John Curl's Blowtorch preamplifier part II - Page 2383 - diyAudio
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Old 9th June 2012, 12:12 AM   #23821
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Originally Posted by jam View Post
Wavebourn,

...................you know it.
Is that thing FDA approved?

se
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Old 9th June 2012, 12:20 AM   #23822
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Almost worth going balanced, no?
John,

On going balanced; I don't see the advantage of fully balanced over 1 lead tied to signal ground and 1 hot (1HC for shorthand), but I stand to be corrected. That is exactly why I am floating this idea, to falsify it if wrong before I start soldering something together.

There are a couple of disadvantages to fully balanced as I see it. The first is that you need extra electronics or transformers to generate a balanced signal and to subsequently bring it back to an unbalanced signal in the next stage. Closely related to that is that common mode rejection is never perfect. With an unbalanced signal with one hot and one cold line within a seperately grounded shield, my thinking is that you don't need all this and common mode rejection is definitionally perfect.

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It sounds like a reasonable idea, but it doesn't eliminate induction coupled ground currents, just IR. Might be good enough for almost everybody..

jn
I am just wondering how fully balanced and 1HC might differ in this respect, but can't crack the nut.

vac
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Old 9th June 2012, 12:39 AM   #23823
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Is that thing FDA approved?
I think it is an alien food supplement, no need for approval.
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Old 9th June 2012, 01:13 AM   #23824
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I think it is an alien food supplement, no need for approval.
AH HA! So all these years the aliens have only been trying to FEED US! You'd think by now they'd have figured out that food goes at the OTHER end.

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Old 9th June 2012, 01:15 AM   #23825
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AH HA! So all these years the aliens have only been trying to FEED US! You'd think by now they'd have figured out that food goes at the OTHER end.
Very probably! Like our cat still can't figure out that she brings us wrong food!
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Old 9th June 2012, 01:29 AM   #23826
bcarso is offline bcarso  United States
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Originally Posted by vacuphile View Post
John,

On going balanced; I don't see the advantage of fully balanced over 1 lead tied to signal ground and 1 hot (1HC for shorthand), but I stand to be corrected. That is exactly why I am floating this idea, to falsify it if wrong before I start soldering something together.

There are a couple of disadvantages to fully balanced as I see it. The first is that you need extra electronics or transformers to generate a balanced signal and to subsequently bring it back to an unbalanced signal in the next stage. Closely related to that is that common mode rejection is never perfect. With an unbalanced signal with one hot and one cold line within a seperately grounded shield, my thinking is that you don't need all this and common mode rejection is definitionally perfect.



I am just wondering how fully balanced and 1HC might differ in this respect, but can't crack the nut.

vac
Many transducers are inherently balanced to begin with (e.g. phono cartridges, loudspeakers) but we alter that for convenience. And the necessary duplication associated with balanced requires more parts for the same ideal (interference-free) noise performance.

The difference in interference rejection between true balanced and something short of that pertains to the sensitivity of each line to external disturbances; if the impedances of each conductor are not the same, rejection of various noise sources will not be as good.

And it needs to be reiterated for some readers, that "balanced" is not equal and opposite polarity signals on each signal conductor, but rather equal impedances to common. Thus "pseudo-balanced", with one conductor at the source carrying the signal voltage and the other conductor nominally at zero signal, but with the same impedance as the first, can work very well indeed. For a given available power supply voltage, driving the two conductors with equal magnitude and opposite polarity signals can be an advantage for dynamic range, but does not per se improve the rejection of common-mode disturbances.
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Old 9th June 2012, 01:48 AM   #23827
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Like our cat still can't figure out that she brings us wrong food!
But it is we who bring her the wrong food - she'd really prefer something mouse flavored. Yum!

And I always enjoy a little love offering left on the bed, sometimes with the head thoughtfully removed.

Chris
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Old 9th June 2012, 01:53 AM   #23828
SY is offline SY  United States
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Exactly, Brad. As John likes to say, we're talking ultimate performance, so the parts count to do balanced is not as relevant. Input transformers can have incredibly good CMR well into the ultrasonic, and to boot they give galvanic isolation and reasonable bandwidth limiting. Like John, I was pretty down on them due to experience with older and lesser examples, but once Steve convinced me to try something modern and high quality, I never went back.
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Old 9th June 2012, 01:58 AM   #23829
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The difference in interference rejection between true balanced and something short of that pertains to the sensitivity of each line to external disturbances; if the impedances of each conductor are not the same, rejection of various noise sources will not be as good.
I had bi-metal lines 300 kM long going on poles on open air when worked as a lead engineer of railway radio and electronics support. They carried both AF and RF signals, no hum until asymmetry happens (bad contact, dirty insulators).




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But it is we who bring her the wrong food - she'd really prefer something mouse flavored. Yum!

And I always enjoy a little love offering left on the bed, sometimes with the head thoughtfully removed.
You are right Chris. It is we who don't understand their needs and language. (Russian text reads, "Most significant things are not things")

Click the image to open in full size.
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Old 9th June 2012, 02:02 AM   #23830
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Transformers are undeniably great, especially when there's uncertainty about the d.c. potentials in a system. Whitlock told me that Jensen was almost moribund (maybe not his exact term, but let's say not growing by leaps and bounds) until the rise of home theater and the proliferation of satellite feeds, with mandated hard grounding for lightning protection etc. and almost certain ground problems for everything else. So Jensen had a range of solutions at various signal bandwidths certain to allow correction of the problems.
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