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"Balanced"?

post #1 of 13
Thread Starter 
So I am in the process of purchasing a balanced-->se adapter for my headphones and was planning on using BJC to save a few bucks and wound up hearing some interesting claims regarding balanced headphones. I have no idea whether these statements are correct; that's why I'm starting this thread in the first place - I have no electrical background or experience.

Quote:
On a side note, it is erroneous to call the headphones "balanced" in the strict sense of the term. Any speaker, regardless of size or application (from headphones to concert systems), all take speaker level signals. Balanced audio is a line level signal type. There is no such thing as a "balanced speaker". Balanced audio reuires at least 3 conductors. Speakers use only 2 (+ and -). Having an XLR connector does not make it a balanced circuit, because on every one of the "balanced" headphones we've ever worked on, only 2 of the 3 XLR pins were utilized in a meaningful way.



The only way headphones could really accept a balanced signal would be for there to be an integral amplifier built into the headphones, and you would require a 5 pin connection, dual TRS, or dual XLR from the source.

...

I looked at the diagram you sent and, as I suspected, this is not a balanced circuit because the ground is tied with the negative on the speaker coil (which makes this a standard unbalanced circuit). A true balanced circuit has a completely separate ground from the conductors carrying the signal. As soon as you tie either one of the signal carrying conductors to the ground wire (which happens when you plug the cable into amp), it is no longer a balanced signal. Technically, as long as his cable design isn't plugged in, it could be considered a balanced cable. What negates it is the fact the the shields on the XLRs are tied to the same ground as the negative signal from the amp. This is an extremely inefficient way to connect unbalanced speker level signals, and I do not recommend it.



The writer of this article is quite mistaken about what is and isn't a balanced circuit. More on that can be read here: Blue Jeans Cable--A Question of Balance
For reference, the article was: Art. I- Balanced vs. Unbalanced - HeadRoom: Stereo Headphones, Amps & DACs, Wireless, Noise Canceling, Ear Canal, Earbud, Audio Cables & Accessories
post #2 of 13
Do you have the diagram mentioned handy? I don't see that in the Headroom article linked (I see shield tied to power ground).
post #3 of 13
If you flip through the entire sequence (link to "Article II" on the bottom of the page), all the diagrams are there.
post #4 of 13
If there are three conductors, and the negative conductor is tied to the ground, then yeah, it is not going to be a balanced signal anymore. You should not directly connect a negative signal to ground, because that is shorting the output. You could damage something. Using a transformer to turn a negative signal into ground, for balanced to single-ended conversion, is okay because you don't short the output.

The diagrams on HeadRoom's web site are clear in showing the balanced connection into the headphones is only connecting the negative and positive signals to the driver voice coil. This is fine, because the only purpose of ground is to provide a reference point. So you still get the benefits of noise rejection. The "ground" conductor isn't connected to anything at the headphone side. It only serves as a shield and anything it picks up is drained into the headphone amp's ground.

I did not see a diagram where the cable was tying a balanced cable's shield to negative. ???
post #5 of 13
Thread Starter 
Quote:
Originally Posted by WesMiaw View Post
If there are three conductors, and the negative conductor is tied to the ground, then yeah, it is not going to be a balanced signal anymore. You should not directly connect a negative signal to ground, because that is shorting the output. You could damage something. Using a transformer to turn a negative signal into ground, for balanced to single-ended conversion, is okay because you don't short the output.

The diagrams on HeadRoom's web site are clear in showing the balanced connection into the headphones is only connecting the negative and positive signals to the driver voice coil. This is fine, because the only purpose of ground is to provide a reference point. So you still get the benefits of noise rejection. The "ground" conductor isn't connected to anything at the headphone side. It only serves as a shield and anything it picks up is drained into the headphone amp's ground.

