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Paswa 2nd April 2008 08:46 AM

LM1875 PCB, Which To Use
LM1875, you know, I know, it's a great IC. I'm building a 5 channel gainclone with 5 LM1875. There are many PCBs. But what to use?

PCB #1

PCB #2

PCB #3

PCB #4

Now tell me, which is the best PCB among these PCBs. You can add more PCBs to the list.

AndrewT 2nd April 2008 09:22 AM

The 1875 schematic shows inverting topology with 100k to 200k on the inverting input and zero impedance on the non-inverting input. This will give an output offset. If you add 100k to the non-inverting input connection, to reduce the offset, it may be too noisy.
The input impedance is only 10k and that 1uF gives a high pass filter of just 10mS. Again a poor component choice.
Finally, why do a rail splitter when it's far easier to use single rail supply and capacitor couple the speaker?

Nordic 2nd April 2008 10:04 AM

Very clever gentleman, but if you look at the boards carefully you will see that he sacrifices many needed subcircuits with the goal of makeing as small as possible amps.... you should see some of his headphone amps...

BWRX 2nd April 2008 02:48 PM

Re: LM1875 PCB, Which To Use

Originally posted by Paswa
PCB #2

That's my pcb from the Mini LM1875 design thread. It hasn't even been made yet!

Paswa 2nd April 2008 03:21 PM

what about This pcb. I made it and it was corrected and revisioned by many diy members

danielwritesbac 3rd April 2008 02:54 AM

Paswa, your design looks quite useful. If I had that board, I would change the R0 to R8. And, I would remove the diodes and use a seperate power supply board.

madisonears 3rd April 2008 04:44 AM

Yes, LM1875 is a great chip, but the biggest implementation problem is that there are almost NO boards available. Lots of people make their own boards or hardwire the amp.

One of the few I could find for sale is from Quality Kits, and, even at just $13 each, it's hardly worth it. The components included in the kit are the very cheapest available, the PCB layout is not a good design, and the board itself is not very high quality. The amp built from the kit sounds awful. I have been experimenting with this kit, trying to turn it into something better, and I'm very close now. I threw away almost all the supplied parts and carved up the PCB.

It sure would be a lot easier if someone made a board that had a good design to begin with instead of having to buy and mangle a board to get a decent layout.

ESP sells boards, but I'm not crazy about his layout, either.

The nicest layout of a board I've seen yet is the one Nordic posted a long time ago in another LM1875 thread. I don't know if it's available for sale. Nordic, you never answered my e-mail to you, asking about that board. I would pay good money to get my hands on a couple of them.

Tom E

danielwritesbac 3rd April 2008 05:40 AM

Nordic's Amp
Yes, Nordic's amp looks very nice. Its here:

Nordic 3rd April 2008 06:54 AM

Haha I have such a horribly short memory (result of a car accident), I have forgotten about that board again....

Here is a later version, the one I posted was just to illustrate the concept...
If size is an issue we can always leave out the fuses and make them offboard, it will also reduce the cost of PCB significantly...

P.S. please forgive the silkscreen, I see it is not correct yet...

Tom, My appologies, I must have missed your e-mail... (I do searchengine submissions part time), which brings me a deluge of spam every day...

Paswa 3rd April 2008 07:22 AM

2 Attachment(s)
nordic, your PCB is very very good. Can you please share the silkscreen and the bottom copper layer's high resolution image? That I (or anyone who wanna build 1875 chipampi baby) can directly make PCB. I'm just building my DIY audio amp and ain't any commercial use.
Please nordic, please gimme the silkscreen and the bottom copper layer's high resolution image.

I made a PCB of 1875 toooo...see it

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