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Why Balanced Headphone Amps? - Page 3

post #31 of 120
Thread Starter 


Definitely a big improvement over my description, thanks!!

Yes, twisted pair will help with induced noise transmission (and I prefer twisted speaker wire for this reason), though this is not a function of the speaker being considered a balanced device, is this correct?

 

Quote:
Originally Posted by jcx View Post



 


you're not clear on common mode vs differential in that instance

 

the only way line noise couples to speaker cabling with audible result is through differential coupling - a time varying magnetic field from the outside induces a V difference when it "threads the loop" of the +/- speaker cable wires - just like a air core transformer

 

twisting wire helps for mag fields that are uniform over several times the twist pitch rate because the field induces mostly canceling V in each opposite orientation loops of the twist - star quad or coax can be even better

 

but if you measure the common mode V at the end of these high (differential) canceling cable constructions you still measure a V difference induced by the changing mag field that is equal in both wires and gives no output from the speaker
 

post #32 of 120

as I said above you could look at any 2-terminal device as an ideal "balanced" load/receiver but this certainly isn't really related to other common usages of "Balanced"

 

since the word can be correctly used several ways and you can have stronger weaker opinions on what is "misapplication" or even abuse of the term

 

the bridged output "balanced" opposing polarity amplifiers without differential feedback and no common mode rejection are not "fully" meeting some (useful) definitions of "balanced"

post #33 of 120
Quote:
Originally Posted by sbradley02 View Post

http://en.wikipedia.org/wiki/Balanced_audio

The purpose of balanced inputs and outputs is common mode noise rejection. That is it. For this to work, you must have a device that takes the sum of two signals of opposite polarities, i.e. a differential pair: http://en.wikipedia.org/wiki/Differential_pair

I can't see how noise that is conducted equally to both terminals of a moving coil speaker (whether you are using a bridged amplifier or a ground referenced amplifier doesn't make any difference here) results in the elimination of said noise.

I have done home audio installs. It is a guideline to never allow a speaker line to parallel a power line less than a foot away (preferably further). Failure to follow this can result in 60Hz conducted into the speaker line. The speaker will not, under any circumstances, reject this 60Hz interference. Not with a push pull amp, not with a bridged amp, not with any amp.

The definition of balanced signals is well and precisely defined in the industry. Changing the meaning of those terms is counter-productive.
 

Bridged amplifiers are not balanced. Headphones (with the possible exception of electrostatics) are not balanced. Neither will reject common mode noise.

If this is in error, and you have examples of these devices able to reject common mode noise, please provide that so we can go over it further.

Since most amplifiers use large amounts of global negative feedback, any induced 50/60Hz signal from parallel proximity of power lines to audio out lines will result in this induced 50/60Hz being re-amplified by all stages of the amp through the feedback loop in the amp.  Any induced hum by itself would never be enough energy to excite the speaker directly.  Twisted pair speaker wires are recommended in these cases in any event, so that coupled interference is cancelled out by the continual twists of the cable.

 

In any event, in a small, local, properly designed and lead dressed system, common mode induced noise should not be an issue.  In larger installations, I've done battle with many RFI monsters being detected by diodic elements in a system after being received by long mic lines, for example, even in some cases, when they were balanced lines.  Obviously, in those cases, the induced interference was not symmetrically coupled
 

post #34 of 120
Quote:
Originally Posted by Steve Eddy View Post

How does that description differ from the description of the primaries of the input transformers that I use? There are two wires coming out, one for each end of the one primary winding and that's it.

 

Yet the inputs of my input transformers are indeed balanced.

 

se


The input transformers to which you refer have center taps on those windings allowing the center tap to be a zero reference and each of the other input winding taps represent the entire length of the input winding with the input signal differentially balanced around the center tap.  That, is the classic use of true "balanced" circuits, so that any interference is mutually coupled to each of the differential pairs and thus summed and cancelled out at the point of termination.

post #35 of 120
Quote:
Originally Posted by sbradley02 View Post

http://en.wikipedia.org/wiki/Balanced_audio

The purpose of balanced inputs and outputs is common mode noise rejection. That is it.

 


Pretty much, yes.

 

Quote:
That is it. For this to work, you must have a device that takes the sum of two signals of opposite polarities, i.e. a differential pair:

 

Actually, common-mode rejection has nothing to do with signal polarities, or indeed signals at all. Consider: Balanced interfaces reject common-mode noise even in the absence of any signal.

 

Quote:
I can't see how noise that is conducted equally to both terminals of a moving coil speaker (whether you are using a bridged amplifier or a ground referenced amplifier doesn't make any difference here) results in the elimination of said noise.

 

Because a moving coil speaker is a differential input.

 

Think for a moment.

 

A dynamic loudspeaker only works because of current flowing through its voicecoil.

 

Apply equal voltages of the same polarity to each of its terminals.

 

How do you manage to get any current to flow?

 

1V - 1V = 0V.

 

Since I = E/R, 0V/R = 0.

 

Quote:
I have done home audio installs. It is a guideline to never allow a speaker line to parallel a power line less than a foot away (preferably further). Failure to follow this can result in 60Hz conducted into the speaker line. The speaker will not, under any circumstances, reject this 60Hz interference.

