LM4780 pcb layout and others

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#202
BrianGT said:


...
The LM4780 pcb that is currently looking to become a group order is essentially 2 parallel LM3875 channels, so if you bridge them, it will be much tolerant of low impedence loads.
...

Brian
Click to expand...

Now that's a bit wrong isn't it? The LM4780 is more like 2 LM3886 instead of 2 LM3875. Just look in the datasheets. The output current limit for the LM3886 and the LM4780 is typical 11.5A, while the LM3875 it's only 6A.
 
#203
moamps said:
.....single layer design with a little pins rearrangement ...
Click to expand...

Looks good for us board-etchers at home. Are you planning to post the CAM output from Eagle in postscript or PDF form for us to use, or are you keeping this one-sided layout close to your heart? 🙂

Same goes for BrianGT/Peter, I noticed Brian posted the CAM output for us in PDF format earlier, but changed the design to add heat relief pads. Will we be seeing another PDF for the at-home etching crowd?

Just curious...

Cheers,
Chris
 
#204
CrisTUFR said:


Looks good for us board-etchers at home. Are you planning to post the CAM output from Eagle in postscript or PDF form for us to use, or are you keeping this one-sided layout close to your heart? 🙂

Same goes for BrianGT/Peter, I noticed Brian posted the CAM output for us in PDF format earlier, but changed the design to add heat relief pads. Will we be seeing another PDF for the at-home etching crowd?

Just curious...

Cheers,
Chris
Click to expand...

I will see what I can do. I am making some small changes to the layout now. I will most likely post a pdf of the files.

--
Brian
 
#208
BrianGT said:


Here is a new version of the PDF with the heat relief traces, and a slightly smaller pcb. You will also see that there are no vias on the pcb.
Click to expand...


Thanks for the file. I will download it at home and muck around. It, too, may be built (and tested) in the next few days. 🙂

Again, make sure you print this at 100%, and do not allow for Acrobat to scale the image.
Click to expand...

Acrobat?! Ha! I use Preview for OSX. 😉

I always test layouts on paper (by poking components through) before doing any etching whatsoever. 🙂

Cheers,

Chris
 
#209
CrisTUFR said:


Thanks for the file. I will download it at home and muck around. It, too, may be built (and tested) in the next few days. 🙂



Acrobat?! Ha! I use Preview for OSX. 😉

I always test layouts on paper (by poking components through) before doing any etching whatsoever. 🙂

Cheers,

Chris
Click to expand...

Well, just make sure that the outline on the layout measures 2.9" x 1.4" when you print it out.

Good luck,

--
Brian
 
#213
CrisTUFR said:
What type of resistors do you guys use for R8 and R9? I've always used huge 5W sandbar resistors since that's all I could find in a pinch...

Can I go as low as 1W, or do you guys suggest something bigger? Also, is quality a concern in this area?

Chris
Click to expand...

I have mills MRA 3W resistors that I picked up a while back from a group buy. There are what I was going to use.

The Dale 3W ones are similar (RS2B):
http://www.mouser.com/catalog/618/398.pdf

--
Brian
 
#216
I was talking about high power, low value resistors, the ones used in Alephs.

They could be used as well here, in place of 0.22ohm resistors.



I did some listening comparisons today again, as well exchanged my observations with some audiophile friends, who listened for a while to my LM4780 amp, and LM4780 is not exactly same sounding as LM3875. The latter produces more "magic", there is more air, extention in highs and more 3-D sound. LM4780 sounds more average by comparison. Some of it may be caused by slightly different implementation (chassis built and so on), but overall, I wouldn't trade my LM3875 amp for the more powerful chip. It still may be good as higher power amp (for subs), but when it comes to midrange clarity, highs extention and more lively presentation, LM3875 can't be bettered yet.
 
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