Hi Guys and Gals,
I'm finalising the design of my GC chassis using BrianGT's boards, and have realised that i probably won't get enough passive cooling and will have to add some fans.
I've read several comments with regards to interference from fans but i don't think i've noted anyone that has done a proper test.
Unfortunatly i'm not in a position to do such a test yet so......could some one do one for me
?
Something along the lines of a 40mm pc fan or similar about 50mm ( 2 ") from the chip with a 5mm piece of aluminium seperating them.
I'm going to some considerable trouble to route power, input and output wires away from each other. The last thing i want is to sit down for an evening with Mr Satriani and have Joe Papst buzzing away in the background .
Why is nothing ever easy ?
I'm finalising the design of my GC chassis using BrianGT's boards, and have realised that i probably won't get enough passive cooling and will have to add some fans.
I've read several comments with regards to interference from fans but i don't think i've noted anyone that has done a proper test.
Unfortunatly i'm not in a position to do such a test yet so......could some one do one for me
?Something along the lines of a 40mm pc fan or similar about 50mm ( 2 ") from the chip with a 5mm piece of aluminium seperating them.
I'm going to some considerable trouble to route power, input and output wires away from each other. The last thing i want is to sit down for an evening with Mr Satriani and have Joe Papst buzzing away in the background .
Why is nothing ever easy ?
The trick with fans is to use a large diameter fan, running slow. This cuts the acoustic noise dramatically. The other good trick is to use a variable speed fan, controlled by a thermistor on the heatsink. So at low volumes, when there's not much heat dissipation the fan runs slow, and at high volumes the fan speeds up - but you wont hear it because of the loud music 
.
As for electrical interference - use an AC fan if you don't want speed control, or a separate DC supply just for the fan for DC fans. Magnetic coupling can be over come by mounting the fan on the case, sucking air in, then venting out past the heatsink with some simple ducting. This keeps the fan away from the amplifier electronics.
I'm going to be fan cooling my 5 ch 100w/ch GC using 2x 80mm speed controlled DC fans, mounted on the case.
.As for electrical interference - use an AC fan if you don't want speed control, or a separate DC supply just for the fan for DC fans. Magnetic coupling can be over come by mounting the fan on the case, sucking air in, then venting out past the heatsink with some simple ducting. This keeps the fan away from the amplifier electronics.
I'm going to be fan cooling my 5 ch 100w/ch GC using 2x 80mm speed controlled DC fans, mounted on the case.
Maybe another option
Hiya,
Just thought I'd offer some alternatives. I've been looking into this myself, as I'm a complete noob to Audio, but do the Computer thing to a high level of anal-retentiveness.
Have you considered just using a large thermal mass? (i.e. big chunk of metal). Heat pipes could also be used to move the load to another area where you could get the surface area to dissapate it. Vents would also be beneficial here.
Or the real suggestion;
Ducting, so very simple, move the noisy component away from the sensitive components. Since fields dissapate at Log-2 attenuation, every bit of distance really helps.
I haven't done any emperical testing on fans (I would suggest SilenX or Papst for high quality, high performance fan solutions), but have plenty of experience with the crappy grade of fan and interference and noise at frequencies that just pierce through any other noise.
I'd suggest the 60mm or 80 mm fan, better performance spec's.
Hiya,
Just thought I'd offer some alternatives. I've been looking into this myself, as I'm a complete noob to Audio, but do the Computer thing to a high level of anal-retentiveness.
Have you considered just using a large thermal mass? (i.e. big chunk of metal). Heat pipes could also be used to move the load to another area where you could get the surface area to dissapate it. Vents would also be beneficial here.
Or the real suggestion;
Ducting, so very simple, move the noisy component away from the sensitive components. Since fields dissapate at Log-2 attenuation, every bit of distance really helps.
I haven't done any emperical testing on fans (I would suggest SilenX or Papst for high quality, high performance fan solutions), but have plenty of experience with the crappy grade of fan and interference and noise at frequencies that just pierce through any other noise.
I'd suggest the 60mm or 80 mm fan, better performance spec's.
Vikash said:
The actual GC board will be housed on a piece of aluminium bar that is 60mm in diameter with a large section (pocket) milled out for the board to sit in. Probably equivalent to a 25mm x 50mm rectangular bar in mass . An acrylic tube is then slid over the bar to enclose the board but leave it visible. Brian did a sterling job on designing them so i figured they should be seen not hidden away. There are four of these which house the 4 channels and are connected to 2 40mm copper tubes running front to back.
Kinda like this if you view it from above
An externally hosted image should be here but it was not working when we last tested it.
The fans are to be housed in the ends of the bars that house the boards and draw air over the boards.
In the big gap in the middle are 2 circular "cans" milled from ali and joined to form a figure 8 that house the troids.
So you see large fans are out.
I dont need a lot of air, just enough to do the job
Hope that all makes sense.
Do fans stall if you run them with to low a voltage ?
mateo88 said:
Matt makes a good point -- air will move itself at around 32 linear feet per minute (just think how slow you have to walt to cover 32 feet in one minute). A 12 V fan run at 7 volts will move a decent amount of air with few decibels of audible noise.
Getting the heat sink fins so that they are perpendicular to the ground helps (if you aren't going to be moving air.) If the fins are parallel to the ground they just heat each other up.
