ebay lm1875 pcb

[asuslover]

hello folks !
I was going to buy an lm1875 mini ref pcb from Linuxguru, but he is very difficult to be reached, so i got this pcb from ebay....
I dont have a schematic, i would love to know if any of you guys tried this pcb before.

 

[Ian Finch]

There are a few kits similar to the above example. They all have a problem with closely packed sections that run too close together and often the output is within 2cm of the input which causes problems with distortion and stability. Sure, it minimises cost and makes it compact that way but there are usually more important requirements for our DIY projects.

I'm not endorsing the example linked here, as I haven't used one but you get the picture of what may be considered better layout practice for optimum, clean performance: Assembled Stereo 40W LM1875 SK3875 Audio Integrated Amplifier Board | eBay

 

[asuslover]

thanks Ian, i do not believe that is a perfect layout , but I didnt have the too many lm1875 pcb options .
The one you pointed to me looks good, but its assembled , and it's actually very confusing, it is called sk 3875 but it is using lm1875 chips not lm3875 as , i think, most of us would believe....

 

[cowanaudio]

Here's the Schematic

View attachment LM1875_Current_FB_Board.pdf

I bought one of those boards and drew out the schematic. It has current FB.

 

[asuslover]

Thanks a lot,
this is what I got , maybe a little different , but close to yours...
its not so important the schematic, I am more curious if the amplifier works .

 

[AndrewT]

Asu,
check your sch.
There is no bias current into/out of the +IN pin.

I don't know what the 10k and the two 12k are for.

 

[Ian Finch]

lm1875 chips not lm3875

If you look closely at the PCB, the Chips are mounted flat below the board, as with many flatpack transistor builds. It's actually quite a delicate operation to re-form the pins without fracturing them where they were sharply kinked, in order to mount them flat.

Making it easier, SK3875 are cloned LM1875 chips but they have unformed pins and full encapsulation to simplify the mounting procedure, as you see in the pic here and with larger chips like LM3886, LM3875 that also come in isolated packages.

 

[asuslover]

you are right about this chip, difficult to find data about it , but it does exists.
the chip name , sk3875 , makes me thinking about the lm 3875, that's all.
But i never heard about it until now, as far i understood, it is made for sony by national.