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RE: PSU linear power -again!

The no-longer-active and lamented JackWong96 seemed to have the best grasp of how power is used on motherboards. He describes some of that in this post:

http://www.audioasylum.com/cgi/t.mpl?f=pcaudio&m=75904

But noone has yet performed and published a comprehensive survey of all of the voltage consumers on the recommended motherboard(s) AFAIK, sorry.

I do suspect that 3.3v is only being used to power some of the less-critical circuits in the MoBo, but I am not sure if you'll get a good boot without that voltage. Worth a try... Mihaylov, Bibo01, or others, have you tried booting one of these boards with the 3.3v not active? JackWong96's experiments with removing and/or un-powering various peripheral chips did strongly suggest that the board will not be upset if at least some of the non-core chips were not active, so you might get away with this. I do know that with the GA-G31M-S2L mobo, I am only supplying about .3ma on the 3.3v line, so it is lightly used at best. JackWong96's experiments suggested that a number of the uses were non-critical chips (like the DVI to HDMI converters) and removing them and similar chips nearly halved the power consumption on that line.

Then on grounds, as Mihaylov has indicated, all of the grounds connect together at the ATX-24 socket on the motherboard (at least on the Gigabyte boards we are using... I haven't looked at every board out there!). That is also true for each of the multiples of the same voltage rail... for example, all the 5v connections on the ATX-20/24 come together at the socket on the mobo.

One technique I've seen recommended is to pair each voltage line with a corresponding ground line to minimize the radiated noise and magnetic fields. On my supply, I used twisted pairs or braided triples or quads for this. I used a 20-pin plug (see attached picture for a good diagram)



I paired up the following:

- For +5v, I paired up the grounds on pins 16 & 17 with the +5v on pins 19 & 20 into a 4-cross braid. I also paired up the grounds on pins 5 & 15 with the +5v on pins 4 & 6 for a 2nd 4-cross braid.

- For +12v, I paired up the ground on pin 7 with the +12v line on pin 10 as a twisted pair.

- For +3.3v, I combined the +3.3v lines 1, 2, & 11 into one wire, then twisted that with the ground on pin 13.

- For the +5v PWR_OK & +5VSB on pins 8 & 9 respectively, I used the ground on pin 3 with them to make a 3-wire braid.






Of course, feel free to make your own choices for pairing wires up if you decide to do this.

Bibo01, thanks very much for the Molex part numbers. I used a scavenged ATX-20 connector for my 1st supply, but I'd like to do it with a virgin connector for my next. You've made that easier!

BTW, to confirm something I said in my monster Juli@ mod thread awhile back, that soundcard does not use the 3.3v from the motherboard. This doesn't appear to be useful for anyone involved in this sub-thread now, but might be useful to someone else making their own linear supply another time.

Best of luck to you on this. I think you'll find it very rewarding!

Greg in Mississippi

P.S. I've been corresponding separately with another inmate who has posted here very little. He worked up a linear supply for his cMP and it had easily adjustable voltages on the 5v and 12v lines. He played with them and found that lowering them by something in the range of .2v -.4v produced SQ benefits. I know he's been otherwise-occupied and I'll let him tell his story when he can, but based on his experiments and similar accounts others posted here in the past, I tried it and found it worthwhle too.
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