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Old 28th January 2013, 06:01 PM   #11
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Originally Posted by jcx View Post
balanced audio interface between source and amp is a possibly independent issue from “balanced”/bridged headphone amplification/driving

I believe most professional equipment using balanced signal interface converts to single ended internally

many “balanced” headphone amps are in fact just 2 identical, separate amps for the +,- balanced signal inputs – which means any common mode on the input is amplified, eats into the output Vswing
while a “proper” balanced receiver actually removes the common mode V
dynamic headphone driver's basically don't care about anything but the difference V at their terminals so there is rejection of the (amplified) common mode in their audio output

rewiring headphones for “balanced” cables, bridged drive is somewhat faddish but separating the R,L driver gnds does offer technical improvement in common impedance crosstalk over TRS common gnd
but you don't need the bridged drive to get most of the advantage of the separated R,L driver connectors – just attention to the amp's internal gnding fine details

bridged drive can give even harmonic distortion cancellation – where it is reproducible enough between the +,- amplifier devices
since even harmonics are often considered less audibly objectional the benefit is questionable

and a proper balanced receiver input, driving a single ended amp can be technically way better than estimates of audibilty
the technical differences with a “balanced”/bridged drive amp can easily be in implementation details rather than fundamental topology advantages
I agree.
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Old 28th January 2013, 06:11 PM   #12
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Originally Posted by Neutrality View Post
Well, if you have a simple SE build, any noise the input cabling picks up will get amplified and end up in your headphones as, well, noise.
That depends on your design. You could, for instance, add a good quality 1:1 transformer at the input. That would offer you outstanding common-mode rejection even if you feed it from an unbalanced source (and it can just as easily accept a balanced source). In addition, you get ground isolation which can help reduce noise due to ground loops.

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Old 28th January 2013, 06:19 PM   #13
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Originally Posted by Steve Eddy View Post
That depends on your design. You could, for instance, add a good quality 1:1 transformer at the input. That would offer you outstanding common-mode rejection even if you feed it from an unbalanced source (and it can just as easily accept a balanced source). In addition, you get ground isolation which can help reduce noise due to ground loops.

se
That is an option.

But when you do not have issues with noise(I don't), well, then there is nothing to fix.

But it is a simple solution for those that do have noise issues.
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Old 29th January 2013, 04:40 AM   #14
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Originally Posted by Neutrality View Post
That is an option.

But when you do not have issues with noise(I don't), well, then there is nothing to fix.

But it is a simple solution for those that do have noise issues.
Even without any problems to "fix," I've always been fond of using an input transformer on my stuff.

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Old 29th January 2013, 04:45 AM   #15
cotdt is offline cotdt  United States
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Balanced/bridged would help in driving hard-to-drive orthostatic headphones where a lot of voltage swing is needed.
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Old 29th January 2013, 05:27 AM   #16
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Balanced/bridged would help in driving hard-to-drive orthostatic headphones where a lot of voltage swing is needed.
That would help if you had a limited supply voltage to deal with like a battery supply, but with an AC supply it's easy enough to choose whatever voltage you need.

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Old 30th January 2013, 09:54 AM   #17
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Just how good is the CMRR of a typical dynamic headphone transducer anyway? Assuming it should be pretty damn good.

Last edited by chris719; 30th January 2013 at 09:57 AM.
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Old 30th January 2013, 03:43 PM   #18
Telstar is offline Telstar  Italy
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Interesting topic.
While I have no advice to offer, I'd say to the OP to build it, then try with a transformer or an alternative differential input to check if you hear an improvement or not.
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Old 6th February 2013, 08:46 PM   #19
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@6L6
Beautiful photo essay and your accompanying write-up has some good tips as well.
I've been thinking of building an O2 myself and this instruction does make the process a lot less intimidating.
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Old 31st March 2013, 12:54 AM   #20
Wolfsin is offline Wolfsin  United States
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Hi Neutrality,

I find your thinking convincing, probably because it mirrors my own. I started building dual mono (discrete then LME49600 buffered), feeding them a balanced signal, and feeding to each side of modified cabling across HD600 cans. This result bettered the Creek OBH-11 I had been using. I tweaked the power supplies but the big leap came when I built 'the Wire' BAL-BAL.

I wish I could have skipped a few of the intermediate steps and gone straight to 'the wire'. If the HD600's were less of a hog the improvements might have been less apparent, dunno. I heard opc plans a rerun. recommended.
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