Balanced vs Single-Ended Headphone Amp: Specs Compared

The balanced vs single ended headphone amp question is usually argued on sound, which is where it is least decidable. It is far easier to settle on the spec sheet, because a balanced headphone output changes exactly four things that can be printed: voltage swing, output impedance, noise floor and connector. Two are improvements, one is a mild regression, and one is where most of the real-world benefit comes from. None of them makes an adequately driven headphone sound different once levels are matched. The word “balanced” is also doing two jobs in this market, and conflating them is how people buy cables they did not need.

Two different things called balanced

The first meaning belongs to line-level interconnects: the XLR or TRS link between a DAC and an amplifier. Jensen Transformers’ paper on balanced interfaces is blunt about what makes that link balanced: “signal symmetry has absolutely nothing to do with noise rejection.” Impedance is what matters. Both conductors have the same impedance to ground, so interference lands equally on both and cancels in a differential receiver, which is why Rane’s Note 110 calls it the only way to guarantee a hum-free link between two mains-powered boxes.

The second meaning belongs to headphone outputs, and it is a different circuit. A bridged or “balanced” headphone output uses two amplifiers per channel driving the two wires of each driver in opposite polarity, with no shared ground return. There is no receiver at the far end to reject anything. As Benchmark’s application note puts it, “the headphone drivers are completely ignorant of the difference between single-ended and balanced-drive voltages.” The Jensen paper quotes the annex of IEC 60268-3 on what symmetry does buy: its advantages “concern headroom and crosstalk, not noise or interference rejection.” Those two words are where a balanced headphone output can earn its keep.

What changes on the spec sheet

Schiit publishes both outputs of the same amplifier side by side, so the Jotunheim 3 specification page is one power supply feeding one topology two ways.

Load	Single-ended	Balanced	Ratio
32 ohms	2.0 W	6 W	3.0x
300 ohms	330 mW	1.2 W	3.6x
600 ohms	165 mW	600 mW	3.6x
Output impedance	under 0.4 ohms	under 0.8 ohms	2x
SNR (ref. 2 V / 4 V)	over 124 dB	over 128 dB

Bridging doubles the voltage across the load, and power rises with the square of voltage, so the theoretical ceiling is four times the single-ended figure. Real designs land below it, and at low impedance the output stage runs out of current before it runs out of volts. iFi’s ZEN CAN 3 specifications show this directly: balanced delivers 385 mW into 600 ohms against 98 mW single-ended, but into 32 ohms the balanced output is rated at 1,200 mW while the single-ended jack is rated higher, at 1,600 mW. Doubled swing only pays where the load is high enough for voltage to be the limit.

Output impedance doubles because the load sees two output stages in series: under 0.4 to under 0.8 ohms on the Jotunheim 3, under 1 to under 2 ohms on the ZEN CAN 3. Benchmark states it as “the damping factor will degrade by a factor of 2.” At these values it only starts to matter for a low-impedance in-ear with a swinging impedance curve.

For the same specification across amplifier topologies, compare tube versus solid state output impedance before choosing by connector alone.

The noise line needs care. Schiit’s balanced SNR is 4 dB better, but it is referenced to 4 V rather than 2 V, so the reference moved by 6 dB. Worked back to an absolute noise voltage, the balanced floor sits near 1.6 microvolts against roughly 1.3 microvolts single-ended, which agrees with Benchmark’s statement that “the output noise will double because there are two amplifiers instead of one.” Both figures are inaudible on a 97 dB per volt headphone, but the SNR line is not evidence that balanced is quieter.

Where the extra swing matters, with the arithmetic

Take a Sennheiser HD 600: 300 ohms, 97 dB at 1 V. A 110 dB peak needs 13 dB above 1 V, about 4.5 V RMS, or roughly 67 mW into 300 ohms. The Jotunheim 3’s single-ended 330 mW into 300 ohms is about 10 V RMS, which puts the HD 600 near 117 dB before the balanced output enters the picture. A balanced cable for this pairing adds swing the headphone cannot use.

On a battery the picture flips, and Benchmark’s note concedes the case: balanced “can deliver 4 times the power for a given power supply voltage. However, this would only be necessary if the product was battery operated.” The Qudelix-5K is the textbook example: 2.0 V RMS from the 3.5 mm jack, 4.0 V RMS from the 2.5 mm balanced jack, same battery. Into the HD 600 that is roughly 103 dB against 109 dB of peak level, the difference between running out of volume on a quiet recording and not. It is the one scenario where the balanced cable is the cheapest fix available.

The DAC and amp power sizer turns your own headphone’s impedance and sensitivity into the voltage you need, so check the single-ended column before assuming you need the other one.

The ground return is where the audible benefit lives

A 3.5 mm or 6.3 mm TRS plug carries left and right on tip and ring and returns both through one sleeve. Every ohm of contact and cable resistance in that shared return is common to both channels, so one channel’s return current develops a voltage the other channel hears. That is crosstalk, and it worsens with a worn jack, a thin cable or a low-impedance headphone drawing more current.

A four-conductor connection removes the shared path, and Benchmark’s own HPA4 shows the benefit belongs to the connector rather than to bridged drive. Its application note explains that the HPA4’s 4-pin XLR is “not driven with a voltage-balanced signal” and instead “provides isolated left and right ground returns” to each channel’s amplifier. That is a single-ended amplifier with a four-pin socket. Few products are built that way, but it is worth knowing which part is doing the work.

Connectors and the adapter trap

The 4-pin XLR is the desktop standard. The 4.4 mm five-pole plug is the portable standard, defined by JEITA RC-8141C in 2016 and documented on Pentaconn’s specification page as tip L+, ring 1 L-, ring 2 R+, ring 3 R-, sleeve ground. The 2.5 mm TRRS plug it replaced is fragile and fading. None ships in the box with most headphones; the HD 600 comes with a 3.5 mm plug and a 6.3 mm adapter, so a balanced cable is a separate purchase.

Stepping a balanced-terminated cable down to a TRS plug is fine. The reverse is not: a bridged output drives the L- and R- pins actively, and a passive adapter that ties them together and to ground shorts two amplifier outputs into each other.

The decision

Buy for the balanced output when the device runs on a battery and your headphones need more than about 2 V RMS, when you already own a balanced-terminated cable, or when the single-ended jack is rated below what the arithmetic says you need at your load. Ignore it when a desktop amplifier’s single-ended output already covers your headphones with margin, which the guide to matching a DAC and amp to your headphones shows is the common case.

Keep the two meanings separate when you shop. A balanced XLR link between DAC and amplifier is the interface kind and its hum rejection is real; the same logic drives the XLR and TRS inputs on studio monitors. If the reason you are shopping is a hum you already hear, work through the causes of headphone amp hiss and hum first, because a bridged headphone output does nothing about a ground loop between two chassis.

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