"The Wire AMP" Class A/AB Power Amplifier based on the LME49830 with Lateral Mosfets - Page 61 - diyAudio
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Old 18th January 2012, 04:13 PM   #601
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Quote:
Originally Posted by AndrewT View Post
The heatsinks do not dissipate as much heat when the devices are located in the upper half of the backplate.
For best dissipation capacity, locate (a single row of) devices at ~ 40% of height up from bottom.
.." - Where To Mount Transistors
Since heat rises by convection, one might think that mounting the transistors on the bottom of the heatsink might improve thermal performance. This is incorrect, and will actually cause the devices to run hotter. Aluminium is an excellent conductor of heat, and the idea is to ensure that the transistors are mounted in such a way that each has sufficient clearance from the others, and they are close to the GEOMETRIC CENTRE of the sink..."
ESP - Heatsink design and transistor mounting
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Old 18th January 2012, 05:11 PM   #602
IanAS is offline IanAS  England
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On the fined side, the passing air is carrying heat upwards and increasing in it's heat, absorbing less heat from the top, ergo, making the top of the heat sink warmer. Hence mounting the hot spot (the transistors) lower. Clearly this is going to be of no significance on a 2U heat sink. I don't know what height of heat sink it will start to be an effect. A friends 12 inch tall heat sinks are hot all over and the eight TO3P are horizontal across the centre.

Last edited by IanAS; 18th January 2012 at 05:17 PM.
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Old 18th January 2012, 05:42 PM   #603
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I will mount my boards little below the centre of HS. Height of HS will be 5U.
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Old 18th January 2012, 06:17 PM   #604
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by dyolFkniP View Post
.." - Where To Mount Transistors
Since heat rises by convection, one might think that mounting the transistors on the bottom of the heatsink might improve thermal performance. This is incorrect, and will actually cause the devices to run hotter.
Up to here ESP is correct
Quote:
.... and they are close to the GEOMETRIC CENTRE of the sink..."
and this bit is completely wrong.
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Old 20th January 2012, 01:57 AM   #605
opc is offline opc  Canada
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Default Mosfet Upset

Hi Guys,

Well, everything was going so well, and earlier this week I hit a very big snag with the kits. I got a note from Richardson RFPD telling me that the lateral mosfets I ordered were apparently impacted by the flooding in Thailand and are not going to be available until March 22nd.

I phoned my contact at Semelab and I was informed that this is indeed the case, and that there is a global shortage of all dual-die lateral mosfets (since they’re all diffused in the same place). I was also informed that they would do their absolute best to bring that date in as much as possible. I’m eagerly awaiting news from them.

This obviously puts me in a very awkward position where I’m holding a lot of everyone’s money, a lot of inventory in parts, and I can’t close off the project.

For the record, I had ordered and paid for the parts from Richardson RFPD on the 14th of December, and was promised a 3 week lead time. I verified with them on January 3rd that the order was ready to go, and was assured the parts would ship out to me that Friday (Jan 6th). It wasn’t until Jan 17th that I got a confirmation that the mosfets would not be shipped to me until March. I don’t know why they did what they did, but they really let me down, and by extension, all of you.

So I’m asking everyone here… what’s the best path forward? I’d like to suggest the following in order of preference:

1. I ship out all kits as they are now without the mosfets. That way people can get their builds underway and hopefully be ready for the mosfets when they arrive in March. At that time I will ship everyone their mosfets via letter mail which is very low cost ($2 in Canada, $4 in the US and $6 overseas). This presents significantly more work for me (twice the number of packages to mail) but seems like the most equitable option to everyone.

2. If anyone feels like hanging tight until March, then I can just wait until they arrive and ship everything together. This presents less work for me, but seems quite unfair to those who have large orders, or those who have headphone amps in their orders and want to get building. Some people have orders that are over $1000 and I know that if I were them, I would want my stuff!

3. Everyone agrees to remove the mosfets from the GB, and I ship the kits as they are to everyone without fets. Refunds would be issued for the mosfets, and everyone would be responsible for sourcing their own parts.

4. I refund everyone their money and risk losing a fortune if people drop out between now and then. (I'm not too keen on this option )

The last alternative I can think of is if someone here can find a source for these parts. At this point I would be willing to take a loss just for the sake of shipping completed kits all at once, so even if they’re a few dollars over $10 a fet I can live with that.

Here are the part numbers. They are all the exact same to the best of my knowledge (except the last two):

P-Channel

“Pro Audio” ACD103PDD
“Semelab” ALF16P20W
“Exicon” ECW20P20Z
“Magnatec” BUZ906DP
“Magnatec” BUZ907DP – higher voltage
“Magnatec” BUZ908DP – higher voltage

N-Channel

“Pro Audio” ACD103PDD
“Semelab” ALF16P20W
“Exicon” ECW20P20Z
“Magnatec” BUZ906DP
“Magnatec” BUZ907DP – higher voltage
“Magnatec” BUZ908DP – higher voltage

I have searched high and low, and called every distributor listed on their website, but nobody is holding stock. Maybe one of you (especially someone in the UK) might have better luck.

Please let me know what you guys think and what each of you would like to do. Again, this isn’t the end of the world, and everyone will get mosfets by the end of march at the latest, but at this point it looks like we’re going to have to wait.

Regards,
Owen
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Old 20th January 2012, 02:27 AM   #606
pchw is offline pchw  United States
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Hi Owen,

#2 is fine with me.

Cheers,
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Old 20th January 2012, 03:13 AM   #607
glt is offline glt  United States
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#2 as well for me. Thanks for all your hard work.
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Old 20th January 2012, 04:09 AM   #608
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#2 is fine with me as well Owen. I know personally that fate can really screwup the best plans and dreams. I can wait another month or 2.

john
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Old 20th January 2012, 05:32 AM   #609
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I don't care, I'll be fine with every your decision. In the end, all that matter is that "The Wire" will push my speakers hard.
You already did bloody job with everything you served us.
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Old 20th January 2012, 06:00 AM   #610
kiwik is offline kiwik  Estonia
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Option2 is fine for me.
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