 

Well, first, the typical multiway loudspeaker isn't exactly balanced. The series crossover elements are used only on one side, which creates an imbalance in the source impedance, and as the source impedance becomes imbalanced, common-mode rejection diminishes.

 

But beyond that, provided that the 60Hz interference is received equally in both lines, i.e. common-mode, the driver would indeed reject it.

 

Quote:
The definition of balanced signals is well and precisely defined in the industry. Changing the meaning of those terms is counter-productive.

 

I've not changed any meanings if any terms.

 

Quote:
Bridged amplifiers are not balanced.

 

Technically they are, as "balanced" refers to a balance of impedances.

 

What they are not is differential, which means they cannot reject common-mode noise. Common-mode noise at the input of a bridged amp is simply amplified and passed along to its output.

 

Quote:
Headphones (with the possible exception of electrostatics) are not balanced.

 

Yes, they are. Their voicecoils are effectively symmetrical.

 

Quote:
Neither will reject common mode noise.

 

Bridged amplifiers will not because they're not differential. Headphones will as they are differential.

 

se

 

 

 

 

 

post #36 of 120
Quote:
Originally Posted by Steve Eddy View Post

Pretty much, yes.

 

Actually, common-mode rejection has nothing to do with signal polarities, or indeed signals at all. Consider: Balanced interfaces reject common-mode noise even in the absence of any signal.

 

Because a moving coil speaker is a differential input.

 

Well, first, the typical multiway loudspeaker isn't exactly balanced. The series crossover elements are used only on one side, which creates an imbalance in the source impedance, and as the source impedance becomes imbalanced, common-mode rejection diminishes.

 

But beyond that, provided that the 60Hz interference is received equally in both lines, i.e. common-mode, the driver would indeed reject it.

 

Technically they are, as "balanced" refers to a balance of impedances.

 

What they are not is differential, which means they cannot reject common-mode noise. Common-mode noise at the input of a bridged amp is simply amplified and passed along to its output.

 

Bridged amplifiers will not because they're not differential. Headphones will as they are differential.

 

se


Steve, picking at semantic nits will not help the average headphone enthusiast make better informed choices.  So let's try to disambiguate terms rather than to convolute them, please.

post #37 of 120
Quote:
Originally Posted by sbradley02 View Post

So lets say for some reason we have a pair of push-pull or single ended amplifiers with mediocre measurements (I am not sure why the we would be starting with units that don't measure well, but lets ignore this for now) in a bridged configuration. What seems to be claimed here is that the two amplifier sections would produce distortion products out of phase and would therefore cancel at the load. Is this indeed the reasoning behind this claim, or is something else going on? If so the amplifiers would have to be matched to an astonishing degree. And measurements would show this result. Do you have any example measurements we could look over?

 


If the phases in the push-pull amplifier are locked together properly with CCS's at junction points (cathodes in tubes, various places depending how the circuit is set up in SS amps) the phases have no choice but to lock together and distortions cancel very nicely.

 

 

Quote:
Originally Posted by sbradley02 View Post
 

I have often seen the claim that great sounding amplifiers should not  measure well. I don't buy it (yes some measure poorly but I don't see this as a requirement for good sound). And yes I am going to use speaker amplifier examples because that is what I have more experience with.

For tube amplifiers it doesn't get much better than Audio Research. Here's an example: http://www.audioresearch.com/Reference110.html. 0.3% THD at full power which is exceptional for a tube amp, and .03% at 1W which is excellent by any standard, and in the headphone power range.

 


You do know that the AR amp you linked to there is balanced from end to end. Fourth paragraph, top line. 

 

Regarding "great amps should not measure well"

No, they should not, although at the same time they might. Measuring very well should not be a prerequisite for someone comparing an amp or stating that they think it sounds great. The amp should be tested by ear fairly (blindly if possible) but to exclude amps that measure worse than a certain threshold from "great sound" would be folly. 

 

On that note, many (many) people abhor the use of feedback in amps for any number of reasons - "good" being totally subjective they have every right dont they? If you find yourself in this camp you have very few real options in changing how an amplifier sounds/perfdorms. 

 

Quote:
Originally Posted by kwkarth View Post

Yes, you are right, some electrostatic headphones are a true bipolar/balanced load where charge on the stators on either side of the statically charged diaphragm are modulated with the audio signal.  I don't know of any dynamic "speakers" that are balanced.  There is a voice coil with two wires coming out, one for each end of the one voice coil wire and that's it.
 


Funny, I dont know of any dynamic transdeucers that are single ended, with the odd exception of cheap junk that uses the frame of the transdeucer as ground.

 

Where is the ground on a dynamic driver? Dont point to the wrong terminal... it could be the other one. Or it could be NEITHER and you could float the speaker. Balanced systems do not require a ground reference.

post #38 of 120

Let's see if I understand this...

 

"Balanced" amps as is commonly understood on Head-Fi are mostly not truly balanced because they do not provide common-mode noise rejection in and of themselves. They merely amplify the balanced signal from a DAC.

