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Old 14th November 2004, 07:40 AM   #1
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Default Are LM3875, aka gainclones, chips suitable for a car amp?

So, I'm finally figuring out a SMPS for a car amp that I've been planning to use with some LM3875s that I have, but I have not seen any of these. Would these chips not work well with 4 ohm speakers?
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Old 18th November 2004, 08:21 PM   #2
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Nothing? Nobody has anything to say?
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Old 18th November 2004, 08:45 PM   #3
roibm is offline roibm  Romania
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kinda hard to get an answer to a lot of questions nowadays.
they would be suitable if your speakers are over 4ohm and if you can provide the required voltage, which is not that easy. have a look at the datasheet for the minmum voltage and for the voltage vs impedance vs power graph
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Old 18th November 2004, 10:07 PM   #4
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I used one in my 1987 MB420 -- for newer cars you should really take heed to make sure that the SMPS is well shielded, that the supply lines to the battery have the proper chokes -- you could probably shut down any new microprocessor controlled car with all the RFI which an unshielded SMPS creates.
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Old 18th November 2004, 11:16 PM   #5
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Well, I sure hope so.

I'm currently very happy with my commercial car amps, but I'm thinking about bi-amping everything in the future, and that means that I'll want more channels.

On the drawing board is 8 channels from LM3876/LM3886 chips, which are very similar to the 3875s. I'm planning to use the 3876 chips for tweeters and center channel, and the 3886s for midranges and woofers. Subwoofers will either remain as they are, or be changes over to a beefier diy transistor amp capable of delivering a bit more power to the 4 ohm voice coils.

All speakers are planned to be 4 ohm, but with the bi-amping, I'm hoping that none of them get pushed hard enough to cause a problem.
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Old 20th November 2004, 11:10 AM   #6
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I went with the P3A diy car amp. it is not as simple as LM3875 but the sound quality is good and you have the ability to drive 4 ohm loads with the power.
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Old 20th November 2004, 05:52 PM   #7
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Actually, I looked a little closer and found out that LM3886's are rated for 4 or 8 ohms. LM3875's only have ratings for 4 omhs on the data sheet. Btw, LM3875's actually have a higher power rating than LM3886's contrary to what most people think.

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Originally posted by SupraGuy
Well, I sure hope so.

I'm currently very happy with my commercial car amps, but I'm thinking about bi-amping everything in the future, and that means that I'll want more channels.

On the drawing board is 8 channels from LM3876/LM3886 chips, which are very similar to the 3875s. I'm planning to use the 3876 chips for tweeters and center channel, and the 3886s for midranges and woofers. Subwoofers will either remain as they are, or be changes over to a beefier diy transistor amp capable of delivering a bit more power to the 4 ohm voice coils.

All speakers are planned to be 4 ohm, but with the bi-amping, I'm hoping that none of them get pushed hard enough to cause a problem.
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Old 20th November 2004, 06:31 PM   #8
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at +/- 36V the LM3886 will generate 64.6W and the LM3875 60.6W -- the TF (insulated) version in both require instances a much larger heat sink than the T version.

You can download the design tool at:
http://www.national.com/appinfo/audi...gn_Guide14.xls
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