lm3886/lm3875

[psychosteve]

does any one know if the lm3886 chip will work on BrianGT's 3875 boards?? i know there is no mute pin hook up, but ill point to point that seperately. cheers for the help, steve.. ..

[demogorgon]

I belive I'v seen that their pin layoute are different from oneanother. (never could get that word right..)

marius

[carlmart]

Originally posted by psychosteve
does any one know if the lm3886 chip will work on BrianGT's 3875 boards?? i know there is no mute pin hook up, but ill point to point that seperately.

I wouldn't advise it. I am not too familiar with the BrianGT layout, so I don't know what he did with the NC (not connected) pins. There are several 3875's NC pins that are used on the 3886. Pins 7 and 8 have different implementation on each chip. Should be a lot of p2p wiring to do, and the pcb shouldn't be that useful.

If I am not wrong Digi001 has some 3886 pcbs to sell. There should be others, as the 3886 is more generally used than the 3875.

Or go completely p2p if you are using single chips instead of bridging or paralleling.


Carlos

[peranders]

A LM3886 will probably pretty good as long as you get the pins right. Some are changed and the "mute" must be connected.

[carlmart]

Originally posted by peranders
A LM3886 will probably pretty good as long as you get the pins right. Some are changed and the "mute" must be connected.

The problem is that to get the pins right you will have to isolate 5 pins from the 3875 pcb. Is it worth the effort?


Carlos

[peranders]

Why can't you get the right IC?

[DrDiode]

Nont do it...the pin outs are different

[richie00boy]

Steve,

The pinouts are totally different.

The ESP 50W chip amp board would do fine. I also know of a vendor getting ready to release a kit/board. Alternatively, I am working on a board and will release the design or do a group buy if enough people are interested and I'm happy with the design.

[planet10]

It has been done... the member doing it isn't using 3875 anymore at all... he likes the 3886 better. I've emailed him this thread so he can chime in...

dave

[Brent Welke]

Actually using a LM3886 in the Brian's board is a nice way to go. I have done it twice. You have to cut one trace on the bottom of the board with a utility blade, add a 10 K resistor (cheap one will do, because it is just for the mute function), and add a couple jumpers, solder one end of R3 (680 ohm) directly to the chip and move one end of the feedback resistor over one pin on the chip.

I have even removed LM3875 chips that were soldered in and replaced with LM3886. The LM3875 chip is destroyed in the process because you have to bend it back and forth until all the pins break off. Apply fresh solder, remove pins then use de-soldering wick to remove the solder from the holes.

Note: Not all pins are used on these chips so if you are having trouble getting a pin into a used hole then check the datasheet to see if you even need that pin.

To me the LM3886 sounds cleaner and quicker in the mids and highs. Not sure about the bass. The LM3875 might have nicer bass, but it was hard to compare with the big difference in sound between the two. Don't get me wrong LM3886 bass is great, but I remember the bass being fuller with LM3875, but that could be because the highs and mids were not so full.

By the way I used the premium kits, BlackGate 1000uF caps and 25 Volt (300VA) transformer.

When I want to build more amps I will continue to use this board with this modification because it is easy and it sounds better (to me, others have said the same). But likely Brian's LM4780 kit/board will be the next one I build. The LM4780 is actually two LM3886s in one chip.

Included is a picture of a LM3886 in a LM3875 board. Sorry for the poor quality.

You see a big solid jumper between two pins. The carbon 10K mute resister (I didn't use 10K, but I suggest you do). The cut trace on the board is where the orange wire in the middle connects.

On the chip, the fedback resistor, one end of this resistor is soldered to the next pin over.

On the top of the board the R3 (680 ohm) resistor has its one closest to the chip removed from the board and soldered directly to a pin on the chip.

I suggest looking at the two datasheet pinouts allong with this post and it will all become clear. Until it is clear don't begin.

The mod appears to be complicated but it is not and the difference in sound is worth it. When I converted a second amp from LM3875 to LM3886 all I had to do was look at the first one, no datasheets.

No pain no gain