 

But when a headphone transducer is fed a balanced signal, it will reject common-mode noise. Doesn't matter whether the amp was bridged or what not. Just that the signal from the source must  be balanced, and not converted to single ended along the way.

 

Corrections are welcome.

post #39 of 120

 

Quote:
Originally Posted by Yoga Flame View Post

Let's see if I understand this...

 

"Balanced" amps as is commonly understood on Head-Fi are mostly not truly balanced because they do not provide common-mode noise rejection in and of themselves. They merely amplify the balanced signal from a DAC.

 

But when a headphone transducer is fed a balanced signal, it will reject common-mode noise. Doesn't matter whether the amp was bridged or what not. Just that the signal from the source must  be balanced, and not converted to single ended along the way.

 

Corrections are welcome.


headphone transdeucers ALWAYS reject common mode noise. The issue at hand is that in a single ended system there is no common mode noise (one terminal is signal+noise, One is ground - there is nothing common) so the rejection is not obvious. If there is common mode noise, as in a balanced system it is very easy to demonstrate headphones rejecting common mode noise. 

 

The problem in defining "balanced" is that many single ended triode amps float the secondaries (outputs) of the transformers to get a balanced signal, but get none of the benefits to the active stages that an "end to end" balanced amp gets. 

 

After that there is the debate over whether its worth running a balanced cable less than 3 ft from a line level source (im assuming about 2v signal, which seems common) to a headphone amp, as is common in a headphone system. I'm on the fence here. you will not pick up noise in 3ft of cable with a line-level signal in a domestic enviroment. OTOH, there are still the benefits to balanced active circuitry so save yourself the phase splitter... balanced DACs are not really any more expensive than SE dacs.

post #40 of 120
Quote:
Originally Posted by nikongod View Post

Funny, I dont know of any dynamic transdeucers that are single ended, with the odd exception of cheap junk that uses the frame of the transdeucer as ground.

 

Where is the ground on a dynamic driver? Dont point to the wrong terminal... it could be the other one. Or it could be NEITHER and you could float the speaker. Balanced systems do not require a ground reference.

Please, tell me, what is it you are trying to cling to?  Are trying you confuse the average reader?  Are you trying to have the last word?  Do you need to be right?

 

If it will make you feel better, have the last word, but please stop confusing the average hobbyist with meaningless semantic blather.  
 

post #41 of 120
Quote:
Originally Posted by Yoga Flame View Post

Let's see if I understand this...

 

"Balanced" amps as is commonly understood on Head-Fi are mostly not truly balanced because they do not provide common-mode noise rejection in and of themselves. They merely amplify the balanced signal from a DAC.

 

But when a headphone transducer is fed a balanced signal, it will reject common-mode noise. Doesn't matter whether the amp was bridged or what not. Just that the signal from the source must  be balanced, and not converted to single ended along the way.

 

Corrections are welcome.


What we seem to be going in circles about, to the continued detriment of the average hobbyist, is the most acceptable definition of the term "balanced."

post #42 of 120
Quote:
Originally Posted by nikongod View Post

headphone transdeucers ALWAYS reject common mode noise. The issue at hand is that in a single ended system there is no common mode noise (one terminal is signal+noise, One is ground - there is nothing common) so the rejection is not obvious. If there is common mode noise, as in a balanced system it is very easy to demonstrate headphones rejecting common mode noise. 

 

The problem in defining "balanced" is that many single ended triode amps float the secondaries (outputs) of the transformers to get a balanced signal, but get none of the benefits to the active stages that an "end to end" balanced amp gets. 

 

After that there is the debate over whether its worth running a balanced cable less than 3 ft from a line level source (im assuming about 2v signal, which seems common) to a headphone amp, as is common in a headphone system. I'm on the fence here. you will not pick up noise in 3ft of cable with a line-level signal in a domestic enviroment. OTOH, there are still the benefits to balanced active circuitry so save yourself the phase splitter... balanced DACs are not really any more expensive than SE dacs.


Well said!!  Really, very good!

post #43 of 120

 

Quote:
Originally Posted by kwkarth View Post

Please, tell me, what is it you are trying to cling to?  Are trying you confuse the average reader?  Are you trying to have the last word?  Do you need to be right?

 

If it will make you feel better, have the last word, but please stop confusing the average hobbyist with meaningless semantic blather.  
 


You said that there are basically no balanced headphone drivers. This is not true. Almost all headphone drivers are balanced. Its simply a question of which cables & amps you hook up to them whether they show it or not.

post #44 of 120
Quote:
Originally Posted by nikongod View Post

 


You said that there are basically no balanced headphone drivers. This is not true. Almost all headphone drivers are balanced. Its simply a question of which cables & amps you hook up to them whether they show it or not.

Whatever, I just hope this does not confuse the readers, after your excellent post previously.
 

post #45 of 120
 
Quote:
Originally Posted by kwkarth View Post

Steve, picking at semantic nits will not help the average headphone enthusiast make better informed choices.  So let's try to disambiguate terms rather than to convolute them, please.


Ok, what terms should I disambiguate?

 

se

 

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