|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
50.159.77.150
In Reply to: RE: Linear Power Supply or Battery on Mac Mini - pics posted by AbeCollins on December 21, 2014 at 20:42:19
"But how do you know that these 'droops' are detrimental ?"The circuits that the power rail is feeding will have some inherent noise rejecting character. The key to success is understanding this character, what the supply can deliver, and how the resulting performance due to interaction of power supply and the load circuit systems compare with required performance. It's a multivariable equation at least.
"And remember, those measurements were taken before the additional filtering module installed within the Mac Mini. And another thing, decoupling caps right at the Vcc source pin to a component tend to help with those fast 'droops'. There are several such caps in most digital designs."
It's true, for differential noise measurements like this you definitely have to measure right at the load to get a realistic idea of what is truly going on where it counts. Measuring upstream of the filtering will tell you very little about the power quality as seen by the load.
Though most audio gear these days, depending on application of course, is pretty awesome at rejecting differential noise but much less effective at rejecting common mode noise which is coincidentally cropping up more regularly.
Less talked about and less well spec'd on power supply equipment is the common mode noise performance on the outputs with respect to earth referencing as most common audio equipment uses. Getting common mode noise way down in earth referenced audio gear power supplies is critical. The humongous problem here is testing gear for doing proper evaluation at an audiophile level is going to cost a fortune. Your 8 bit scopes and high end fluke dmm's just wont have what it takes to see -120dB throughout the audio band and a preferably a reasonable bit beyond. A good audio adc could probably be helpful fur the lower frequencies but what about the 200kHz and up? the answer is $$$$$ gear I can't afford. Even my work won't buy that kind of stuff. It's specialty gear and gonna cost ya.
Edits: 12/23/14Follow Ups:
I mostly agree with you. But as I mentioned to fmak (who can't seem to understand), my measurements are part of a preliminary functional test, i.e. does it appear within reason and does it work?
It's true, for differential noise measurements like this you definitely have to measure right at the load to get a realistic idea of what is truly going on where it counts. Measuring upstream of the filtering will tell you very little about the power quality as seen by the load.
Absolutely! With hundreds of individual 'load points' (Vcc pins) to test within the computer, and the thousands of variables which can affect the results, we can only assume that the power at each 'load point' is sufficient for proper operation.
On a larger scale, I don't own a high-end spectrum analyzer to view the end result at the output of the external DAC or power amp. There are very few here who do. At least one manufacturer has posted a screen shot from an Audio Precision analyzer.
"Absolutely! With hundreds of individual 'load points' (Vcc pins) to test within the computer, and the thousands of variables which can affect the results, we can only assume that the power at each 'load point' is sufficient for proper operation."
There are billions of load points in a computer, but most of them are inside the chips and hence inaccessible without very specialized equipment. The real issue is the definition "proper operation".
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
"The real issue is the definition "proper operation"."
Who else would define it besides the component manufacturer? If a manufacturer doesn't supply the info good designers need the good designers won't use their stuff.
"The real issue is the definition'proper operation'."Who else would define it besides the component manufacturer? If a manufacturer doesn't supply the info good designers need the good designers won't use their stuff.
Not correct. The proper operation of the chip according to the chip manufacturer does not necessarily imply proper operation of the motherboard according to the computer system manufacturer. The proper operation of the computer system according to the computer system manufacturer does not imply proper operation of the audio playback chain, according to the audiophile who assembled the playback chain.
If there were complete and accurate engineering specifications at each level and designs used subsystem components in accordance with these specifications, then these problems would not exist, or at the least, it would be possible to identify a particular organization or person who screwed up. However, this is not "real world". This is a particular problem when a digital computer system is used as part of an audio chain that has inadequate isolation from digital noise. Here, there are no specs whatsoever, e.g. there is no DAC on the marketplace that quotes isolation from power noise or digital interconnect noise. Indeed, there is no standard or even widely known method of measuring the impact of this noise on the audio output from the DAC. There are no known engineering methods of correlating measurements with sound quality.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Edits: 12/26/14
"Not correct. "
Sure it is. At each level of system complexity you get the choice of going integrated or piecing together discretes of your own choosing. Going integrated allows one the luxury of leaving the worrying up to the manufacturers. Limiting your choices to what has been integrated and made commercially available obviously has it's limitations as well. pick your poison.
But for practical reasons we can't get to the 'load points' within a chip so that's why I reduced the count down to hundreds. ;-)
Since we're talking about a computer, and I was talking about preliminary functional tests.... The fact that the computer boots up on the various power supplies and is working as a computer should and like it did before, that would be my definition for 'proper operation'.
You don't need an 'audiophile' power supply to make a computer operate properly.
there is no point in any tests, preliminary or otherwise, if you don't carry out the preliminary setup correctly. This is the first mandatory step towards any credible test or meaurement.
You appear to be repeating yourself at every opportunity that my setup was not correct for the preliminary functional tests that I was performing. So please explain what was not correct for these specific tests.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: