[EliasGwinn]

Tyll,

Thank you for your reply. I appreciate you taking the time to discuss this technology. Balanced headphones has seen quite a boost of popularity recently. I've read your website's articles on this, as well as some additional material around the internet. So far, I have to say that I'm not convinced that this technology is actually advantageous over the standard topology, but I am very open-minded about discussing and analyzing it for the sake of advancement of audio. In a way, I hope it is true...I hope balanced is better because that means we are moving in the right direction as an audio community, and that means better listening for everyone !! But I think it is important to find out for sure, as I'm sure you can understand.

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Originally Posted by Tyll Hertsens /img/forum/go_quote.gif 1) Getting rid of the common ground connection in the headphones, which lowers crosstalk.

This can be a problem, for sure, if the negative driver terminals are shorted. However, most high-quality headphones aren't wired as the diagram on your website indicates. Most headphone cables don't share a common ground until the plug (in the chassis). In the article on your website, it indicates that they are common at the Y or at the drivers themselves. In fact, they are not common until the chassis. Most headphones don't share a return path conductor. The difference is that the inherent resistance of the cable from the drivers to the common plane provide enough isolation from any sort of cross-fed voltage that might be present on the common ground. This is why circuit-board layout is such an important (and often overlooked) aspect of the performance.

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Originally Posted by Tyll Hertsens /img/forum/go_quote.gif Originally Posted by Tyll Hertsens 2) Doubling of slew rate.

I am interested to know the slew-rate of the balanced vs. unbalanced configuration. The BUF634 has a slew-rate of 2000V per microsecond. Its very hard to believe that any audio can even come close to this limit. I can't imagine why doubling this limit would be valuable.

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Originally Posted by Tyll Hertsens /img/forum/go_quote.gif Originally Posted by Tyll Hertsens 3) Doubling of the wattage delivered to the headphone drivers.

Again, I can't imagine a headphone amp that needs the assistance of doubled wattage. If we were reaching a 50% point of a driver amp, then we may be compromising the performance. But do we really reach that point?

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Originally Posted by Tyll Hertsens /img/forum/go_quote.gif Originally Posted by Tyll Hertsens 4) Cancellation of some of the distortion products of the amp.

I'm not sure I understand how this is achieved. Forgive me, but can you please elaborate on this a little bit?

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Originally Posted by Tyll Hertsens /img/forum/go_quote.gif Originally Posted by Tyll Hertsens There are also some things that may be worse. 1) Because you are only driving half the load with each side of the balanced amp (there is a virtual ground point half way into the driver coil) the effective impedance each amp is driving is halved, resulting in a halving of the damping factor each amp sees.

This is the reason I haven't been able to get excited over this topology. This is a major downside, as it is the usually the limiting factor of how well an amp drives a set of drivers. Especially when dealing with low impedance headphones like the Shure E500's.

If we could find a new topology to lower the output impedance below 0.1 ohm, then I would be getting very excited .

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Originally Posted by Tyll Hertsens /img/forum/go_quote.gif Originally Posted by Tyll Hertsens 2) It is critical the the inverted and non-inverted channels are matched to realize item 4) above; if not, you can actually create more problems than you solve.

I can't wait till parts start achieving ideal specs...

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Originally Posted by Tyll Hertsens /img/forum/go_quote.gif Originally Posted by Tyll Hertsens For the most part, achieving these results is a matter of channel matching pairs of highly linear amplifiers. Other than that it's a pretty "brute force" method of achieving improved performance. That's essentially another advantage of this method: Simply doubling the amount of audio electronics of a known good design double many of the performance characteristics. Getting double the objective performance otherwise would take significant changes in circuit topology and componant performance. In other words, you can take an existing design and double its performance simply by doubling the number of circuits and doing some critical matching.

With all due respect, I have to disagree with this statement. If they were in parallel driving a single side, this can be true. However, this is not true when the components are in series - as is the case with the balanced headphone configuration. For instance, you're now adding twice the noise of each amp. Also, each amp sees half of the load it would normally see, which results in more distortion per amp.

