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Balanced output amps

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    Posted: 24 Apr 2019 at 9:23pm
If this as already been asked a million times I’m sorry. When looking on YouTube to see what headphones are out there it seems that a lot of folk are raving about balanced amps and headphones.  Is there any technical reason they are more superior to a single ended amp? or is it a case of hype. I’m not thinking of selling my solo I’m just curious about the subject. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 24 Apr 2019 at 10:17pm
Hype
Not simple enough for Google-Bot to understand...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 2019 at 7:11am
I feel I must qualify my remark. Balanced audio belongs to the domain of professionals where it is advantageous in preventing noise, but another use is to idiot-proof against grounding issues, especially in broadcast situations, where in my experience there can be idiots.

So, assuming we're not idiots, that leaves noise. And not being idiots (?) we understand that in professional uses (that's real professional and not the youth bedroom-disco type of "professional") there can be hundreds of feet of interconnect cables, and these pose a noise pick-up problem.

By driving the source end of the cable with an impedance of 600 ohms, which is 300 ohms per phase, and terminating it at the other end by 600 ohms across phases, there is 6dB signal - and source noise - loss. Then an unbalance circuit takes the anti-phase and inverts it using an "in-amp" such that any noise common to both phases is cancelled.

Do headphones have this unbalance circuit? Obviously not, so they're not going to benefit from any noise cancellation. Do headphones have 600 ohm impedance? Some used to, but mainly they're anything from 5 ohms to 300 ohms these days.

So I guess it must be about grounding? It seems obvious these people believe the ground return somehow causes intermodulation between channels.

Where could this appear? Well, it could appear because of a shared return, but for the fact that all the headphones I've had use separate wires (two pairs), and the only commoned bit is in the jack plug where the two separate returns join.

Perhaps the headphone amp ground isn't "solid" enough? Could it be "pulling current"? Just how much current does a headphone need? When loud enough for ear damage it will only be a hundred or so milliamps, but mainly in the tens of milliamps. A 4mm wide PCB track can do a few amps without becoming noticeably resistive, and if kept short and the ground "Mecca" is done properly, the percentage of intermodulation will so low as to be inaudible.

Now, I suppose a badly designed headphone amp might benefit by separating the grounds, which is where you find them fitted with a 4 pole socket, and that means you have the chore of fitting a different plug on your headphones, but come-on, that's a crutch to support a design wannabe!

Perhaps the other reason for "balanced headphone amplifiers" is that any wannabe designer can obtain two car radio power amplifier chips, which tend to be bridged (he'll call them balanced) to get the required headbanging power, and which will conveniently operate on a 12 volt wall-wart. Just need a nice case?

So, having done so, he will probably be quite savvy at social networking, and at blogging, possibly understanding "black-hat" search engine optimisation (SEO), and you never know, he might have secured crowd funding. He might also have grown forum followings too.

All he then needs is to get people to listen to it, and it will sound different I assure you. And obviously in hi-fi different always means better??

And even Sennheiser jumped on that bandwaggon, forsaking the Solo's they used to use at shows.

Specification-wise they may exhibit fantastic THD and noise measurements, but it seems we have forgotten, never knew, or mixed up our minds so much that we have forgotten the basics for good sound.

You only need search "amplifier" to be innundated with contradictory results. Should we chase after the holy slipper, or the holy gourd? ("Life of Brian" Monty Python)

It is what I would term "addled fandom", to which there seems to be no antidote.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kamo1974 Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 2019 at 7:51pm
Thank you Graham. This was the sort of insight and well founded response I was looking for. It’s not very often you can get a response from a fully fledged engineer with your track record.

As most things in Hifi the BS marketeers and snake oil sellers and I include big names in this(not you btw) just jump on the band wagon. A new way of selling stuff and then try to peddle it as the best new thing. Again this is not new, but it is refreshing to be able to ask a question on here and get what I consider a true answer.

The industry are seemingly blurring the lines between true pro audio and home stuff if that makes sense. With the rise in studio monitors becoming more prolific in the main steam mags and forums. Look at the rise of ATC on forums for example. I’m not having a pop at this side of audio, in fact I would like a pair if my pockets were deep enough. Again I would love a studer tape and a real mixing desk.  

My guess would be a real pro set up would be at odds what my inner audiophile would be happy withSmile
 

 
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