Balanced Headphone Drive

You may have heard some good things about 'Balanced Headphone Drive'.

Audiophile headphone aficionados will exclaim that balanced-drive is the ultimate nirvana of headphone listening, the cat's meow of cans, the creme de la creme of personal audio systems, the highest of the 'high end'.  

Our friends at HeadRoom Audio were the very first to design and market balanced headphone systems with the HeadRoom 'BlockHead' Balanced Amp way back in 1999. So no one knows more about balanced drive amplification and headphones than us.

 WHAT ARE BALANCED-DRIVE HEADPHONES?

In essence, balanced drive is a headphone amplifier design scheme that delivers 'balanced' equivalent and opposing [i.e., negative/positive] audio signals independently to each side of the headphone driver coils.

Balanced-drive delivers a noted increase in audio performance due to the doubling of the amp's voltage slew rate and voltage swing range, a reduction of THD (Total Harmonic Distortion) components and the avoidance of crosstalk due to the elimination of the common ground plane.

The end acoustic result lends an expansive, open-toned quality to the musical presentation with quicker dynamics, more refined detail, tighter low bass and very clearly pronounced mid-ranges. 

How Do I Get a Balanced Headphone System?

First, you need a balanced headphone amp and your headphone cord must be re-cabled to an XLR plug termination. 

For 'hard-wired' headphones, balanced recabling is an aftermarket process which alters the headphone connection from a standard 1/4" stereo plug to left/right balanced 3-pin or to a single 4-pin stereo XLR plug (depending on your particular balanced amplifier connection).

Of course, today's newer headphones with user-detachable cords make the cable changeover a breeze. Simply swap out the stock headphone cable with an aftermarket balanced option and, bam, you now have a balanced headphone.

Also, keep in mind only certain headphones can truly be effectively balanced due to connections at the headphone that requires a separate left/right, positive and negative signal. So some headphones may sport an XLR plug connection - but are not truly balanced on the inside!

Article I - Balanced Drive vs. Unbalanced Drive

We really didn’t know what was going to happen when we introduced the world’s first balanced headphone amplifier, the HeadRoom Audio BlockHead Balanced Amp, back in the day. We didn’t know if getting rid of the common ground on headphones would actually make much difference. We didn’t know if headphones could be successfully re-cabled to a balanced configuration. We didn’t know if balanced headphone drive was going to sound any better - or even if it would sound good.

We just knew it could potentially be done and that we had to give it a try. Man, are we glad we did; high-end balanced drive headphones sound pretty great!

Although our concept of balanced drive design is now found everywhere in the industry, its still a fairly recent idea, so we want to help you understand what the heck we’re talking about in this article.

THE UNASSUMING BUT ALL-IMPORTANT HEADPHONE PLUG

A normal headphone plug has three connections on it: the tip is left; the ring is right, and the sleeve is ground.

The tip connects to a wire that goes to the positive (+) lead of the left headphone driver coil; the ring connects to a wire that goes to the positive lead of the right driver. The sleeve connects to a wire that goes to both negative (-) terminals of the driver coil. This wire usually has a solder joint in the “Y” or in the earpiece where ground wire from the plug splits into separate wires that are connected to the negative terminals of the driver coils.

Bold Lines Showing Common Return Signal Path of Both Left & Right Channels

In normal headphone amps, the most important thing to note is that as the left and right channels of the amplifier drive the left and right driver coils, the return current from the drivers gets joined together and travels some distance before returning to the amp’s audio ground.

This common pathway has some significant electrical resistance from the wiring, solder joints, contact resistance at the plug/jack etc., which causes a common signal to appear at the negative terminal of both driver coils. This common signal (a low-level summation of the left and right channel) will generate low-level crosstalk and harmonic distortion in the headphone presentation.

Just how "low level" depends on the quality of the entire headphone and amplifier system audio chain, but it will always be there as a muddying factor - i.e., the background noise floor. However, there is one way to completely get around the pesky crosstalk problem: balanced headphones.

 

THE BALANCED HEADPHONE PLUG

In short, balanced headphones are just regular headphones that have been re-cabled to a different plug.