Quote:

Originally Posted by Tyll Hertsens /img/forum/go_quote.gif Originally Posted by Tyll Hertsens I'll check into the actual overall slew rate numbers next week, but what ever it is single-ended, it's double when driven differentially.

Again, thank you very much for engaging in this dialog. Engineers such as yourself who discuss and analyze for the sake of the state-of-the-art should be appreciated and applauded.

Thanks,
Elias

 

[noseallinit]

Quote:

Originally Posted by Tyll Hertsens /img/forum/go_quote.gif Thanks! That's exactly what I feel. One of the problems I sometimes have is that once the prototypes show up on my desk I can feel my drive to complete the process for indroducing products decrease. After all, I've got mine. But fear not, it's comming. As assurance I'll offer that I've continued to redesign the speaker stands so that they look even cooler. That's assurance because now I want the new version on my desk!

your the best Tyll!

so glad that the prototypes leave your desk and HeadRoom keeps turning out killer products for us to enjoy! q:O)

 

[Tyll Hertsens]

Quote:

Originally Posted by EliasGwinn /img/forum/go_quote.gif However, most high-quality headphones aren't wired as the diagram on your website indicates. .... The difference is that the inherent resistance of the cable from the drivers to the common plane provide enough isolation from any sort of cross-fed voltage that might be present on the common ground. This is why circuit-board layout is such an important (and often overlooked) aspect of the performance.

At this point many premium cans indeed do not common the return until you get to the plug. However, many still do. It doesn't matter too much, because in my view, the most likely point where cross talk will occur is through the contact resistance of the headphone plug/jack connection.

Quote:

I am interested to know the slew-rate of the balanced vs. unbalanced configuration. The BUF634 has a slew-rate of 2000V per microsecond. Its very hard to believe that any audio can even come close to this limit. I can't imagine why doubling this limit would be valuable.

You know, your point is well taken here: you wouldn't think that improving the slew rate far past the bandwidth limits of audio would do anything. Frankly, I don't know why (other than generally) balanced outperforms SE so significantly. I know it's likely some part of the various things I mentioned, but I don't know how much each aspect contributes to the end result. All I do know is that we can run balanced and single-ended cans of the same amp using identical circuits, and the difference is clear ... not only to myself but to the vast majority of folks who've tried it.

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(Re: distortion reduction) I'm not sure I understand how this is achieved. Forgive me, but can you please elaborate on this a little bit?

If you look at the gain curve (Load line?, transfer function) of a linear amp it should ideally be a straight line. But, of course, it's not. (I'm trying to write this so others can read it, I appologies if I'm saying things that you, as an engineer would totally know.) Tube amps typically have a transfer function that has a simple curve in one direction---usually the gain decreases as voltage increases. Solid state amps usually are straighter lines, but compress at the extremes somewhat. The monotonic curve of a tube amp creates even order harmonic distortions, and the symetric (changes at both extreemes) curve of a ss amp creates odd harmonic distortions.

In a balanced amp, the two-part signal goes through the amps, one inverted and one not. If you take a moment in time when the signal is very high in the positive direction, the non-inverted channel will be a high positive voltage, but the inverted channel will be a low voltage. So the drive signal is using two different parts of the gain curve of the two identical amps any time it's not zero.

The result is that any asymetries of the load line are averaged out to some extent because the load is being driven by signals the are using two different parts of the gain curve of the drive amps. If the amps gain curves are perfectly symetrical around the zero point it wouldn't make any difference---and to a large extent, ss amps are---but certainly any even order harmonic is not, and certainly even ss amps are not perfectly symetrical.

Quote:

Again, I can't imagine a headphone amp that needs the assistance of doubled wattage. .... This is the reason I haven't been able to get excited over this topology. This is a major downside, as it is the usually the limiting factor of how well an amp drives a set of drivers. Especially when dealing with low impedance headphones like the Shure E500's. If we could find a new topology to lower the output impedance below 0.1 ohm, then I would be getting very excited .

