LM3875 vs. LM3886 vs. LM4780 - Page 2 - diyAudio
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Old 5th February 2005, 02:48 AM   #11
BrianGT is offline BrianGT  United States
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Originally posted by homer09
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).
I saw that too. I am going to try 10,000uF first and see how it works compared to the LM3875 with it's 1,500uF caps.

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Old 6th February 2005, 08:49 AM   #12
indoubt is offline indoubt  Netherlands
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Default 2*10.000uF Vs 4*4.700uF

Brian and others

In stead of adding 2 * 10000uF on the rectifier board is it also possible to change the 1500uF caps for 4700uF caps. The 100uF electrolyte and the 0.1uF ceramic can be directly at the chip pins,

The snubber (1W, 1ohm + 0.1uF film) as wel as the 0.1uF film cap can be at the bottom of the board in the holes previously used for the panasonic FC caps. The leak resistor(2.2Kohm) can be soldered where the V+ and V- are connected to the board.

The 4700uF can be soldered where previously the Black gates could be placed. They are only 26mm dia and 30 mm high (BC components 40V)

From the schematic it looks like it should not be a problem, or am I overlooking something?

People having boards already, having space limitations or want ease of upgrade might be interested
better be indoubt untill you're sure
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Old 6th February 2005, 09:38 AM   #13
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vague testing amp i made for work

1 BrianGT 3875 with carlosfm (that was greeat for this one)
2 BrianGT 3875
3 hardwired 3886
4 hardwired 3886 with carlosfm (i believe i made a mistake here)
hvent tried 7480 yet

thats just the way it sounds to me though. dont use me for a vote.
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Old 7th February 2005, 11:09 PM   #14
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Default LM3886 and LM4780 with 8 ohm speakers

Brian's comment's earlier in this thread, and from reading the datasheets, I am lead to believe that if using 8 ohm speakers, one should stick with LM3875, and stay away from LM3886 and LM4780. Even at higher power levels, the 3875 offers best sound quality. Is that correct?

Brian's previous comments:

"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:

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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Old 8th February 2005, 06:34 AM   #15
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Default LM4780 sound incredible with any load.

I have run 4, 6, and 8 ohm loads on my LM4780s (brians boards) and I can tell you it sounds incredible on every speaker I have tested (4 so far).

I think the parallel 4780s is the best all around option. It gives you maximum flexibility.
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Old 8th February 2005, 11:44 AM   #16
breez is offline breez  Finland
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"it is said to be better due to it's simplicity" doesn't really say anything definitive in my opinion. And could few more pins and a mute function really be detrimental to sound quality? I'd say the reason for a possible qualitative difference is due to something else.
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Old 8th February 2005, 02:59 PM   #17
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Default LM4780 and 8 ohm speakers

When Brian says fort he LM4780:

"With the 2 amps in parallel, each amplifier sees double the output impedence, making this chipamp best for low impedence loads."

... does it mean that 8 ohm speakers are not a good choice for the LM4780?
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Old 8th February 2005, 03:37 PM   #18
BrianGT is offline BrianGT  United States
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Default Re: LM4780 and 8 ohm speakers

Originally posted by ransom peek
When Brian says fort he LM4780:

"With the 2 amps in parallel, each amplifier sees double the output impedence, making this chipamp best for low impedence loads."

... does it mean that 8 ohm speakers are not a good choice for the LM4780?
This just means that each LM3886-equivilant amp inside of the LM4780 (in parallel configuration) would see a 16ohm load with a true 8ohm load. The LM3886 shouldn't complain running a 16ohm load.

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Old 8th February 2005, 08:52 PM   #19
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I am currently comparing a BrianGT 3875 premium to a CarlosFM Regulated 3886 IGC built on modified Digi01 boards.

The Regulated 3886 has the snubberized values between the diodes and the regulator, so it is not a pure CarlosFM regulated IGC. This may or may not be a good idea. Power supply caps are the apexjr.com 12,000uF Nichicon. No buffering on either amp but both have no pot on the input. Both are driven by the same preamp.

I am driving speakers crossed over to a sub 12db at 90Hz

As has been observed, the regulated 3886 is much more accurate. This is clear when playing loud passages. An example is cranking up Dire Straits, Money for Nothing from the Brothers in Arms CD. (Warning, some may not find this song PC unless you realize it is quoting someone they are poking fun at)

This track has strong kick drum and bass in it so is probably pretty demanding on the smallish power supply cap. At the same time though there are many overlayed sounds that come in and out, some of them quite detailed.

On the regulated 3886 the sounds like the distorted synth sounds that come in once in a while or the growly guitar are much more convincing. The whole sound and vocal is much more solid. The subtle cymbal in one part was identifiable on the Reg 3886. It was a tad fuzzy on the 3875 Gainclone and not as convincing.

Same impression with Green Day - American Idiot. This recording has a lot of noise and effects in parts of it, even on the vocals. On a muddy system, it sounds..well..like a muddy clump of sound. On the Regulated 3886 things are pretty distinct and you can hear the reverb and modulation effects on the vocals apart from the overall noise. Still a "wall of sound" type recording on some passages but gives a nice sound to this recording.

So if you like your rock cranked you will likely prefer this over the BrianGT 3875 implementation.

But the BrianGT had advantages. The sound was a bit more ethereal (?). Perhaps this is what people mean by "air". Vocals were less specifically placed which was a nice effect at times. I will come back to this later.

What surprised me was when I played quieter passages.

For example I played a 1964 vinyl recording of Dave Brubeck - Impressions of Japan. (Highly recommended!). On Fujiyama the
piano is much clearer after the note is struck on the Reg 3886. (What a hauntingly beautiful thing to listen to.) On the 3875 Gainclone it is a bit fuzzy in comparison. Same for the delicate cymbal on "The City is Crying". Definitely more delicate and distinct on the Reg 3886.

So I can see wanting to use the Reg 3886 for this type of music when I am really sitting down and focusing on it.

But there is something about the BrianGT 3875 premium that is very appealing, particularly when walking around the room. It may be that that slightly less detail and less distinct positioning is a benefit at times. It also gives an impression of a larger taller soundstage.

So I am not sure that one always wins out over the other. I can see using them both of them at times depending on my mood.

Clearly I need both

The regulated 3886 will probably get the majority of play. Maybe 70/30. But I think there is a place for each.
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Old 9th February 2005, 05:29 AM   #20
ROVSING is offline ROVSING  Denmark
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I have just finished my first GC on brianGT's LM3875 boards and added carlos' snubber with 7200uF on each row, the sound is amazing, I don't think that anybody will be dissappointed over the result of building this.
You will get a lot of good sound, and it is cheap to build.
I have only used cheap components, and i'm very satisfied with the result.
Just go for it !
My personal judgement :

fore the sound.
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