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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 5th November 2011, 03:11 AM   #17581
ThorstenL is offline ThorstenL  Germany
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Hi,

Quote:
Originally Posted by rsdio View Post
First of all, a self-professed expert such as yourself must know that balanced has a +6 dB advantage over unbalanced. Factoring in the 3 dB noise only occurs when you combine the balanced signals into an unbalanced signal, but with Papa's SuSy, you can avoid combining the signals until the speaker. In any event, the worst case for balanced is a +3 dB signal to noise advantage. I have no idea why you would ignore the +6 dB advantage unless you're just trolling.
Well, well well. Another round of Mythbusters? Well, actually, I don't really care, so I won't bother to cover this in detail, honest.

Quote:
Originally Posted by rsdio View Post
Second of all, the PCM1704 already has this 3 dB noise penalty by nature of using two DACs internally.
Really, so you mean using two DAC's in parallel reduces SNR by 3dB?

Quote:
Originally Posted by rsdio View Post
All I ask is that they take each output to a separate pin rather than combine them internally.
Are you sure you really understand how the PCM1704 works?

Quote:
Originally Posted by rsdio View Post
There's no way according to Kirchoff's laws that they can avoid the 3 dB noise penalty simply by combining internally.
Really, I guess it is time that I take Bob Adam's advice to Scott Wurcer...

Quote:
Originally Posted by rsdio View Post
Thanks, but I don't see anything in the data sheets which says there are two DACs.
You don't? As it so happens I see one differential current output DAC for left channel and another for the right channel. Makes two DAC's in my milmaid 1 + 1 = 2 calculation, but WTFDIK.

Quote:
Originally Posted by rsdio View Post
You do realize that it is possible to design a single DAC with differential outputs, don't you?
More to the point, I even know quite a few examples.

Quote:
Originally Posted by rsdio View Post
Why can't you just ignore one of the differential outputs?
It highly depends on the DAC used and many other factors. But yes, you can do that and I have documented doing that for Audio DAC's over a decade ago.

Ciao T
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Old 5th November 2011, 03:20 AM   #17582
ThorstenL is offline ThorstenL  Germany
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Hi,

Quote:
Originally Posted by dimitri View Post
Oh, really his? I thought Sanken did this 30 years ago
Lovely. I knew I could not be the only ho could see the potential in this principle...

So, maybe I'll try it.

Edit, sanken still make it...

http://www.sanken-mic.com/en/product....cfm/3.1000700

Ciao T

Last edited by ThorstenL; 5th November 2011 at 03:23 AM.
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Old 5th November 2011, 05:06 AM   #17583
rsdio is offline rsdio  United States
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Quote:
Originally Posted by ThorstenL View Post
Really, so you mean using two DAC's in parallel reduces SNR by 3dB?
You started by claiming that two analog signals in parallel (balanced) reduces S/R by 3 dB. Now you doubt my claim that two DACs in parallel would suffer the same 3 dB S/R reduction? Is there some magic that spares us from the usual rules, or are you claiming that the DACs are noise free, or are you claiming that their noise is perfectly matched and therefore cancels out?

Quote:
Are you sure you really understand how the PCM1704 works?
I only know what the data sheet documents. They mention "dual balanced current segments" and "away from zero with small steps in both directions," both of which seem to describe a balanced pair of DACs. Also, the block diagram on page one clearly shows the current output from each DAC being combined before it is presented on a single output pin. What is wrong with my suggestion that each DAC be brought out to a separate pin where they can be combined or not by the circuit designer?

Are you sure you really understand how the PCM1704 works? It would be vastly more helpful if you tried to explain what you think you know, rather than tossing out nonproductive challenges.

Quote:
You don't? As it so happens I see one differential current output DAC for left channel and another for the right channel. Makes two DAC's in my milmaid 1 + 1 = 2 calculation, but WTFDIK.
I'm talking about "per channel" - of course a stereo DAC has 2 independent DACs internally, but they're each working on a separate channel. My apologies for not holding your hand through all of this discussion, but you first act like you don't need any help understanding this sort of thing and then you act confused by a simple omission that should be plainly obvious in the context of the conversation.

Are you trying to dither this thread by injecting "fuzzy" noise?
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Old 5th November 2011, 05:59 AM   #17584
ThorstenL is offline ThorstenL  Germany
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Hi,

Quote:
Originally Posted by rsdio View Post
You started by claiming that two analog signals in parallel (balanced) reduces S/R by 3 dB.
I did not claim anything. I merely observed the facts. If your electronic knowledge is so limited that you cannot handle basic noise calculations I am happy to demnsotrate for you how it is done.

Quote:
Originally Posted by rsdio View Post
Now you doubt my claim that two DACs in parallel would suffer the same 3 dB S/R reduction?
Of course I do, since it runs counter to the laws of physics as they are currently understood. If you have new ones maybe you publish in "Nature", rather than here?

Quote:
Originally Posted by rsdio View Post
Is there some magic that spares us from the usual rules
But this magic seems to apply where you are, so instead of suffering the unavoidable 3dB noise penalty (based on the "all else being equal)" dictum of course) thay have a 6dB noise advantage and paralleling two DAC's decreases
SNR by 3dB, instead of increasing it, as the laws of physics demand.

Quite frankly these are some of the most bizarre claims in a long time and so far off base, I'm gobsmacked...

Not that any of this particulary matters in the case of the PCM1704.

