2.5 mm TRRS Balanced (Legacy Portable Balanced)
Tip L+, ring 1 L-, ring 2 R+, sleeve R-. Replaced by 4.4 mm Pentaconn for mechanical fragility reasons.
Pinout
Pinout data not yet populated for this connector.
Specifications
| Diameter | 2.5mm |
|---|---|
| Pole count | 4-pole TRRS |
| Signal topology | balanced |
| Intended use | Legacy portable balanced headphone output (pre-2018) |
About this connector
The 2.5 mm TRRS balanced connector emerged in the early 2010s as portable-audio’s first attempt at delivering true differential balanced signal to IEMs from pocket DAPs. Four-pole layout: L+/L-/R+/R- with no chassis-ground pin.
Failed for mechanical reasons rather than electrical ones. The 2.5 mm shank diameter is half the cross-sectional area of 4.4 mm; cable strain at the connector exit ovaled the receptacle, broke the solder joints inside the plug, and made the connector the single least-reliable point in any portable balanced rig. JEITA’s 4.4 mm Pentaconn replaced it from 2018 onward.
Many cables, sources and DAPs from the 2014–2019 era still exist in the wild — bridge them with the 2.5 mm → 4.4 mm adapter or the 2.5 mm → XLR4 adapter. The SPC IEM cable still ships in this termination.
Compatible parts (MPNs)
| MPN | Form | Termination | Plating | Price (USD) | |
|---|---|---|---|---|---|
| SMT-25-B | Cable plug, straight | Solder | Gold over brass | $4 |