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Old 28th August 2013, 05:01 PM   #11
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What type of capacitor is suitable for this sort of project?

Not too sure, really. As there is bound to be plenty of decoupling capacitance and very likely switchers too on the MB, not sure it matters a whole lot. Now if motherboards came with a circuit...
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Old 28th August 2013, 05:07 PM   #12
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An what about the noise generated inside the mother by the digital signals? Noise by the SMPS is ultra-audible, noise in the mother system may not. Also SMPS noise i relatively fixed in frequency, mother noises doesn't ‼
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Old 28th August 2013, 06:03 PM   #13
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Ehm, what about?

One bit at a time. If we cannot design the MB, let's at least do what we can.

Crom's post indicates that he has removed one of the MB switchers. Whether it's possible to take them all out i have no idea, it probably is very MB specific.

Otoh, MBs are designed with care for PS and RFI emissions, are they not? Groundplanes, multilayers, software optimisation and simulation at RF. Maybe on-board generated interference is less harmful than quickly hacked together high power switchers like the nano or pico...

Not sure how true this is, but i distinctly remember a manufacturer of high end music servers touting custom designed, switcher-less MBs...
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Old 28th August 2013, 06:15 PM   #14
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There are various guys on here that I've talked to (eg Mace...sorry, might be Marce) on here who are clearly v knowledgeable about smps and I am sure it's possible to build an excellent quality smps (it must be...the hypex amps sound great). I've done some research but I'm in the following rather than pioneering camp at the moment and until I have something I can follow and then experiment with I'm going to stick to linear.

I don't entirely agree with Osvaldo that the MB smps noise is audible but the sound I've got out of my motherboard has certainly improved when I've got rid of smps where possible.

analog_sa: I can't post pics but take a look in the computer audio section of audio asylum and I think i posted some direct links in the computer audio section of the jplay.eu site. There's plenty of reading to do in both of those. AA is especially DIY friendly and that's where I got the RAM tip from.

Basically, the idea is that you remove the coil that is part of the RAM SMPS (there maybe one or two depending on how many slots you have). Then you can directly feed the RAM. Turn the MB on and put a multimeter between ground and the two holes where the coil used to be and you will see which one has a voltage on it. the hole that doesn't should be the one that gets your outside 1.5v. Only slight complication is that your external feed needs to be connected to the ground rail of the MB. Currently I just switch on my feed to the RAM and CPU before I trigger the MB to power up. It's a little hassle but works for the moment.
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Old 28th August 2013, 06:23 PM   #15
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Yes, the mother noises are audible. I have (At this machine) I can hear HDD access and other video-related noises in the speakers.

At home, in a 486 with old SB16 and win 95, noises are far worse than the same machine under pure DOS 7.10, the system being the same.
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Old 28th August 2013, 07:31 PM   #16
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Yes, the mother noises are audible. I have (At this machine) I can hear HDD access and other video-related noises in the speakers.

At home, in a 486 with old SB16 and win 95, noises are far worse than the same machine under pure DOS 7.10, the system being the same.
From your description it is only cleat that a bus-powered soundcard is sensitive to power supply noises on the motherboard. It is not at all clear if switcher noises play any role in this at all. I am not even sure 486 boards had any switching regulators on board - they may have well been all linear
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Old 28th August 2013, 07:32 PM   #17
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Crom,

Thanks for this - it is very clear. Somehow i must have missed the relevant discussion at the Asylum.
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Old 28th August 2013, 07:46 PM   #18
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Originally they had a bipolar plus TL431, I tuned to IRF540 + TL431.
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Old 29th August 2013, 12:31 PM   #19
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Originally Posted by Crom View Post
There are various guys on here that I've talked to (eg Mace...sorry, might be Marce) on here who are clearly v knowledgeable about smps and I am sure it's possible to build an excellent quality smps (it must be...the hypex amps sound great). I've done some research but I'm in the following rather than pioneering camp at the moment and until I have something I can follow and then experiment with I'm going to stick to linear.

.
I think the Class D amps such as Hypex are a special case because the required filter deals with the SMPS noise.

I suspect there are two broad camps here: (1) those dependent (like me for now) on S/PDIF from the audio server (I use an ESI Juli@ XTe card) and (2) those using asynchronous USB setups into either asynchronous DACs or USB->SPDIF converters. Those in camp 1 care a lot about the power supply in the audio server. For those in camp 2, the challenge is achieving galvanic isolation from the audio server (as the data is packeted and the source clock not relied on). If you do this well, you don't need to care about the audio server PSU.

From what I can gather, the best current implementation of (2) is the use of a Berkeley Alpha USB S/PDIF converter. I would venture that most, however, are simply deploying USB cards such as the SoTM card straight into an asynchronous DAC (of varying quality).
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Old 29th August 2013, 01:36 PM   #20
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From what I can gather, the best current implementation of (2) is the use of a Berkeley Alpha USB S/PDIF converter.
Why on earth would this be a good idea? Let alone "best"? And what difference does the quality of clocks they use make, if there is a subsequent decoding of spdif back to i2s with either new, or God forbid, recovered clocks?

Last edited by analog_sa; 29th August 2013 at 01:39 PM.
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