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RE: Linear Power Supplies for ATX & P4

Jack,

Not 100% sure what the issue was and not 100% sure I've solved it, but it's running longer now than it has before.

I suspect the fixed-voltage LT1083's were having momentary cutouts. Not sure why... they were well within their temp and current ranges. If it keeps working ok, I won't spend the time to try and determine the ultimate reason... just not worth spending the time when I have a lot of other things I need to / want to do.

I went back and looked at the datasheets for both the fixed and variable 1083's and realized I'd made a units mistake... they list max temps in the 150-200C range, I was reading temps of 130F! Big difference here... none of the chips should have had issues with this. It's hot... hotter than I like, but not over-temp hot.

In any case, I changed out the 5v ATX and 12v P4 regs from the fixed to the variable last night... it went longer before it cut out, so I thought I might have a bad chip in at the 12v ATX position, which was my last fixed one. So I replaced it with the 12v LT1083 that had been in as the 12v P4 chip and again it went longer... long enough that I thought it was fixed, but after putting the cover back on, it cut out again. So I took off the cover, did what I was trying to avoid and drilled ventilation holes above the heatsink, and tried it again. When that didn't fix it, I replaced that chip with another LT1083CP and for the last couple of hours, it's been good.

Preliminary sonic diffs with the fully linear supply... Significant improvement over the linear-hybrid supply (modified PicoPSU)... not as large as the difference between a modified Antec with additional filtering and the linear-hybrid, but VERY nice and worthwhile. Greater silence between sounds, more definition across the board, instrument and vocal textures are more audible, greater coherence between fundimentals and overtones. Stage width is surprisingly wider, didn't expect that. Curious how breakin will affect it... with some Black Gates & Jensen caps, it will be at least a couple of weeks before it finally settles in.

One interesting thing to note is that the motherboard is now stable with an even slightly lower voltage... I'm down to .72500 now with no sign of glitchiness at 192 oversampling, was at .73750 before with some glitchiness. This might be slight differences in voltage levels... need to measure exactly what my PicoPSU was putting out and what this one does. But I suspect it is having lower noise on the supply. Also, my Q&D check of listening for the level of interference on a battery-powered FM radio held near the computer shows it being much quieter than before.

Drawbacks are the time it took to debug it and get it working right... and the more-involved startup process. But I generally leave my cMP on full-time except when working on it or when thunderstorms are predicted, so that won't be a big issue.

While not quite as hard-core as your fully battery-powered setup, it is still pretty trick, with fully separate highly-over-spec'd supplies for each voltage. I want to play around with with different regulators along with powering the P4 from my dirty AC line (easy to do, just use my old supply for the P4).

I've been thinking about how to do a how-to guide... will post more about that in the next few days. Many thoughts here... there's not an easy way to do this and make it totally universal.

And I'll post more pix soon... my wife has the camera while she's off visiting her mom (in Hawaii!) and my cell-phone camera pix are just not that good.

Again, thanks for all your help.

Greg in Mississippi


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