The normal three-conductor cable with the common ground connection plug is replaced with a cable that has four conductors: right positive and right negative conductors to the positive and negative connections of the right driver coil; and left positive and left negative conductors to the left driver coil.

The headphone cable itself then gets terminated to either a 4-pin XLR plug or two (dual) 3-pin XLR male connectors, depending on the balanced-drive connection required for your particular balanced headphone amp.

THE BALANCED HEADPHONE AMP

In balanced-drive headphone listening, a headphone amplifier is used that has “balanced” outputs wherein each channel has a normal audio drive signal and a mirror image inverted drive signal.

The big trick here is that there is no electrical “ground” plane to the headphones anymore, so there is no opportunity for the crosstalk distortion we described above to occur.

Well … there’s actually another big trick needed to pull this off: a headphone amp that makes perfect 'mirror-imaged' balanced signals to properly drive balanced headphones.

Article II- Differences Between Balanced Transmission and 'Fully Balanced' Headphone System

So we've learned how re-cabling headphones for balanced drive can improve headphone audio performance by getting rid of the common ground shared by the left and right headphone drivers.

But there are other sonic advantages to be gained by driving headphones in balanced mode. Unfortunately, “balanced” drive has a number of subtle nuances and meanings that need to be explained to fully understand what we are trying to accomplish.

 

HERE'S THE HARDCORE  BALANCED DRIVE TECH-SPEAK

The most common use of balanced audio signal transmission has actually little to do with driving headphones in balanced mode.

In many professional audio applications, signals are routed from place to place via balanced cables in an effort to reduce common mode interference from radio frequency (RF) noise sources like fluorescent lights and motors.

Because the voltage developed on the transmission line from RF interference is identical on both normal and inverted signal conductors, and because the balancing transformers only allow current flow when the signals are opposing, the common interference signal is canceled out.

This problem is not typically an issue even with single-ended headphones because the low output impedance of the power amp prevents a significant RF interference noise voltage from ever developing. But there are other excellent reasons to drive headphones with a particular type of balanced amplifier.

Certainly, there are a number of amplifier designs that are single-ended internally, but use transformer coupled outputs; these amplifiers improve headphone performance largely because of the removal of the common ground.

However, there is an entirely different approach that can be used to get significant and measurable performance improvements at a lower cost than would normally be available against the diminishing returns curve of component upgrades.

Often called “fully balanced” designs, this type of amplifier has completely separate and matching electronics circuits for all four (left normal and inverted, and right normal and inverted) audio signal paths.

The advantage of this design is that there are two power amps driving each coil; each amp effectively drives half the coil, with a virtual ground or zero voltage point halfway into the coil.

Since each amp is only driving half the load, a significant improvement in control can be achieved, and because the voltages are in opposition, an effective doubling of slew rate (volts per second the amp can swing) is realized compared to the normal slew rate of either amp by itself.

In other words, by doubling the amount of electronics circuits, a two-fold performance increase in some critical areas can be achieved with only a 50%-70% increase in cost. Normally, a doubling of measured performance would easily cost much more to achieve.

Next, we will continue by describing how we get a balanced signal to begin with, and how HeadRoom balanced amps, in particular, help you get it right between your ears.

Using a Balanced Sources  -   LP Phono Stage or Computer

If you’ve been reading along and have absorbed the gist of our balanced headphone articles, you’ll know that re-cabled, balanced headphones and fully balanced headphone amplification will get you improved audio performance ---but you have to use a fully balanced source. There are two we really like.

LP Vinyl Sources

Sure, digital audio has gotten very good (and we’ll get to that in a minute) but vinyl is organic and liquid-sounding, and just happens to be a way to get a balanced source, not to mention it provides hours of platter picking pleasure at record stores, too.

The coil within a phono cartridge is naturally balanced, and if you run it to a balanced phono amplifier, voila, you’ve got a truly balanced source. Tape heads make great naturally balanced sources, too. But if you thought vinyl was obscure try finding source material on 15-inch reels.