I found that with my bridged amp the heat sink would go over 200 degrees fahrenheit without the fan, with the fan it was around 105 -- this when it was putting out over 100 watts.
with all due respect to Douglas Self, the distortion was higher when the devices were at their "distress" point.
karma said:try it without. u can add one later if its to hot. witch likelly will not be the case
just leave the top open so it can vent . and u can see brians work
You don't seem to understand...
the diagram above shows pretty much the whole structure. It's just tubes with a couple of large canisters for the troids. There is no top or base or sides, everything is housed/routed inside the tubes. There is no vertical flow path for the air, it's all horizontal, so passive convection airflow will be next to none.
There is plenty of mass however so maybe i'm going overkill with the fans
I picked up the Ali and perspex tubes and the 140mm round Ali blanks for the troid housings today, just gotta get this oak table i'm building finished then i'll make a start.
I will inclued mounting points and cable routing for small 40mm fans but will decide if they're needed after testing.
I will however need to find a way of powering the LED's and fans (LED's and FANS !!!! on a GC!!! am i mad
) Does anyone know of a simple small psu that can provide 5v to 12 leds and 4 fans it has to be less that 35mm wide and 20mm high? I'm so pushed for space that i'll probably have to add an extra set of windings to one of the troids to give me the 5v AC that i need, any suggestions on how to go about that ?Is anyone interested in a diary type thread that details the building of the chassis ?
Ever heard of the term "form follows function"? Seems to me you are trying to make it work just because it looks "cool". I don't want to sound harsh, but maybe you should have thought the design process through a little more before purchasing the materials. Amplifiers produce heat, and you need to take that in to account when designing the components and layout.
chrish said:
Chris, thanks for your input. I do take your point, although i feel you are a little blinkered in your view of design. There is no reason that these things can't look good, even if it means that some difficult hurdles have to be overcome to achive the desired results.
I do admit that i'm a complete novice when it comes to designing amps, but i do know what i like and for me the learning process is the most important factor.
Now, can you help with my problems or do you fancy another bash at my design philosophy
I don't think anyone's bashing your design phil.Selexus said:There is no reason that these things can't look good, even if it means that some difficult hurdles have to be overcome to achive the desired results.
I do admit that i'm a complete novice when it comes to designing amps, but i do know what i like and for me the learning process is the most important factor.
Now, can you help with my problems or do you fancy another bash at my design philosophy
but many of us share the philosophy not to introduce unneccessary complications and complexity - kind of a gainclone theme in some ways Many designs can be tiny and aesthetically appealing without resorting to fans for cooling (which I find absurd personally). But who am I to question your taste, and if you feel a fan will better fit your requirements then modding your design to incorporate better heatsinking, then at the least we all like to see different/innovative designs 
I can't really tell what your intention is from the pic you attached. Can you draw it out differently, or maybe from some other views or something. We might be able to pitch ideas in better...
Vikash said:
I don't think anyone's bashing your design phil.
Fair enough.
I must say that yes i am driven by looks as much as sound quality. I see these projects as a learning exercise and engineering test as much as a means to great hi-fi.
OK.
If you take a look at this headphone amp i built
An externally hosted image should be here but it was not working when we last tested it.
and imagine the two long copper tubes rotated so that the feet are pointing horizontaly outwards. Where the feet are will be the PCB tubes, and where the curved centre section is will have 2 round housings for the troids.
I hope that makes things a bit clearer
Maybe if i add a little length to the pcb mounting bar i can machine deep grooves into the outer ends that create radial fins. it would look like 4-5 equally spaced large washers on the end of the tube, if that makes sense ? like the groove in the feet above but thinner and more of them.
Selexus said:
I will inclued mounting points and cable routing for small 40mm fans but will decide if they're needed after testing.
I will however need to find a way of powering the LED's and fans (LED's and FANS !!!! on a GC!!! am i mad
Is anyone interested in a diary type thread that details the building of the chassis ?
Been thinking of this since yesterday, have some other ideas for you to ponder.
I'd suggest you go overly nuts with the fit & finish of your amp. With all those tubes, you'd actually have a fair amount of surface area, and if the fit is better, then there will be stronger coupling between various metal components, letting them transfer heat to and from each other. Lapping and a good thermal compound would definitely help here (Arctic Silver Ceramique would be a good choice, Arctic Silver is the manufacturer, non-conductive performance thermal compound.www.directron.com has a 22g tube for $6.99 US)
Considering the effort that you're going to for the case, I would suggest against the 7v or 5v under-volting fan solutions, most of the DC fans that you'll find are for computers where the 12v rails are standard to the ATX form factor. A 'noisy' fan generally doesn't have as high build quality or is built purely to move alot of air, as opposed to something specifically designed for quiet, so you're trying to conteract the noise, rather than deal with it immediately.Silenx makes a very quiet 40mm fan, expensive though. 5v won't stall a fan 12v fan, but might not start it. Papst makes some small 5v fans, but they also make some AC fans, tap right off of your main's line, then you don't have to worry about rectification.
I couldn't find a small PSU at your given dimensions, even the smaller PSU's... well, I wouldn't trust them, some of them just look shoddy.
I would be interested in seeing some photos
Cheers
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