I did not see a diagram where the cable was tying a balanced cable's shield to negative. ???
Thanks for the clarification. I figured that the person probably just wasn't familiar with balanced headphones.
post #6 of 13
Quote:
Originally Posted by seacard View Post
If you flip through the entire sequence (link to "Article II" on the bottom of the page), all the diagrams are there.
Yes; but, like WesMiaw, I don't see one matching the OP's quoted text, with - tied to the shield.
post #7 of 13
Quote:
Originally Posted by WesMiaw View Post
If there are three conductors, and the negative conductor is tied to the ground, then yeah, it is not going to be a balanced signal anymore. You should not directly connect a negative signal to ground, because that is shorting the output. You could damage something. Using a transformer to turn a negative signal into ground, for balanced to single-ended conversion, is okay because you don't short the output.

The diagrams on HeadRoom's web site are clear in showing the balanced connection into the headphones is only connecting the negative and positive signals to the driver voice coil. This is fine, because the only purpose of ground is to provide a reference point. So you still get the benefits of noise rejection. The "ground" conductor isn't connected to anything at the headphone side. It only serves as a shield and anything it picks up is drained into the headphone amp's ground.

I did not see a diagram where the cable was tying a balanced cable's shield to negative. ???
x2.

also, i generally see the term "bridged" vs. "balanced" when talking about power amp topologies. they both pass an inverted signal to the (-)...no?
post #8 of 13

Balanced / bridged have both taken a toll on users pocketbooks I fear.  My own included.  For some interesting history and a clearer understanding of the confusion surrounding pro / consumer, balanced / SE, the component interconnection mess, and more, the RaneNotes on grounding and shielding and sound system interconnect are highly recommemded.  There be dragons here.

 

Headset cans respond in nearly all cases to a voltage DIFFERENTIAL.  If both inputs are 2volts higher or lower makes no difference to the mechanical force generated.  This is another way of saying that 'common noise' is rejected.  In components there are circuits that reject common noise also.  Components using these circuits are frequently called balanced.  Bridged amplifiers, whether balanced or single ended, can drive headphones and may sound better.  The ultimate is balanced DACs driving balanced headamps bridged across each can.  The result may fail more often, most likely will cost more based on component costs alone, but can result in truly beautiful music.  Minimizing distortion resulting from digitization of the original analog signals as well as that caused by subsequent reconversion to analog is a major issue.  Symmetric and complementary circuits, carefully matched components, and proper interconnect all contribute.  The chain is only as good as the weakest link.  That need not break your budget but frequently does :-(  It most frequently costs most based on hasty (re)purchase decisions.

post #9 of 13
balanced headphones use 4-conductor wire and usually with balanced 1/4'' TRS or DIN connector. only balanced headphones i know are vintage/discontinued studio headphones like the AKG 240 Sextett and Pioneer Monitor 10's. i knew of some vintage studio orthodyanmics like yamaha's and fostex that use balanced TRS 4-core connectors as well. to be balanced you need separate negative and positive for left and right channel. most speaker outputs of stereo amps had individual grounded speaker outputs for positive(send/hot) and negative(return/cold) signals. if not the ground was always same as the negative. ground is just used for shielding purposes as mention but is really not needed especially if you plain on using speaker outputs for your headphones.

i have my sextetts lp rewired for 4-pin XLR and works great off of speaker outputs and is more versatile. i wish more headphones used 4-core cabling and 1/4'' TRS jack but they always have to have it on an unbalnced 3.5mm jack for marketing reasons so they can target the everyday consumer. i only know of professional equipment using balance connectors far more then marketed audiophile gear.
post #10 of 13

To be a properly balanced connection, transformers are needed in the headphones to calculate the difference in the singal between the 2 wires and reject the added noise.

post #11 of 13
JRG1990, can't that also be done with an amp's output transformers?

Why would they have to be in the headphones?
post #12 of 13
Quote:
Originally Posted by JRG1990 View Post

To be a properly balanced connection, transformers are needed in the headphones to calculate the difference in the singal between the 2 wires and reject the added noise.


The voice coils in the headphones do that all on their own. No need for any transformers.

 

se

 

 

 

post #13 of 13
yea. as soon as you remove that shared ground connector the headphone will become balance. you can add a separate ground if you want but you don't have to cause the negative wire acts like a ground as well and the amplifier outputs would already will be grounded as well. The power transformer in an amp acts like a filter to block unwanted electrical and radio interference and is also used for impedance matching in most cases.
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