Getting a low output impedance is a bit of a trick. It's actually pretty easy to get an amp to have below 1 Ohm output impedance. The problem is protecting the amp against the dead short that sometimes happens if the headphone plug is not properly inserted. We have battled this issue somewhat and have accepted a somewhat higher output impedance than ideal in order to insure that people don't blow up their amps when they plug in their cans when the amp is hot.

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I can't wait till parts start achieving ideal specs...

Yeah ... and I'd like a naked Haagendaas Godess to be at my side 24/7 to spoon me rum raisen at my demand.

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However, this is not true when the components are in series - as is the case with the balanced headphone configuration. For instance, you're now adding twice the noise of each amp. Also, each amp sees half of the load it would normally see, which results in more distortion per amp.

Yup. I agree, those are some additional issues. All I can say again is that the proof is in the pudding: When done well, our experience is that balanced drive delivers astonishing clarity.

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Again, thank you very much for engaging in this dialog. Engineers such as yourself who discuss and analyze for the sake of the state-of-the-art should be appreciated and applauded.

No ... thank you. I'm not an engineer; I'm a marketing geek that understands a lot of this stuff at a basic level. Joe is our engineer, and and I talk here and double check what I say with him when I'm uncertain of things.

 

[vcoheda]

interesting dialogue!

 

[Tyll Hertsens]

Quote:

Originally Posted by vcoheda /img/forum/go_quote.gif interesting dialogue!

Indeed! and really much more interesting as you get far deeper into the technicallities of the situation relative to all the trade-offs --- like the value proposition versus ultimate performance; ICs v. discrete; reliability v performance; etc. Saddly, those are conversations that are to long, complicated, and commercially sensitive to have here.

I kind of wish we could have gotten into some of those issues at the amp makers panel at HeadFest. But even there it would have been difficult; not to mention it gets very quickly over even my head. And if you think amp topologies are complex, you should start having conversations about digital to analog conversion upsampling and DSP schemes. That's some esoteric stuff!

 

[EliasGwinn]

Tyll,

Do you think that, perhaps, the balanced headphone configuration 'sounds' better because it introduces more flattering distortion? The reason I propose this question is because I would never question someones opinion of quality of sound. The perception of sound is a very personal, and very real experience. This is why tube amps are popular - they introduce a very flattering distortion.

Everything commonly known about electrical design techniques would indicate the balanced headphone configuration (both leads of the headphone driven actively) will distort more then with one lead being driven. This is very well known with power amps. That is, power amps will experience more distortion if they are driven in bridged mode. This configuration is exactly similar to the balanced headphone configuration.

So, what I'm trying to say is... I can not and would not argue with a "proof is in the pudding" claim of the balanced headphones sounding better. I'm merely suggesting that this is perhaps due to the balanced (bridged) headphones introducing certain resonants that make them sound 'fuller'.

Any thoughts?

Thanks,
Elias

 

[thrice]

Quote:

Originally Posted by Tyll Hertsens /img/forum/go_quote.gif Getting a low output impedance is a bit of a trick. It's actually pretty easy to get an amp to have below 1 Ohm output impedance. The problem is protecting the amp against the dead short that sometimes happens if the headphone plug is not properly inserted. We have battled this issue somewhat and have accepted a somewhat higher output impedance than ideal in order to insure that people don't blow up their amps when they plug in their cans when the amp is hot.

[soapbox]Now if we can convince headphone manufacturers (and amp manufacturer (nudge, nudge) to use 4 pin xlr plugs, this wouldn't be an issue (except with portable amps....I know. Perhaps a mini 4-pin xlr?[/soapbox]

 

[jpelg]

Sounds like a lot of complicated talk about getting a little driver to push air in a fairly small, relatively (if not completely) enclosed space around my ear

.

I, personally, don't hear a significant benefit of balanced headphone amps, other than maybe being louder vs. SE. But then again balanced source outputs are usually at a higher voltage, so that part makes sense. But more "refined" sound? Nope.

