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AudioSector-chip amp kits, dacs, chassis

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#1,503
alienman said:
Hi, I have a question about using a center-tapped trafo with the lm3875 kit, as none of my local suppliers has anything with dual secondaries. I'm wondering which method is correct, as posted here: http://www.diyaudio.com/forums/showthread.php?postid=548382#post548382. I'd prefer to use Sherman's method, as I really have no use for 12 extra diodes 🙂
Click to expand...

Sherman' method will work fine, although it's not exactly the same as dual secondaries.


Destroyer OS. said:
I need to ask once more, will the 24v x 2 400VA (BG caps recommended in use) have any problems with impedence of a Squeeze Box?
Click to expand...

I don't see a connection between impedance of a squeezbox and voltage supply of the amp? 2 x 24V is a good choice for the supply and should work well with most speakers.
 
#1,505
Hi Peter!

I built your LM3875 some time ago and it still gives me a great deal of listening pleasure a year down the line. I'm using 2 x 1000uF Black Gate standards at the bridge (PSU unit is in a seperate box), and 2 x 100uF Elna Silmics on each amp board (I will upgrade to Black Gate Ns at some point)... in other words it's a cut price Patek 😉

Just wondering what your current reference is at present? Is it still 1000uF at bridge and 100uF on amp boards?

Many thanks.

- John
 
#1,506
Let me just jump in here and reiterate how great MY premium Audiosector LM3875 amp(s) sound as well.

I've lived with this thing for some time now, and swap it in and out against very good 2A3, EL34, Class D and conventional amps and am always stunned at the quality of the little amp that could when I plug it back in.

Masterful.

-Rob
 

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#1,514
I have a question about heat sinking. I am building up 3875 kit. Actually it has been up and running for about a year and is now facing being enclosed. I found amongst my pile of scraps and parts a piece of 6" OD 1" wall pipe. The steel is really low grade, (sparks and flaming chips when it is cut) but it does clean up nice. So, I was wondering if I will have sufficient heat sinking if I mount the chips to a piece of .375" plate that is press fit into a 6" OD 1" wall 5" tall piece of pipe. Initially I was only going to house the power supply in the pipe, but I have realized that I have room for all of it. I will probably shield the transformer with some copper foil I have kicking around. Here is a pic of the parts and pipe.

Thanks

DaveM
 
#1,516
It will probably work, but thermal release efficiency will be compromised by steel as a material, and also by substantial mass of the whole thing. Depending on how much you will be pushing the amps (volume and load), it may get only slightly warm, or may reach 40-50 deg and stay there. I was using brass rod to mount the chip (2" dia , 8" long and it was acting as heat tank, storing thermal energy, but not releasing)

Since you have it already made, it's worth trying anyway.
 
#1,517
I have some brass bar stock sitting around as well. I think I will add a piece of brass to the top cover and mount the chips to the brass. At least this way the heat transfer to the brass is pretty good and the thermal contact area to the steel will be vastly larger than the chip surface. It can't do anything but help.

Thanks for the insight.

DaveM
 
#1,520
Looking a bit closer at that chart, I will be better off using aluminum with a good bit of thermal paste between the steel and aluminum to prevent issues with the dissimilar metals. I always thought that brass was a better conductor than aluminum. That was defiantly a misconception.

Thanks

Dave
 
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