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Old 4th April 2009, 11:49 PM   #681
Coulomb is offline Coulomb  England
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Default Re: but

Quote:
Originally posted by lgreen
But there are only 2 devices per heat sink, how hot can those little guys get??

Boy are you in for a shock!

Each one of those little guys is going to dissipate 32 watts, that means you are going to try to dissipate 64 watts off of one tiny heatsink that might be capable of say 20 watts or so. The devices will just destroy themselves in that configuration.

I am sorry but you need to rethink your case design, I know that sucks and please do not just take my word for it. I have been working on a GB for an adequate chassis for the F5 for quite a few months though, so I have some experience in this matter.

Regards

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Old 5th April 2009, 12:27 AM   #682
slam is offline slam  United States
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I use tea-baq's heatsinks which are bigger than yours. They run 26-30c above room temputure standalone (no chassis) -- Papa recommends 20c above. I would expect yours to run quite a bit hotter with your current placement.

You might want to monitor the tempeture very closely if you decide to go ahead.

While my amp is stable at 30c above. I was actually wondering if there is a possibility of thermal runaway...
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Old 5th April 2009, 12:35 AM   #683
labjr is offline labjr  United States
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Default Re: but

Quote:
Originally posted by lgreen
But there are only 2 devices per heat sink, how hot can those little guys get??
Try it and see? I think you need more heat sink. Also, it appears you have about .25 inch base. Maybe a little on the thin side.
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Old 5th April 2009, 12:51 AM   #684
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Just use a fan between those two heatsinks and things will be fine, you can adjust the speed so the noise shouldn't be a problem.
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Old 5th April 2009, 02:38 AM   #685
lgreen is offline lgreen  United States
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Default surprised

Well, my sinks certainly are not small, 8+ inches by 5+ inches? And solid!

But you all may be right, I'll watch the temp closely and report back. I was concerned one hot sink would be next to another hot sink, but no one said that the distance was bad.... just the puny size of those sinks! I'm telling you they are huge! They work!
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Old 5th April 2009, 03:52 AM   #686
Coulomb is offline Coulomb  England
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Quote:
Originally posted by Peter Daniel
Just use a fan between those two heatsinks and things will be fine, you can adjust the speed so the noise shouldn't be a problem.
Well yes a fan will dramatically improve the situation, I think one fan between the two might not work as well as seperating them and giving them each a fan. The risk of one fan is you will draw warm air off one heatsink and blow it across the other. The heatsinks will always be at different temperatures.

Quote:
Well, my sinks certainly are not small, 8+ inches by 5+ inches? And solid!
No they certainly are not small in stature, my comment was IMHO they are small for the task at hand.

Perhaps the best thing you can do is build it up, test run it and monitor the case temperature of your devices. If they start rising over 60Deg C. be cautious, when they get to 100Deg C be concerned, when they get to 120Deg C or higher then you have a problem as the junction temperature is going to be higher than that and has an operational limit on these devices of 150Deg C.

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Old 5th April 2009, 09:43 AM   #687
cviller is offline cviller  Denmark
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Quote:
Originally posted by sandbasser
I just entered an order on your website and paid via PayPal. There's no big rush on shipping as I'm currently recuperating from surgery and probably won't be able to use the boards for 3-4 weeks.

Thanks,
Thanks for your order - I expect to get the new boards very soon.
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Old 7th April 2009, 05:22 PM   #688
lgreen is offline lgreen  United States
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Quote:
Originally posted by cviller
21.6k should be just fine.

I have taken a few pictures and placed them here:
http://viller.eu/audio/2009jan_gbf5/pictures/

I might have some more detailed on another computer, but these were taken from a working one I finished last night. Hard to take pictures with all the wires...
Thanks, those are useful. I like the third pic.

I see that you have fastened Q1 to Q2, is that something that everyone should do, so they track each other's temperature?

Here is a pic of my first F5 board
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Old 7th April 2009, 05:57 PM   #689
cviller is offline cviller  Denmark
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Quote:
Originally posted by lgreen


I see that you have fastened Q1 to Q2, is that something that everyone should do, so they track each other's temperature?

You are correct that I'm trying to let them track better, but I doubt it makes a huge difference.
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Old 9th April 2009, 08:35 PM   #690
lgreen is offline lgreen  United States
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Default R5-R8

cviller- what does this mean (from page 5 of your assembly guide):

Quote:
Picture 4: Board before soldering in mosfets (the
R5,R6,R7,R8 solution is not recommended)
What do you mean that "the R5, R6, R7, R8 solution is not recommended"?

I think you mean that your picture shows two R's in parallel for each of R5-R8, and you want people to use 1 R there?

right?
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