 

[noseallinit]

I'm a bit confused on what Elias is getting at.

what is the difference in headphones being driven balanced as compared to other studio equipment such as monitors? much of the studio equipment use balanced connections.

all of Benchmarks equipment that I have looked at has balanced inputs and outputs on them. why do they use balanced connections on their equipment?

what is the difference here about doing it with headphones that I am not getting?

 

[Tyll Hertsens]

Quote:

Originally Posted by EliasGwinn /img/forum/go_quote.gif Do you think that, perhaps, the balanced headphone configuration 'sounds' better because it introduces more flattering distortion?

Actually, because it mostly cancels non-symetrical distortion (theoretically the even stuff) and doesn't do much to the perfectly symetrical odd harmonic, you would think it would strip some euphony and actually sound a little worse. No, I think distortion is a secondary thing in term of sound quality improvements. I think it's mostly getting rid of the common ground; then that the slew rate increases; then (given the amps have a low enough output impedance to drive the halved load easilty) the greater power authority given the driver is being driven by two amps instead of one. After that, who knows, kinda.

I want to mention here that I think that there's a lot to be said for true single ended/class-A designs, and I think many of the advantages of these designs may be cluttered up in a balanced differential drive scheme. So, I do not advocate balanced differential drive as a lone path sonic improvements. Mearly, that when designing linear amplifiers (meaning the goal of the design is a straightwire with gain; not talking about euphonically designed amps) it can act as a means to significantly improve the performance of a given circuit topology at the price of doubgling and matching the circuits.

Quote:

Everything commonly known about electrical design techniques would indicate the balanced headphone configuration (both leads of the headphone driven actively) will distort more then with one lead being driven. This is very well known with power amps. That is, power amps will experience more distortion if they are driven in bridged mode. This configuration is exactly similar to the balanced headphone configuration.

You know, I'm going to have to play my "I'm not an engineer" card, and ask you for some help. I didn't think brigding a power amp was quite the same as turning it into a differential drive amp. BUt I must admit that I've never looked into it. Would you give us a little primmer on how a solid state, class a/b, complementry pair output amplifier is switched between a pair of single ended amps into a differential drive amp. And then, because I've never heard the claim or the logic behind your statement, could you tell me how a bridged power amp developes the non-linearities to produce more distortion in that configureation.

Thanks!

 

[KenW]

Quote:

Originally Posted by nkoulban /img/forum/go_quote.gif Out of curiosity I auditioned a Lavry DA10 working balanced through the Desktop balanced to see how the internal DAC compares... guess what... it sounds virtually the same. The Lavry is a killer DAC for sure and it manages to sound a bit more open and airy and maybe a fraction more detail... that's it in this application. Hardly worth spending $1K to get very incremental benefits. The more I listen to the Headroom Balanced Desktop the more respect I have for it.

It came pretty darned close to my Stello as well....so close that the Stello now has a new home/owner.

With each passing day, I become more and more impressed by this little gem. To wrap an amp and dac into such a small package AND have it perform at the level that it does is truly quite the accomplishment....oh and all those connection options... how did they get all that in there??

 

[Tyll Hertsens]

Quote:

Originally Posted by KenW /img/forum/go_quote.gif ... how did they get all that in there??

Corporate obsessive/compulsive disorder.

 

[KenW]

Quote:

Originally Posted by Tyll Hertsens /img/forum/go_quote.gif Corporate obsessive/compulsive disorder.

Speaking for all your customers/admirers...I hope you don't find a cure! This is one IMPRESSIVE piece of gear!

 

[Tyll Hertsens]

Quote:

Originally Posted by KenW /img/forum/go_quote.gif ...I hope you don't find a cure!

Fear not, it's terminal.

 

[n_maher]

Yeah, from the pictures we all saw from the National Meet Tyll isn't exactly showing signs of slowing down. Max DAC in a Micro enclosure anyone?