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 Post subject: Replacement ATX PSU for old Mac - recommendations?
PostPosted: Sun Oct 23, 2011 12:13 pm 

Joined: Sat Mar 31, 2007 1:15 pm
Posts: 15
Hi people

Well the PC I built in 2007 with advice from people here is still running like a dream, now primarily on Ubuntu Lucid Lynx - four years of lovely quietness and counting, touch wood :-)

Meanwhile I've also quietened down my old G3 "beige" Mac, by suspending some 2.5" drives in elastic and replacing the case fan & PSU fan with quieter ones. That's not as quiet as the PC though. And the latest is, its power supply seems to have died.

So it's the Mac I'm writing about today. This is actually a G3-desktop motherboard with a G4 processor in a "beige" G3 tower case, bit of a hybrid.

What occurs to me is that if I'm buying a new PSU anyway, I may as well take the opportunity of seeing if I can make the machine a bit quieter.

The tower version uses a standard ATX PSU, so I've got a lot of choice about what to put in instead. This one's labelled for 171W. It's nothing special, just the one which came with the case, except for the Nexus fan I swopped in. The PSU's got a cut-out grille rather than a wire grille so that's one possible improvement for the next.

I started by reading the SPCR "recommended PSUs" page, plus an older one of those via the Internet Wayback Machine. But this is actually not as useful as it might be, because I'm not starting with a blank slate - I've already got the case which it's got to fit. And I'm a bit iffy about whether any of the "Editor's Choice" or "Recommended" PSUs is really sensible for this machine.

Label of the probably-dead power supply tells me:
+5.0V - 21.0A }
+3.3V - 14.0A } Total of those two 121W max
+12.0V - 6.1A
-5.0V - 0.3A }
-12.0V - 0.8A } Total of those two 0.8A
+5.0VS - 0.1A
Total: 171W max

Outputs: It's got a 20-pin plug for the motherboard, and everything else seems to be coming via Molex plugs, with various adaptors - to a CD writer, two hard drives and the case fan. I seem to remember tinkering with one of the Molex adaptors to undervolt the case fan when I did the previous round of quietening, can't remember the details of that now - I think it was probably a potentially-12V fan which I'm running at 5V.

Power use: I don't know what the machine's actually drawing. I mostly use it for running an old version of ProTools, not generally with more than a few tracks simultaneously. I don't think that works the machine very hard, and I haven't had any noticeable problems with overheating, with the possible exception that a couple of times on unusually-hot days the fans seemed more noisy than usual and I've switched it off to be on the safe side. (but that might have just been me being over-cautious :-) )

So, getting back to current options:

The "12cm fan at the side" PSU form (as in some of the recommended Seasonics) looks a bit dubious to me for this machine, because that side of the PSU is basically adjacent to that side of the Mac's case. It's so close, it's hard to tell what the gap is, but it can't be more than 1cm and could be less. I suppose I could cut a hole in the side of the case, but that would be a bit drastic, and might be a silly idea anyway in terms of keeping the noise down.

So I'm curious about those - are those designs meant to work like that or are they intended for a location with more space next to the fan? and, supposing they did cool properly in this location, would the proximity of the fan to the side make them noisier than they would otherwise be, and/or noisier than the best "ordinary" 8cm-fan designs?

I'd certainly consider fanless, but that might be (a) overkill by way of expense (and power?), and/or (b) insufficiently surrounded by cool air - again, considering the amount of the PSU-space that's closely surrounded by case etc in this case design. Comments on that welcome.

I'm open to argument as to why either of the above would in fact work fine despite my caution! But what I'm thinking I probably want/need is a recommendation for something that
- is efficient in whatever range of power the machine's likely drawing (estimates of that welcome, but presumably <171W),
- is quiet, or at least quieter than the previous one
- has an 8cm fan in the position where the Mac case "assumes" the fan will be
- pops up on second-hand every now and again :-)

I don't mind replacing the PSU fan, did it once can do it again (& can even re-use the same one unless that's died), but obviously it'd be nice if it came with a quiet enough one that I didn't have to bother.

Thanks in advance for any thoughts!

 Post subject: Re: Replacement ATX PSU for old Mac - recommendations?
PostPosted: Sun Oct 23, 2011 2:34 pm 

Joined: Wed Jun 13, 2007 10:12 am
Posts: 5275
Location: ITALY
...snipped out (maybe it's too late to type correctly)...


Support SPCR, use these links when you buy: NCIX, Amazon and Newegg

 Post subject: Re: Replacement ATX PSU for old Mac - recommendations?
PostPosted: Sun Oct 23, 2011 3:29 pm 

Joined: Thu Oct 06, 2005 4:36 am
Posts: 7016
Location: Monterey Bay, CA
A little more on the above comment: ATX revisions since the G3 beige came out include moving most of the amperage away from the 5V and 3.3V lines to the 12V line(s)...

An example:
Kingwin Stryker 500W
3.3V, 20A
5V, 20A
12V, 41.5A

Pretty close to what you need - all of the recommended PSU's do list their supply you can pick one from there. Hard to say how much your configuration needs.

1080p Gaming build: i5-4670K, Mugen 4, MSI Z87-G45, MSI GTX 760 2GB Gaming, 8GB 1866 RAM, Samsung 860 Evo 500GB, Crucial MX100 256GB, WD Red 2TB, Samsung DVD burner, Fractal Define R4, Antec True Quiet 140 (2 front + rear) case fans, Seasonic X-560. 35-40W idle, 45-55W video streaming, 170-200W WoW, 200-230W Rift, 318W stress test (Prime95 + Furmark)

Support SPCR through these links: Amazon and Newegg

 Post subject: Re: Replacement ATX PSU for old Mac - recommendations?
PostPosted: Wed Oct 26, 2011 7:36 am 

Joined: Sat Mar 31, 2007 1:15 pm
Posts: 15
::reads things::

Thanks. That Kingwin does look very interesting.

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