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RE: another request for you to consider...

Posted by Ryelands (A) on January 13, 2009 at 06:36:07

In Reply to: another request for you to consider... posted by sondale on January 13, 2009 at 04:37:51:

sondale wrote:

> > ”I am just getting to modifying the psu on my pc (Gigabyte GA-G31M-S2L for cMP2) and so far I have followed Dave's suggestion of adding capacitance to the P4 connectors - this made a huge difference. What I would like to do is have a separate psu purely for this supply - it would seem that 12v @ 2A (max) would be sufficient.”

I’d better own up as sondale's idea of using a linear supply for the P4 12 volt line might have followed from off-list exchanges with me. I noted that:

“I repeated [on Sunday night] the measurements I did of the current drawn by the E7200 chip [on the G31 motherboard]. On power up. it draws about 1.5 amps. As ‘underclocked’ BIOS settings kick in during POST, this falls to about 0.6 amps. Once the OS is loaded and while playing music (with a NOS DAC), the chip draws between 0.4 and 0.5 amps or between five and six watts.

”Curious is the fact that the PSU I'm using allows one to trim the voltage. I can run the chip perfectly on 11 volts instead of 12. However, despite the reduced voltage, current draw seems to go up, not down. I do not know what is going on.

“What the measurements do suggest is that the 2-amp capacity of JS's design is meaty enough for the likes of the E7200 but could well be too small for older or more powerful chips. Moral: measure first! ”

I’m grateful to sondale for confirming that adding smoothing on the P4 12 volt line improved the sound of his system.

However, I would like to stress that using a linear PSU on the same line is a significant step up from that. It is not a "nuance" but arguably the biggest hardware-derived change to sound quality that I’ve made in the 15 or so months I’ve been building dedicated audio computers.

The device I used was a 5-amp US-made unit built like a tank and using the venerable ua723 regulator, a chip design now pushing 40 years old but still doing well. The next step is to try JS’s design set for 12 volts.

I would encourage users of cMP2 or similar high-resolution systems running on suitable kit to consider giving it a try though with the following caveats:

1. I have tested a separate PSU on the E7200 and on an eight-year-old Athlon XP chip only though I dimly remember other list members reporting doing the same on other chips;

2. the PSU should really be powerful enough to run the chip even if default speed settings are restored;

3. There is a chance, even with modern devices, that running with no load on the P4 12 volt line could make some PSUs unstable - it shouldn’t but it might. It needs testing;

Can anyone explain to this baffled tinkerer why the current drawn by the chip stays the same even or even rises if the supply voltage is dropped?

Best

Dave

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