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-   -   I'm liking the LM3875... (http://www.diyaudio.com/forums/chip-amps/193113-im-liking-lm3875.html)

Boscoe 23rd July 2011 04:56 PM

I'm liking the LM3875...
 
Just thought I would share my opinion! Great sounding, crystal clear warm smooth bass. Just say it's great just need a little more power!

Using 300VA 18Vac transformer, 2 X 10,000uF caps the chipamp boards.

http://i550.photobucket.com/albums/i...9/f95619a3.jpg

http://i550.photobucket.com/albums/i...9/88085ba6.jpg

http://i550.photobucket.com/albums/i...9/aeb98f82.jpg

! 25th July 2011 01:10 AM

That looks extremely durable.

I'm suspecting you don't need that heatsink at all, with such a beefy case you could just mount the LM3875's on the side walls of the case, or probably even the back (or would it be front?) wall.

Boscoe 25th July 2011 06:33 AM

They get pretty warm when playin music full though so I prob wouldn't want to risk it, I don't have any ventilation with it you see.

AndrewT 25th July 2011 09:45 AM

Quote:

Originally Posted by Boscoe (Post 2649228)
They get pretty warm.............. I don't have any ventilation with it

you're telling us that all the contents (resistors, capacitors, semiconductors, etc) are being slowly cooked until one or more fail !

ttan98 25th July 2011 10:18 AM

Hi,

I use CPU heatsink and mine does NOT get hot just warm, I use medium to high efficient speakers, >=88dB. There is a fan attached to the heat sink I use it sometimes. My P/S is +- 34Vdc

jemraid 25th July 2011 10:37 AM

Dear Boscoe,

Very nice build it looks really good :-)

Just as a matter of interest I made an IGC to Thorstens circuit in 2004;

http://i35.tinypic.com/aea42f.jpg

The chips are on a couple of pieces of alloy bar and the rest of the components just proud of it held there by their own leads.

It still works fine, but [there's always one] my new NIGC with CarlosFM's power supply sounds much better!

Regards - Jim

sunvio 25th July 2011 10:44 AM

Quote:

Originally Posted by jemraid (Post 2649384)
Dear Boscoe,

Very nice build it looks really good :-)

Just as a matter of interest I made an IGC to Thorstens circuit in 2004;

http://i35.tinypic.com/aea42f.jpg

The chips are on a couple of pieces of alloy bar and the rest of the components just proud of it held there by their own leads.

It still works fine, but [there's always one] my new NIGC with CarlosFM's power supply sounds much better!

Regards - Jim

其实走线的布局可以再合理些.慢慢来你会做的很好的。虽然可能您看不懂我在说什么...... .

其实因为我也不会说英语呀.唉.

:cop: google translate

In fact, the layout of the alignment can be optimised. Take your time you will do well. Although maybe you do not understand what I mean .......

In fact, because I do not speak English Yeah. Oh.



请张贴在英语。你可以写中国的语言,如果有一个英语翻译。
please post in english. You can write chinese language if there is an english translation too.
:cop:

pinkmouse 25th July 2011 10:53 AM

:cop:

English please Sunvio.

johnr66 25th July 2011 03:26 PM

Play music at high levels and I bet those alloy bars get too hot to touch. Sure the thermal mass of the bars will make it take longer to warm up, but they will get sizzling hot. Heat is the enemy of electronics. I oversize the heatsinks and be sure there is plenty of ventilation for convective cooling (heatsink with big fins and cabinet slots).

! 25th July 2011 04:32 PM

It gets hot because you have it entirely enclosed, once the top is on of course... or am I wrong, does the bottom panel under the heatsink have large opening(s) and the top as well for a passive chimney effect? If not, that is another thing to consider to reduce heat buildup.

If you 'sink to the cabinet instead, the outer surface is exposed to room air and with reasonable good fitting panels the heat would be sunk from sides to front, back, top and bottom too... which could effectively be as good if not a better heatsink. Further, the surface area of all those case panels is not only similar but probably greater than that of the heatsink itself.

I should pause and mention I am assuming they are aluminum or another reasonably thermally conductive alloy, which they look to be.

People have built amps with higher output (rails at higher voltage, I don't know your load impedance) and had success with lesser heatsinking, and as AndrewT mentioned, it gets more of the heat out of the cabinet so the other parts run cooler.


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