my first try at a LM3886 layout, any comments/suggestions?

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#121
Upupa Epops said:
To homer : In my amp with LM 4780 I have 200 VA toroidal transformer with 2*25 V AC. Output power is ( by one channel driven ) little bit below 80 W/ 4 ohm. By both channels driven is it 2*60 W / 4 Ohm, 2*45 W/ 8 Ohm and in bridge configuration 120 W / 8 Ohm. With cca 300 VA transformer and the same voltage, you can to get app. 10 - 15 % more wattage, but it will be not for this chip safety, so you must use lower voltage.
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Question: Do you have enough cooling for say 2*60W at 4 ohms? ~120W heat dissipation is not one of the smallest tasks.
 
#122
m0tion said:
Isn't there some reasonable way to calculate the amount of power needed?
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Determine the how much power per channel you need and at what load. Then you can make out the current and voltage requirements (which determine what kind of trafo is the minimum). For voltage you should consider diode loss and the headroom the chip needs (usually few volts, check datasheet).
 
#124
Dear Pavel (Upupa),

I'm learning... on building amps. In fact, my knowledge is very limited to basic ohm's law till now... (I already forgot the thevenin theories which I just got as several session during my university time, 15 years ago)

Doesn't the RMS power efficency loss (from PSu to amp output) on the amp circuit can become a good reason to have an "enough" power capacity start from the transformer itself?

Based on 60% efficency, if I'm expecting to be able to sustain 4 Amp to the output, shouldn't Ibe able to sustain 4/0.60, which is 6.66 Amp... ?

Designing up to the worst case scenario is always be expensive...

But I believe that is one of the reason that some people go to DIY-ing... have a non-compromised performance...?

REgards,
---
David
 
#126
edjosh23 said:
I saw the group buy for 100uf/35v Elna SILMIC II caps for $.30 a piece. Is 35v too low? Does it depend on the transformer? Would 50v or higher be better? I read that these were nicer than BG, but it was from a very biassed article. Any thoughts on these caps?

link to group buy

Thanks,

Josh
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You will want 50v. If they are in the same diameter, I could add them to the kits instead of the Panasonic FC caps. They don't seem to cost too much more.

EDIT: They are a larger diameter, the 100uF 50v ones, but the 47uF 50v ones would fit.

--
Brian
 
#130
m0tion said:
Can we pre-orderers get a status update?
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Boards have shipped out, and I should receive them on Friday, and will start shipping out the kits as soon as possible.

I will take pictures of the boards when I get them.

On a side note, I ordered the next batch of the LM3875 rev.3 boards and posted details on my webpage:
http://www.chipamp.com/lm3875.shtml
The lm3875 rev.3 boards will ship to me within 2 weeks, and they will also be compatible with the snubber power supply.

--
Brian
 
#133
m0tion said:
Ahh! Well, you know I'm happy to see this. Any chance on getting some LM3886 board shots as well? Thanks for your great effort!
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I will take some new LM3886 pictures next. I found my battery charger to my old digital camera, and took some better pictures and posted them here:
http://www.briangt.com/gallery/snubber

Here is one for those too lazy to go through the gallery:
An externally hosted image should be here but it was not working when we last tested it.


Sorry for the delay, but my parents are in town visiting me this weekend, and I haven't had much time to work on this stuff yet. I tested the power supply board tonight, and it seems to work good. I am building up the LM3886 boards now to create a working amp.

Stay tuned for more pictures,

I am creating a webpage now to add to the website, so that I can also sell just the power supply board with parts, so that people can upgrade their existing LM3875/LM4780 setups.

--
Brian
 
#137
I assembled the boards, and I will wire them up to the power supply tomorrow and try them out. I added more pictures to my gallery. I will work these into my new assembly manual that I am working on.

Assembled boards:
An externally hosted image should be here but it was not working when we last tested it.


I am glad that I can use my old camera for pictures, interesting how a 3 year old 2.6 megapixel camera takes better pictures than my new 4 megapixel camera.

Also, I updated the order page to now say "blue LEDs". I am sorry if anyone is disappointed that I won't be offering red LEDs with the kits any more. I will offer a 10k resistor and a 22.1k resistor for putting in series with the LED to select your desired brightness. The massively bright pictures in the gallery were taken with a 4 second exposure, so the LED isn't really that bright. I was just playing around with my camera and the lights turned down, so don't think that this is an ultra bright LED. It is actually the second darkest blue LED that digikey sold. (310 mcd, where range = 180-880 for the 3mm T1 size). The LED can be placed on the pcb, or wired off board to the front of your chassis.

--
Brian
 
#139
interesting how a 3 year old 2.6 megapixel camera takes better pictures than my new 4 megapixel camera.

Good digital pictures is a combination of megapixels and optics many megapixels doesn't do it alone.
Here at work i got an old camera 1.6 megapixels with Zeiss optics it takes terrific pictures, optics are at least 50 % of a good picture...😉
 
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