Digital Audio Sources

The proper way to get as close to perfectly balanced digital source as possible is to create the inverted channel by flipping while it’s still in the numbers stage. Normally, DACs (Digital to Analog Converters) run with 0000… giving a low voltage to 1111… giving its maximum voltage. In this case, the output with digital audio is non-inverted (or improperly but commonly called, “in-phase”). But with a simple toggle of a pin, the DAC inverts its word sequence and runs from 0000… giving the maximum output to 1111… giving it lowest voltage, which inverts the audio signal---pretty much perfectly.

 

 

Many balanced headphone amps also have DACs aboard with digital USB inputs or digital optical/digital coaxial inputs. That means your laptop could become a perfect digital source for a high-end listening system!

Balanced Drive FAQ

What is Balanced Headphone Drive?

Balanced Headphone Drive is a scheme that uses inverse positive/negative electrical paths to deliver equal and opposite audio signals to each side of the headphone driver voice coil.

When properly done, a significant increase of audio performance is heard due to the doubling of slew rate and power; the reduction of THD distortion components, and virtual elimination of crosstalk at the headphones due to elimination of the common ground plane present in standard 'single-ended' headphones.

Why Do I Need a Balanced Headphone Amp?

Because balanced drive requires two inverse audio channels at each ear instead of one, a balanced headphone amplifier outputs four (4) audio channels instead of the two normally found in a regular headphone amplifier. 

How Do I Know if My Headphones are Balanced?

If your headphone plug looks like the single plug on the left of the image, then your headphones are not balanced. The dual XLR connections on the right are an example of a balanced headphone plug type.

 

 

 Do My Audio Sources Also Need to Offer a 'Balanced' XLR Output?

In order to achieve the best performance from a balanced headphone system, a fully balanced audio source is needed. Many top CD players and audio components now offer XLR output connections.

There are also excellent Digital to Analog Converter (DAC) units with balanced XLR outputs that can act as a fully balanced source, so all you need is a computer via USB -- or an optical and/or coaxial digital SPDi/F audio signal from other audio components -- for your 'balanced' audio source.

What Type of Connector is Used in Balanced Drive?

There is no official industry standard for balanced headphone connections, and a handful of balanced connector configurations exist. One method uses two (stereo) male 3-pin XLR connectors, each carrying the normal and inverted audio channels, and shielded connections to their respective earpiece. This unique connection scheme uses a "combo" jack which includes both XLR and standard 1/4" stereo headphone jacks, so one amp that can drive both balanced and standard headphones. Additionally, a single 4-pin XLR plug can also be used to deliver a fully balanced signal. 

Does That Mean I Can Plug My Standard Headphones Into a Balanced Amp and Get a Balanced Signal?

No.  But you can listen to standard headphones on a balanced headphone amp just fine, you're just not listening in true balanced mode.

How Do I Get My Headphones Recabled and Ready for Balanced Drive?

The Sennheiser HD800S can be quickly re-cabled for balanced drive using the Cardas Balanced Cable for HD800.  If you own Sennheiser HD600/HD650 or AKG headphones, aftermarket balanced cabling is available for those cans. Audeze, Mr. Speakers, Oppo and HiFiMAN planar magnetic headphones also have detachable cables allowing for easy cord upgrading. 

 

Why Don't All Headphones Come in Balanced Models?

The time and significant expense that comes along with balanced-drive systems is generally warranted only for the very best-performing headphones. Moreover, even some 'high end' headphones cannot truly be balanced due to their internal wiring construction and/or other design issues.

Can My Headphones Function Both as Balanced Headphones and Single-Ended Headphones?

Yes, you just need to choose headphones with detachable cables allowing for an aftermarket balanced headphone cord. So you can purchase a balanced cable and just switch out the headphone cord(s) for single-ended or balanced listening as needed.

Besides Replacing Connectors, Is The Type of Actual Cable Different w/ Balanced Headphones?

Yes, the cable braid must have at least four conductors to get the proper balanced signal to the headphones. One example is Cardas, one of the finest cable manufacturers in the world, is internally structured to provide shielding and separation of the left and right channel pairs to reduce crosstalk.