Bypassing PCI card's bus power to External Power.
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Edwood

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OK, I want to bypass the PCI bus power from the motherboard to an RME digi96/8 PAD sound card.

Accomplished with cutting appropriate traces and soldering wires to an external linear regulated power supply.

More info here:
http://www5.head-fi.org/forums/showt...584#post778584

The problem is that voltages required are +3.3V, +5V, +12V, & -12V.

Also, the specs of the PCI pinout is very complex. It seems that the ground could be shared by input/output of data, and some of the data, as are possibly some of the voltages.

Anyone know more about PCI bus power?

-Ed
 
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Edwood

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I still want to do this. I won't know if it's beneficial until I've tried. I have a spare PCI riser adapter, so I can play around with this mod. I have a sacrificial POS sound card to try this one as well.

I want to mod the pci riser, so that this mod will be good for all cards that would be used.

-Ed
 
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jefemeister

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You will not achieve isolation by merely cutting into the power rails. the data lines are still made in reference to the mother board's power supply. You would have to acheive total isolation by using something like TI's ISO150 chip. You also have to make sure both supplies stay at the same ground.
 
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Stephonovich

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Actually, -12v is used solely by RS-232 (serial) ports, IIRC. If so, that cuts one requirement out of your problem.

As for the rest, sorry, I've never tried anything like this. I'd recommend e-mailing Dan of Dan's Data, myself. He likes weird stuff like this, and knows entirely too much about computers and power in general. No guarantee that you'll get a reply, but he does mention that if you happen to drop a few bucks in his PayPal account, he's much more apt to research it...
(very big site, actually. Lots of companies send stuff to him for review. Hence, lots of e-mails for help)

(-:Stephonovich:)
 
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Edwood

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Quote:

Originally Posted by jefemeister
You will not achieve isolation by merely cutting into the power rails. the data lines are still made in reference to the mother board's power supply. You would have to acheive total isolation by using something like TI's ISO150 chip. You also have to make sure both supplies stay at the same ground.


That's what I was afraid of.

So the data lines carry current to power the card?


-Ed
 
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jefemeister

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Quote:

Originally Posted by Edwood
That's what I was afraid of.

So the data lines carry current to power the card?


-Ed



say you have a clock that crosses the PCI slot. Which power supply is it "representative of"? It is shared amongst both. Therefore the noise on one side can cross right over to the other. An isolator has one supply feeding each side of the chip. The signal crosses through the chip by non-electrical means.
 
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Glassman

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yeah it's not ultimate isolation, but as long as we provide clean voltages to the card and reference our ground to the PCI bus ground it's ok.. you won't have clean ground, but at least clean supplies.. isolating whole bus is enormous effort not worth it..
 
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Edwood

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So it at least will be some measure of improvement. Only one way to find out. Can anyone make heads or tails of that link above showing the PCI's "pin" out?

Which ones (+12VDC, +5VDC, -5VDC) are power only?
Which grounds are power only? Would it be bad to bypass data grounds?

-Ed
 
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Stephonovich

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I'm assuming you mean this page, in which case, there's a pinout description at the very bottom. Unless I'm mistaken (quite possible), it shows quite clearly which pins provide power. However, this page (same domain) has a much better pinout, right near the top.

(-:Stephonovich:)
 
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Edwood

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The +5V or +3.3V (I/O) can also be bypassed? Is data carried on that line, or is it just saying it's power for the I/O?

Also, how many watts for each voltage?

I will try to measure if I can. I will definitely have to get smaller probes for my DMM.

-Ed
 
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Stephonovich

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my god, it's just a power supply, how would you carry data on power supply lines? all you need is common ground reference, then you can use your own power supply instead of those on PCI bus..
 
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Edwood

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Quote:

Originally Posted by Glassman
my god, it's just a power supply, how would you carry data on power supply lines? all you need is common ground reference, then you can use your own power supply instead of those on PCI bus..


Just trying to be a little careful at least.
I appreciate the help guys.

What do you mean by common ground reference?
Should I splice into the Grounds, or bypass all of them? Nothing looks fishy to me there. Looks pretty straightfoward to me.

-Ed
 
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