Building F5 monoblocks in Apple G5 cases - diyAudio
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Old 14th January 2016, 11:05 PM   #1
njepitt is offline njepitt  United Kingdom
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Default Building F5 monoblocks in Apple G5 cases

Hi Everyone,

After a couple of years with no diy audio activity, I'm starting up a new project. Two or three years ago, while still living in Brazil, I started collecting parts to rebuild my F5; I liked the one I had built (original design, not turbo), but I thought I could do better with more care. Now I'm a bit more organised after moving in Maine I've decided to get moving and get it done. I have a pair of Peter Daniel's PCBs, a pair of 250VA toroidals, and various parts I can reuse from the old build, so the plan was (and is) a pair of monoblocks. Although I liked the heatsinks on the old build they were just a little too small, so I've bought four E008 sinks from HeatsinkUSA - which should be more than sufficient if I use two for each monoblock.

There is loads of information on this site on how to build an F5. The reason for a new thread is an idea I had for the chassis that I thought might be of interest to other people planning a Pass amp build, or anything similar. Rather than building a pair of chassis from scratch, I got a hold of some old Apple G5 computers that the university was sending for recycling. These are pretty heavy and very well made; entirely anodized aluminium, 1/8 inch mostly, with a little steel, and are extensively ventilated. On closer examination they have several other properties that are handy for repurposing them for amps; the power supply is in the bottom of the chassis (unlike the newer Pro models, where it is at the top) and is separated from the rest of the case with a steel sheet, so the trafo can be put there, and is screened form the rest of the circuitry. There is another steel shelf near the top, so any other circuitry like speaker protection circuits (or anything else, really) could be put up there if you want. There are also convenient (and well-designed) fan slots if you need/want them, although I don't intend to use them. Last, there is an excellent lever-action system for taking the side-panel off, which is very convenient for tweaking things later.

I'm attaching some photos of the how it looks with everything removed. Also a slight conundrum: the heatsinks are just a little too wide to fit side-by-side on the side of the cabinet, and I am reluctant to cut them, since I might want to use the cabinets one day for a larger amp build (F5 turbo or something else, who knows?). Anyone have thoughts on putting them as shown, one higher than the other but overlapping? Seems to me it would work well; it would mean mounting the pcbs with one mosfet vertically above the other, one on each sink, rather than placed horizontally, but that doesn't seem such a big deal.

I'd be interested to hear any comments, or any success/failure stories from people who have tried similar things. I'll post updates as things progress.

Nigel
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Old 14th January 2016, 11:29 PM   #2
njepitt is offline njepitt  United Kingdom
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The power socket on the power supply of the G5 has a heat-shrinked filter arrangement on it. I cut one open (since I thought the wires were a little too thin) so here's what's inside. The Y2 capacitor across the mains is 1uF, which seems high, although there are two other components which look like caps from live and neutral to earth, so maybe that affects things in some way. The ferrite is handy, and I expect to use it, with a 0.0033uF cap as in the original design and slightly heavier wires. Does anyone know for sure what the blue components are? The only marks I can read say CS102M so maybe they're Y class caps of some kind? Any point in keeping them?

Of course, a G5 computer pulls plenty of current, and this arrangement must be safe enough, so anyone who wants to can presumably use it without pulling the heatshrink off...
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Old 15th January 2016, 12:02 AM   #3
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I saw the heading and said "This I gotta see".

Congratulations, enjoy the result.

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Old 15th January 2016, 12:15 AM   #4
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Seems like a good idea to me.
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"If you leave this point unattached to some circuitry, an ideal constant current source will emit a small lightning bolt which will travel until it connects to something." Nelson Pass
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Old 15th January 2016, 12:20 AM   #5
njepitt is offline njepitt  United Kingdom
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Quote:
Originally Posted by Nelson Pass View Post
I saw the heading and said "This I gotta see".

Congratulations, enjoy the result.


Thanks, Nelson. Of course, I have to actually *finish* them first...
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Old 15th January 2016, 12:39 AM   #6
oohms is offline oohms  Australia
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how about using the heatsinks internally, and using low speed fans to pass the air from front to back?
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Old 15th January 2016, 12:58 AM   #7
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This project is asking for fan assisted heatsinks inside the case and some sound proofing on the chassis!!

With a tunnel heatsinks and 120mm computer fans you should be able to reach really good dissipation with really low noise, below 10db.
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Old 15th January 2016, 01:06 AM   #8
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2 of this sinks pr ch is overkill in a standar F5 (it looks as it is 10.080" profiles and about 8" long) you can do it with only 1 sink pr ch. I use 2 of this sinks (6" long) pr ch on my F5 with standar PSU voltage and 2.6A bias and 2 output pairs. and it stays at about 55C with 25C ambient temp.
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Old 15th January 2016, 01:18 AM   #9
njepitt is offline njepitt  United Kingdom
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Quote:
Originally Posted by oohms View Post
how about using the heatsinks internally, and using low speed fans to pass the air from front to back?
This is definitely a possibility which I considered. The design of these computers is very clever, and it looks like the plastic fittings that hold the fans can easily be replaced (more or less) after building an amp in the empty chassis, and putting fans in later would be simple if they are needed. I've heard that the original fans are noisy, although I haven't tried them, so you may want to change them for quieter ones of the same size. If you're going to use fans together with internal heatsinks, then another interesting possibility might be to find a way to use the (impressive!) heatpipe heatsinks that are on the processors in the G5. I thought about this, and may try it in the future; however I've also got a pair of (slightly) newer Apple computers with a different internal layout and different heatsinks that look like they might be a better choice than the G5 for this purpose.

For this build I'm going to stick with external heatsinks, mostly so that I have more space inside to experiment later; for instance, if I want to change to a CLC filter on the power supply then I'll probably need plenty of space.

Nigel
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Old 15th January 2016, 01:18 AM   #10
Bare is offline Bare  Canada
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As above, surprised to see passive sinks glued to the case exterior.
Necessary? there are 3 100 mm? fans inbuilt and one could easily upgrade those in both CFM and Silence. Lotsa market/product available for PC cooling. Air or Water
One can also buy 'cheaply' (80$) Antec Cases (comes to mind example only) that are designed for 6 100 /140 mm fans. All of which are sub 20db gizmos.
Only real issue is that a PC case can be a largish rascal

Last edited by Bare; 15th January 2016 at 01:22 AM.
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