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Why Balanced Headphone Amps? - Page 8

post #106 of 120

I wonder if it is more of the fact that:

 

"The two antiphase outputs are connected to the load in a way that causes the signal outputs to be added, but distortion components due to non-linearity in the output devices to be subtracted from each other". Isn't that the very definition of balanced?"

--Balanced Amp Wiki

 

It appears that the Balanced Ultra Desktop Amp is a type of push-pull ( analog case ).

 

One of the best ways to reduce noise is by using a differential amplifier.

 

I found a thread for anyone who wishes to read more about push-pull and balanced amplifiers.

 

http://www.head-fi.org/t/595246/difference-between-push-pull-and-balanced

 

In the end, if the BUDA is differential regardless of being in single ended vs balanced, I cannot fully explain why I hear less blurring in the bass and better soundstaging.

 

I will try to get someone from Headroom to comment on the topology of their BUDA.  Perhaps when the single ended selector is active the amp is no longer truly differentiating??

post #107 of 120
Quote:
Originally Posted by NA Blur View Post

I wonder if it is more of the fact that:

 

"The two antiphase outputs are connected to the load in a way that causes the signal outputs to be added, but distortion components due to non-linearity in the output devices to be subtracted from each other". Isn't that the very definition of balanced?"

 

No.

 

The "balance" in "balanced" refers to impedances. Specifically the impedance of the non-inverting side with respect to ground and the impedance of the inverting side with respect to ground. These impedances being matched is critical if maximum common-mode rejection is to be achieved.

 

The Wikipedia article is about push-pull, which may be balanced or single-ended. For example the output stage of solid state amplifiers are typically what's called "complimentary push-pull" meaning that the output stage is comprised of N-type transistors and P-type transistors, but unless the amplifier is a bridged amplifier, the output is not balanced.

 

 

Quote:

It appears that the Balanced Ultra Desktop Amp is a type of push-pull ( analog case ).

 

It's a bridged amplifier so yes, it's technically both "balanced" and "push-pull," but not differential.

 

Quote:
One of the best ways to reduce noise is by using a differential amplifier.

 

Yes, but balanced headphone amps were never really promoted along those lines. It was the amplifier's output that was the focus of attention.

 

se

post #108 of 120
Quote:
Originally Posted by Steve Eddy View Post

 

No.

 

The "balance" in "balanced" refers to impedances. Specifically the impedance of the non-inverting side with respect to ground and the impedance of the inverting side with respect to ground. These impedances being matched is critical if maximum common-mode rejection is to be achieved.

 

The Wikipedia article is about push-pull, which may be balanced or single-ended. For example the output stage of solid state amplifiers are typically what's called "complimentary push-pull" meaning that the output stage is comprised of N-type transistors and P-type transistors, but unless the amplifier is a bridged amplifier, the output is not balanced.

 

 

 

It's a bridged amplifier so yes, it's technically both "balanced" and "push-pull," but not differential.

 

 

Yes, but balanced headphone amps were never really promoted along those lines. It was the amplifier's output that was the focus of attention.

 

se

 

Because it's easy to double the voltage differential for a given source voltage this way, right?  That is certainly beneficial for high-output portable amps.

post #109 of 120
Quote:
Originally Posted by BlackbeardBen View Post

 

Because it's easy to double the voltage differential for a given source voltage this way, right?  That is certainly beneficial for high-output portable amps.

 

Yes, it is of some benefit when you're dealing with low voltage battery supplies (this was done with car audio amps back in the day before switchmode power supplies started being used). Barring that however, it's a simple matter to just increase the supply voltage in AC powered amps.

 

se

post #110 of 120

I conducted more tests using balanced vs unbalanced, I no longer hear significant if any differences.  I presume I must have been under the influence of wanting it to sound different or I may have biased my results by not noticing the increase in volume.  Running more tests showed me that there is no audible difference that I can tell.

 

The tests I conducted were with a single ended headphone.

post #111 of 120

I also did extensive testing with a pair of Denon AH-D5000 headphones cabled with balanced XLR cables.  They have an XLR to TRS adapter so I can easily switch between balanced and single ended termination.  I heard no increases in sound quality be it quickness, bass impact, or frequency extension in balanced mode.  There is, of course, a 6-10dB increase in gain which I would imagine be great for Orthos or other headphones with sensitivities below 95dB/mW.

post #112 of 120

I've read through this thread and (think I) have grasped the following:

 

Balanced, when used in reference to headphone amps, is a misnomer. However, there are benefits to these so called balanced headphone amps because they prevent noise cross talk between the two signal sides of the headphones. This noise arises because of the way a single 1/4" jack plug works.

 

This noise cross talk is commonly prevented by having separate connections usually a pair of 3 pin XLR connectors, or perhaps a single 4 pin XLR, or two 1/4" jacks.

 

So, in order to prevent this noise cross talk, there is no need to have a pair of bridged amps (as in the Headroom Blockhead, which I have). A single amp with either of the three type of outputs mentioned would suffice.

 

Is this all correct?

 

There remains a couple of questions please.

 

Firstly, is this noise cross talk significant? Does it really 'muddy the stereo presentation' as the Blockhead manual says?