Quote:
Originally Posted by rsdio View Post
I only know what the data sheet documents.
This sufficies, but I do happen to know a bit more.

Quote:
Originally Posted by rsdio View Post
Are you sure you really understand how the PCM1704 works?
Yes.

Quote:
Originally Posted by rsdio View Post
It would be vastly more helpful if you tried to explain what you think you know, rather than tossing out nonproductive challenges.
First, you are the ones who knows everything better anyway, so you explain it, secondly, if you need EE remedials, my hourly rate is a reasonable 50 Euro.

Quote:
Originally Posted by rsdio View Post
I'm talking about "per channel" - of course a stereo DAC has 2 independent DACs internally,
As the PCM1704 is a single channel DAC and you did not elaborate your application (which could have been non-audio) you may have found the second channel redundant and hence the Arda Tech DAC not suited for your project on BOM cost. That was all.

Quote:
Originally Posted by rsdio View Post
Are you trying to dither this thread by injecting "fuzzy" noise?
Well, let's see? Who is making claims that have no basis in physics as they are currently understood and constantly uses counter factuals in his arguments here?

So I really think I am best off with taking Bob Adam's advise to Scott Wurcer for myself as well.

Qui ignorabat, ignorabitur

Ciao T

Last edited by ThorstenL; 5th November 2011 at 06:02 AM.
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Old 5th November 2011, 06:16 AM   #17585
Joachim Gerhard is online now Joachim Gerhard  Germany
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The Josephson is another one : http://www.josephson.com/pdf/srs7.pdf
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Old 5th November 2011, 06:49 AM   #17586
john curl is online now john curl  United States
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Thorsten, I agree with you about the 3dB, but you don't have to rub it in. This is just an 'oversight'. As I am not allowed to severely criticize anyone, I don't think that you should either. '-)
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Old 5th November 2011, 08:37 AM   #17587
ThorstenL is offline ThorstenL  Germany
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Hi John,

Quote:
Originally Posted by john curl View Post
Thorsten, I agree with you about the 3dB, but you don't have to rub it in. This is just an 'oversight'. As I am not allowed to severely criticize anyone, I don't think that you should either. '-)
With age comes wisdom.

I see you posses much of it and are very tolerant to others flaws, a virtue I am rather lacking, I must admit.

I, meanwhile, feel the getting older, but wisdom escapes me.

Plus, a severe failing of mine that I am keenly aware of but have yet to change, I have a low tolerance of those who criticise my knowledge and understanding of advanced electronic concepts (quite rudely at that) and then reveal themselves to be sorely lacking in very basic electronic knowledge (never mind more advanced concepts), plus I am rather allergic to Merda Taurorum.

I was actually very tempted to take recourse to more robust anglo-saxon vocabulary here, but I shall contain myself to avoid winning another all expenses paid holiday in Sin-Bin-City, where the grass ain't green and the girls ain't pretty.

So, being the wise and tolerant person you are John, I am sure you can forgive my foibles and youthful, if unwise exuberance.

Caelum, non animum, mutant, qui trans mare currunt.

Ciao T
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Old 5th November 2011, 09:11 AM   #17588
john curl is online now john curl  United States
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Thorsten, I just want to keep you contributing. You have a much more detailed knowledge of digital and its weaknesses. I want to learn more, not get the debate left one sided.
I have known about digital's 'weaknesses' just from listening tests, first starting in 1968.
I was ever hopeful that it would improve in the early 70's with delay lines that we used for large concerts, but it didn't. Then a Philips Research Lab demo in 1974, with 14 bits and a 50K sample rate was pretty good, and I hoped for the future. In 1977 or so, Ampex started to make delay lines for analog record preview. We had a terrific fight over 50K vs 100K clock rates, and they settled on 50K, although we could hear the difference. Then Stockham came out with his digital recorder, and we competed head to head with it for the final mixdown of the Tusk recording. Stockham won out over me, but I then predicted that from what I heard, that this recording would fail in the marketplace, because of the digital addition. (The analog masters were just fine, I heard them repeatedly, myself in the studio in 1979.)
Digital, for me, has always been problematic, sonically. Perhaps, I just seem to be extra sensitive to it, intrinsically. So, now that 30+ years have passed, I still have problems with digital, both live vs recorded (as we do every year at CES), standard CD's, digital radio, TV, etc. I do feel that a basic 'rethink' of digital may be in order, rather than relying on today's specs and 'rationalizations' so that hi end digital can become COMPLETELY transparent.
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Last edited by john curl; 5th November 2011 at 09:32 AM.
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Old 5th November 2011, 09:27 AM   #17589
PMA is offline PMA  Europe
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John Curl's Blowtorch preamplifier part II
Quote:
Originally Posted by jcx View Post
I don't see the relevance to our discussion - these are pipelined flash converters - not Delta-Sigma
I would like to see similar measurement for S-D A/D converter. I have never seen something similar, maybe I am just only not aware of it and there might be many who have already done it. Anyway, it is not as simple to make such measurement as to type on PC keyboard in a high-end pub.

I am with Thorsten here - not so much interested in long-run averaged FFT captured on periodic signals. Once again, rising transients are very, probably most important for human hearing and such signals should be investigated. Music is in fact a stream of transients, rather than 1 minute lasting 1 or 2 sinuses, that may be easily averaged.
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Old 5th November 2011, 09:31 AM   #17590
john curl is online now john curl  United States
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Right you are, PMA!
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