Balanced headphones are one of the best ways to experience the full audio potential of the Pono, or any other headphone amplifier that offers a balanced output stage. Balanced mode delivers 4x the power to your voice coils, cuts your signal-to-noise ratio by 4, doubles the signal slew rate, and eliminates channel-to-channel crosstalk. The result is a precipitous drop in your noise floor, almost unbelievable increase in audio detail, much fuller and precisely defined soundstage and imaging, and an overall warmer, richer and fuller sound reaching your ears.
Normal headphones are wired with one 'hot' wire for each voice coil, but a single ground wire shared by both coils for the signal return path. A normal headphone amplifier has one 'single ended' amplifier for each of the left and right voice coils. Which means it only drives the ‘hot’ wire to each of the voice coils, and relies on the shared return wire to complete the circuit. This system works fine for low to mid end audio. But it has several giant shortcomings if you want the best possible sound quality.
Balanced mode, on the other hand, drives both sides of each voice coil with separate amplifiers in a ‘differential’ fashion. When one amplifier is driving one side of the voice coil in the positive direction, the other side of the voice coil is getting simultaneously driven in the negative direction by the other amplifier. This simple tweak is all it takes to gain the massive benefits of balanced mode. But, unfortunately most headphone manufacturers don’t support this wiring because it’s more expensive to produce, and most audio device manufacturers don’t support balanced mode because it takes twice the number of amplifiers.
The designers of the Pono had the immense wisdom and forethought to include a Balanced output mode suitable for driving balanced headphones. So if you have a Pono, you already have half of what you need to get the full impact of balanced mode.
The other half of what you need is a set a headphones that are wired in a way that can accept a balanced signal. Balanced headphones are available on the market, but they are generally very expensive. Which is the point of this hack. We’ll show you how you can, with modest soldering and dremel’ing skills, convert a pair of Audio-Technica ATH-M50X-2ND studio monitor headphones from standard wiring to balanced wiring.
Balanced headphones are basically just normal headphones that have been rewired to replace the standard three-conductor ‘two hots and a ground’ cable with two new three-conductor cables, one for the left and one for the right. These new cables have each of their two signal wires connected directly to the corresponding voice coil leads, and the third conductor, which is the ground/shield, is simply cut and not connected to anything on the headphone side.
A Note of Caution: This hack requires careful wiring to avoid damaging your Pono!
Here are some of the tools you’ll need. You’ll also need a soldering iron, and a Dremel rotary tool (or a small rat-tail file could do)
The Audio-Technica ATH-M50X-2ND Studio Monitor headphones. We found a factory refurbished pair for about $120.
These are the new cables we’ll use. ‘Hosa Technology CMM-110’, they’re 10 ft. shielded cables with TRS jacks on both ends, about $5 each. Any similar cables should work as well.
Cut one of the TRS jacks off each of the cables.
Remove the foam ear cap from the side where the stock jack plugs in. The modifications will be done in this side only.
Remove the 4 screws to split open the headphone casing.
Remove the two screws holding the plastic strain relief, save these to be used later. Remove the two screws holding the small circuit board, save these also.
De-solder and remove the jack from the circuit board.
Using an Xacto knife, carefully cut the small trace on the circuit board that connects the two gold colored minus (-) voice coil leads together. Using an ohmmeter, verify that the two gold wires are now electrically isolated from each other.
With a Dremel or small rat-tail file, elongate the holes in the strain relief to allow both cables to fit through it.
Elongate the hole in the headphone casing where the jack was to allow both cables to fit through it.
Grind down the plastic ridge in the headphone casing where the strain relief sits to allow the audio cables to fit through.
Strip approximately 3/4" of outer insulation from the audio cables, cut and remove the shield wires. Strip and tin about 1/16" from the four signal wires.
Insert the audio cables through the hole in the headphone casing where the jack was, and then through the strain relief.
Reattach the strain relief in its original location. You may need to apply a bit of force to get it to seat properly.
Using large wire cutters, cut off the small tab from the circuit board where the jack was soldered. Replace the circuit board in its original location.
Carefully solder the new cable wires to the circuit board to make the connections to the headphone voice coils. Pay attention to polarity, of course. The red (+) wires solder to the outer pads, and connect to the green and red voice coil wires. The white (-) wires solder to the newly isolated center pads, and connect to the gold voice coil wires. Using an ohmmeter, verify that the tip and ring on each of the TRS jacks reads about 35 ohms (the voice coils DC resistances). Also verify on both TRS jacks that there is no connection from either the tip or ring to the ground sleeves (the largest third band on the TRS jacks). And finally, verify that there is no connection at all between the two new TRS jacks (check continuity from each band on each TRS jack to all the bands of the other TRS, there should be no connection at all between the two TRS jacks). CHECK THESE CAREFULLY!!!! Any short circuit will blow up your Pono! Seriously.
Replace the cover, and the 4 mounting screws. Be careful not to crimp any of the wires inside. Replace the foam ear cap. Double check again that the wiring continuity is still good after reassembling (re-run all the checks from step 17). The wires could break or short out when reassembling the phones.
Plug the TRS jacks into the Pono. Set the Pono to balanced mode (Settings -> Playback -> Balanced Mode).
That’s it. Now you’re in balanced mode!
Xkitz also offers a line of high grade audio amplifiers, bi-amplifiers and active crossovers that can accept the balanced audio signals from the Pono. Check out our website Xkitz Electronics