for confirmation as I have no idea how the Lemo connector on the Utopia is wired internally.

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