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
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.
se
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!
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.
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
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.
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).
You are right Chris. It is we who don't understand their needs and language. (Russian text reads, "Most significant things are not things")
An externally hosted image should be here but it was not working when we last tested it.
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.
Very probably! Like our cat still can't figure out that she brings us wrong food!
Or our dog who thinks the cats' litter box is an hors d'oeuvres tray.
se
Or our dog who thinks the cats' litter box is an hors d'oeuvres tray.
se
Ha ha we have the same problem.
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.
se
Not from what one hears national representatives say.....irrespective of country!
I googled for IEEE Std.1050 and I found the 1989 edition in pdf.
Well written and carefully worded document. Thanks jneutron for pointing to it.
In there, I read something (one of the things at least that) I didn’t know. That low – impedance circuits are less susceptible to capacitive coupled noise and crosstalk . This may answer my own question:
The circuits inside audio ICs are relative low impedance (Vac/Iac). Furthermore, the“de” part of the capacitive coupling equation I=C de/dt is fairly low (*).
On the other hand these low impedance circuits are more susceptible to inductive coupling and the “di” part of the inductive coupling equation E=M di/dt becomes significant, thus your emphasis specifically on inductive coupling
makes sense to me now.
But for this question I haven’t been honored an answer yet
George
(*) May be this is the reason that high package density modern CPUs are designed for lower voltage supply than the previous generation CPUs which were less densely packaged.
Well written and carefully worded document. Thanks jneutron for pointing to it.
In there, I read something (one of the things at least that) I didn’t know. That low – impedance circuits are less susceptible to capacitive coupled noise and crosstalk . This may answer my own question:
As I read it, you target the problem at the bonding wires and pads. That’s in agreement with Scott words.
This I find strange. I mean how all the routing within each layer and the stacked layers between them end up less troublesome than the bonding wires.
The circuits inside audio ICs are relative low impedance (Vac/Iac). Furthermore, the“de” part of the capacitive coupling equation I=C de/dt is fairly low (*).
On the other hand these low impedance circuits are more susceptible to inductive coupling and the “di” part of the inductive coupling equation E=M di/dt becomes significant, thus your emphasis specifically on inductive coupling
makes sense to me now.
But for this question I haven’t been honored an answer yet
Scott, I hadn’t noticed your response, sorry.
Now, to exercise your patience, one more step on the ladder:
Why these “conventional methods” brake up above say 100MHz?
Is it that the conception of L/R/C can not model the reality anymore, and if so, why?
(I guess the next floor is a few more steps higher, so prepare yourself
George
(*) May be this is the reason that high package density modern CPUs are designed for lower voltage supply than the previous generation CPUs which were less densely packaged.
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The methods don't "break", but I've found it instructive to consider resonances and note just how rapidly the L's and C's of significance get very small indeed. And this is before abandoning lumped circuit elements.
We tend (or used to tend) to think of a picofarad as a small capacitance, and maybe a tenth of a microhenry a fairly small inductance. But as a resonator those two values have a frequency of resonance of about 500MHz, and if constituting the distributed L and C of a lossless transmission line, a characteristic impedance of about 316 ohms.
I recall an experimental "opamp" described some years ago that was reasonably well-behaved out to about 10GHz. The developers remarked that, despite their fears, it behaved in accordance with an analysis that didn't change in character from ones appropriate to far lower frequencies. But of course the dimensions were very small.
We tend (or used to tend) to think of a picofarad as a small capacitance, and maybe a tenth of a microhenry a fairly small inductance. But as a resonator those two values have a frequency of resonance of about 500MHz, and if constituting the distributed L and C of a lossless transmission line, a characteristic impedance of about 316 ohms.
I recall an experimental "opamp" described some years ago that was reasonably well-behaved out to about 10GHz. The developers remarked that, despite their fears, it behaved in accordance with an analysis that didn't change in character from ones appropriate to far lower frequencies. But of course the dimensions were very small.
"Conventional methods" break above the frequency when the size of the circuit begins to be a non-negligible fraction of the wavelength. The lumped LC circuit model is always an approximation of reality, but a very good approximation for sufficiently low frequencies. The wave model is always true, but unnecessarily complicated when the lumped model is good enough.
For pulse circuits substitute (approximately) 1/(rise time) for frequency - maybe there should be a 2 pi in there somewhere too.
For pulse circuits substitute (approximately) 1/(rise time) for frequency - maybe there should be a 2 pi in there somewhere too.
Ouch!
Largest dimension ~0.15 of wavelength (IEEE Std.1050)
I’ll keep these two. They match my understanding too.
Thank you both for answering (*)
George
(*) In lew of Scott. Most probably he is messing around with SY, excusing themselves they are doing some live recordings again.
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