 

Secondly, is there still an advantage in having a pair of bridged amps (the Blockhead apparently has separate power supplies and electronics for each of the four channels) or, would one amp with the same total power suffice?


Edited by Hipper - 4/13/13 at 5:15am
post #113 of 120

1/4" TRS can have 10 milliOhm or more contact R, 1/8" 100 milliOhm

 

for 1/4", 32 Ohms the crosstalk with ~ 10 milliOhm common gnd return contact R is ~ -70 dB - not likely audible, open/semi open cans certainly have more air path crosstalk, bone conduction may give more crosstalk with iem

 

few can hear a Sousa March recorded 60 dB below a Brahms lullaby AB/X

 

may be able to hear a loud test signal's 1/8" TRS common gnd crosstalk with the one "off" channel iem at a time in just one ear, the other channel's iem with the signal under a pillow... 

 

 

with simple direct miced music, performers together in a real space, there would never be that much separation in the recorded signal

 

for Stereo LP, phono industry tests suggested better than ~25 dB separation was fine - even $K cartridges seldom say anything more specific than "better than 30 dB" separation

 

 

so claims that it "muddys the sound" are implausible - but it does make the claims of -100 dB crosstalk measured inside the amp rather pointless to any user with TRS connector

 

 

when I suggest 4-pin "balanced cable" connection over TRS I am only "following the numbers" as to purported performance, reasoning given by the "balanced" fanboys  - not suggesting anything will be audible


Edited by jcx - 4/13/13 at 9:25am
post #114 of 120
Thread Starter 
Quote:
Originally Posted by Hipper View Post

Secondly, is there still an advantage in having a pair of bridged amps (the Blockhead apparently has separate power supplies and electronics for each of the four channels) or, would one amp with the same total power suffice?

That is why I started this thread smily_headphones1.gif

 

I see no advantage to the bridged design over a comparable conventional amp and there are in fact disadvantages, namely increased cost and noise/distortion (twice the component count) though the latter is almost certainly negligible. Primarily it is a cost/performance issue. Having said that, I recently had the pleasure of listening to Bryston's new BHA-1 headphone amp which is bridged when listening in balanced mode (I listened to it single ended). At $1395 this amp is IMO within spitting distance of the best I have ever heard (my personal favorite is the Cavalli at triple the price - this was the original liquid fire, I have not heard the new one). So you can indeed design a superlative "balanced" amp for a reasonable price.

 

The "balanced" (bridged) designs seem to have originally arisen in an attempt to increase performance without requiring a board redesign, and it appears that Headroom actually started this off. Later they became popular and new designs came out that were designed from the start to be bridged.


Edited by sbradley02 - 4/14/13 at 8:36am
post #115 of 120

Twice the voltage swing as compared to single ended makes for a more dynamic experience.

post #116 of 120
Quote:
Originally Posted by wink View Post

Twice the voltage swing as compared to single ended makes for a more dynamic experience.

...only if played near clipping where the single ended maximum voltage is insufficient. If you don't use the extra voltage, it makes no difference.  I would advance that most headphone amps of either design operate nowhere near clipping, even at loud volumes.

post #117 of 120
Thread Starter 
Quote:
Originally Posted by jaddie View Post

...only if played near clipping where the single ended maximum voltage is insufficient. If you don't use the extra voltage, it makes no difference.  I would advance that most headphone amps of either design operate nowhere near clipping, even at loud volumes.


Yep.

Lets look at the worst case. A HiFiman HE-6 requires around 10V per supply rail (assuming bipolar) for full output which is trivial without using bridging.

This is far and away one of the most inefficient headphones. Most others will require much less voltage.

post #118 of 120
Quote:
Originally Posted by sbradley02 View Post

That is why I started this thread smily_headphones1.gif

 

I see no advantage to the bridged design over a comparable conventional amp and there are in fact disadvantages, namely increased cost and noise/distortion (twice the component count) though the latter is almost certainly negligible.

 

And look at Cavalli's new $6k+ balanced amplifier. Haaaa. Yikes. 

post #119 of 120
Thread Starter 
Quote:
Originally Posted by paradoxper View Post

And look at Cavalli's new $6k+ balanced amplifier. Haaaa. Yikes. 


The Liquid Fire was not balanced, which is the one I heard. It was still crazy expensive at $3250.

I would need to A-B it directly with the Bryston to see if it is substantially better, or whether my audio memory is faulty.

The Bryston has 6 amplifier sections, two for single ended, four for balanced. Think how much less expensive it would be if it came in a single ended only version.

post #120 of 120
Quote:
Originally Posted by wink View Post

Twice the voltage swing as compared to single ended makes for a more dynamic experience.

 

"Twice the voltage swing as compared to single ended" is rather meaningless and even misleading.

 

A given "balanced" amp won't necessarily have twice the voltage swing as a given single-ended amp. Both types of amps can have whatever voltage swing you want to design them to achieve. There are "balanced" amps that have greater voltage swing than some single-ended amps and single-ended amps that have greater voltage swing than some "balanced" amps. And as jaddie points out, you're not going to inherently achieve any greater dynamic experience by going balanced. It all depends on the specific amplifiers in question.

 

se

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