Quick Answer / Summary: For stereo, wire the tip (left) to pin 2 of XLR-A, the ring (right) to pin 2 of XLR-B, the sleeve to pin 1 of both, and tie each XLR’s pin 3 to its own pin 1. For mono sum, route tip and ring to a single XLR pin 2 through 1 kOhm balancing resistors and the sleeve to pin 1. Both keep the signal unbalanced at the XLR pins, which is acceptable for short patch runs under 5 meters.
A 3.5 mm TRS jack carries a stereo pair on a single plug – tip is left, ring is right, sleeve is ground. Splitting that pair across two XLR lines, one per channel, is the standard way to feed a stereo 3.5 mm source into a mixer’s balanced inputs, and the wiring has two correct variants: stereo split (left on XLR-A, right on XLR-B) or mono summed on a single XLR. Choosing wrong costs you a channel or a phase flip, so this guide covers both topologies with full pin maps.
Two Wiring Topologies for One Plug
The destination determines the topology. If the XLR side has two inputs (two channels on a mixer, two XLR jacks on a recorder), use stereo split: each 3.5 mm pole gets its own XLR channel and the stereo image survives. If the XLR side has one input, use mono sum: both audio poles collapse into one channel, and the resistor decision determines whether the sum is clean or overloaded.
Stereo Split: One XLR per Channel
Tip to XLR-A pin 2, ring to XLR-B pin 2, sleeve to both pin 1s, and each XLR’s pin 3 tied to its own pin 1. The two channels are electrically independent after the split, so the mixer can EQ, pan, and level them separately. This is the correct wiring for any stereo player into a mixer’s channels 1-2.
Mono Sum: One XLR for Both Channels
Tip and ring both to pin 2, sleeve to pin 1, pin 3 to pin 1. If the source is a true stereo mix being collapsed to mono, route each pole through a 1 kOhm resistor before they meet at pin 2 – the resistor isolates the two sources so they do not load each other, keeps the sum phase-correct, and prevents the pin 2 node from seeing double the drive current.
Phase and Polarity on the Summed Version
Directly tying tip and ring to pin 2 without resistors works for many sources but is a parallel connection: if either source drives hard, the sum node sees twice the current and can distort, and a polarity error in one leg inverts that channel’s phase in the sum. The 1 kOhm-per-leg resistor sum is the industry fix – it costs a fraction of a dB in level and removes both failure modes. For critical mono sums (vocals, kick drum, lead instrument), always specify the resistor version.
Where Unbalanced-at-XLR Is and Isn’t Acceptable
An XLR connector does not make a signal balanced – only the wiring does. In both topologies above, each XLR carries a single unbalanced signal on pin 2 with pins 1 and 3 as ground. For patch runs under 5 meters in a normal environment, that is fine: the XLR housing’s mechanical robustness is the benefit, not noise rejection. For longer runs or noisy environments, the correct answer is not a better 3.5 mm cable but a balanced re-pairing at the source – a stereo line-level source should stay on balanced cabling end to end.
3.5 mm TRS to XLR Wiring Maps
| Topology | Tip (L) | Ring (R) | Sleeve | XLR Pin 3 | Use Case |
|---|---|---|---|---|---|
| Stereo split | XLR-A pin 2 | XLR-B pin 2 | XLR-A pin 1 + XLR-B pin 1 | Tied to own pin 1 | Stereo player into mixer channels 1-2 |
| Mono sum | Pin 2 via 1 kOhm | Pin 2 via 1 kOhm | Pin 1 | Pin 1 | Stereo source into a single XLR channel |
Real-World Application Scenarios
DJ and laptop stereo out into a mixer’s two line inputs. Video camera stereo line-out splitting across two recorder channels for backup. Studio patching where a stereo 3.5 mm source must reach two balanced XLR destinations. Broadcast automation, where the mono-sum version feeds a single XLR input from a stereo player. Both topologies appear in the same venue, which is why integrators stock both builds.
Recommended Internal Resources
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Frequently Asked Questions (FAQ)
Q: Can I split a 3.5 mm TRS plug into two XLRs?
A: Yes – wire the tip to XLR-A pin 2 and the ring to XLR-B pin 2, with the sleeve to both pin 1s. The stereo image survives as two independent channels, each of which can be levelled and EQ’d separately at the mixer.
Q: Do I need resistors when summing TRS to a single XLR?
A: For a clean, phase-correct mono sum, yes – one 1 kOhm resistor per leg before the poles meet at pin 2. Without them the sum can overload and a polarity error in one leg inverts that channel’s phase.
Q: Is a 3.5 mm TRS to XLR connection balanced?
A: No. The XLR connector is balanced-capable, but this wiring carries an unbalanced signal on pin 2 with pin 3 as ground. That is acceptable under 5 meters; beyond that, keep the source on true balanced cabling.