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Old 28th January 2005, 06:30 PM   #1
SRMcGee is offline SRMcGee  United States
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Question LM3875 vs. LM3886 vs. LM4780

Folks:

I have finished four LM3875-based amps using Brian Bell's terrific PCBs and am thrilled with the result. But as I follow the various threads on this website and periodically review Brian's offerings on chipamp.com, I am left with the following question: what are the differences between the various chips, and how do they compare in terms of features, power handling and sonics?

And Brian: consistent with the foregoing, perhaps you could provide a little detail on your website distinguishing your various offerings from each other? Prospective customers (especially newbies such as myself) may want a little direction or advice on which option to choose.

Thanks to all for any insight you can provide.

Regards,
Scott
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Old 28th January 2005, 09:39 PM   #2
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Default Re: LM3875 vs. LM3886 vs. LM4780

Quote:
Originally posted by SRMcGee

Thanks to all for any insight you can provide.

I suggest a forum search. There are at least 10 threads comparing each of these chips to one or the other or both.

Also, perusal of the NSC data sheets for the chips will give you an idea of how they differ technically.
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Old 28th January 2005, 09:52 PM   #3
steenoe is offline steenoe  Denmark
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Quote:
I suggest a forum search.
I guess that would take a lifetime, or so
Suggest you sign up for the new 3886 board and you will propably be walking away with your arms high over your head

Steen.
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Old 29th January 2005, 02:23 AM   #4
BrianGT is offline BrianGT  United States
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Default Re: LM3875 vs. LM3886 vs. LM4780

Quote:
Originally posted by SRMcGee
I have finished four LM3875-based amps using Brian Bell's terrific PCBs and am thrilled with the result. But as I follow the various threads on this website and periodically review Brian's offerings on chipamp.com, I am left with the following question: what are the differences between the various chips, and how do they compare in terms of features, power handling and sonics?

And Brian: consistent with the foregoing, perhaps you could provide a little detail on your website distinguishing your various offerings from each other? Prospective customers (especially newbies such as myself) may want a little direction or advice on which option to choose.
I will need to work on a FAQ (frequently asked questions) section for the website for questions like this. Here is what I see as for the difference:

LM3875 - simplest of the higher power chipamps out there by National, bigger brother to the LM1875. This amp has the fewest pins (5 pins used for +IN, -IN, OUT, V+ and V-). Sonically, it is said to be better due to it's simplicity. As for power, this amp has lower current handling, making it not as suitable for lower impedence loads.

LM3886 - newer chipamp based on the LM3875, with higher current handling and mute functionality. This chip is more capable with 4 impedence loads due to the higher current handling. There are more pins used also (8 pins, extra V+, GND and MUTE input pins).

LM4780 - newest chipamp, with 2 - LM3886 dies inside the larger package. The larger package is has higher thermal power dissipation properties. The pcb that I sell has the 2 LM3886 amps inside wired in parallel, see schematic. With the 2 amps in parallel, each amplifier sees double the output impedence, making this chipamp best for low impedence loads.

Datasheets will show power handling:
LM3875
LM3886
LM4780

As for a higher power solution, it seems like it would be the most sense to put a bridging chip with 2 LM4780 boards, for a setup similar to the BPA200 application note setup.

These are my observations. Sonically, the best amp might depend on how difficult your speakers are to drive. The LM4780 should be considered as 2 - LM3886 in 1 package. In terms of power supplies, the new larger power supply board with 10,000uF (will accept 22,000uF ) per rail and Carlo's snubber design, should also help with more difficult speakers.

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Brian
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Old 4th February 2005, 11:45 AM   #5
G4ME is offline G4ME  United States
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So if the 3886 can handle more current, does that mean you can use higher rail voltages with lower impedances?

Also if the new kit's can handle bigger caps, do you think we could order the 3886 with bigger caps?
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Old 4th February 2005, 12:14 PM   #6
BrianGT is offline BrianGT  United States
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Quote:
Originally posted by G4ME
So if the 3886 can handle more current, does that mean you can use higher rail voltages with lower impedances?

Also if the new kit's can handle bigger caps, do you think we could order the 3886 with bigger caps?
The LM3886 kits that I am putting together now will all include the new "snubberized" power supply with 10,000uF caps. The board will accept up to 22,000uF caps (largest 35mm diameter cap I could find in the catalog).

As for the LM3886 current handling, the datasheet goes over this:
http://www.national.com/ds.cgi/LM/LM3886.pdf

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Brian
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Old 4th February 2005, 03:33 PM   #7
loong is offline loong  United Kingdom
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In my case of having small listening room ( ~3 x 4m) and have +88 db/w/m speakers, the bass and loundness of 25W from the LM3875 (even 20W from the LM1875) plenty more than enough for me.

More bass doesn't means better ,
Sound different doesn't means better,
It depends on your taste. your listening room, your music you listen, and your speakers.

To me, I likely stop DIY for a while to enjoy the MUSIC!

NAD 521iBBE + LM3875(25W) + 88 dB/w/m speakers + tons of CDs!

Cheer!
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Old 4th February 2005, 03:38 PM   #8
G4ME is offline G4ME  United States
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would it be an option to order the 3886 with 22,000uF, or will we have to pick them up separately, and toss the 10,000uF
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Old 4th February 2005, 04:24 PM   #9
BrianGT is offline BrianGT  United States
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Quote:
Originally posted by G4ME
would it be an option to order the 3886 with 22,000uF, or will we have to pick them up separately, and toss the 10,000uF
I could possibly offer these as an upgrade option. The main issue with the 22,000uF caps is the height. The diameter of both of them is 35mm, but the height of the 10,000uF is 30mm (1.2"), while the 22,000uF caps are 50mm tall (2"). If 3 more people express interest in the larger caps, I can modify the webpage to offer these as an upgrade option. (it would cost about $4 extra per cap given the price difference and the number of parts I am ordering)

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Brian
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Old 5th February 2005, 01:25 AM   #10
homer09 is offline homer09  Canada
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will 22 000 provide an improvement? i believe i read somewhere (from memory, dont kill me if im wrong) that carlos said more than 10 000 had no gain in sonics (for a dual bridge anyway).
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