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Old 8th January 2002, 12:36 AM   #1
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Default LM3876 amp info needed

Hi! I was looking into building an amp from the LM3876 power amp chip. I am just looking to find somthing to drive a set of subs in my car, or even just play with. I figured that the IC might be a little easier to work with than the FET family of transistors.

I planned on running one amp and one sub on the left channel of my preamp out, and one amp and one sub on my right channel of the preamp out. My subs aren't that big wattage wize, so I figured that the 40 or 50W would be good.

There is still one problem. The schematic on the ESP site that I might like to use calls for like +/- 35 volts, and my car has +12. could I run the amp on 12 volts? or would it be possible for a voltage regulator to boost the voltage up to 35V? I am out of ideas. My electronics teacher said that it would be best to build an inverter, run it thru a transformer, then rectify it to get the desired voltage. Would this really be the easiest way?

Whell, Thankyou in advance for the help!
Jude
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Old 8th January 2002, 01:00 AM   #2
blmn is offline blmn  Brazil
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Jude

Why don't you see the project that I told you in other thread? It's a $20 book.

The power supply is capable to feed two 75W amps at +/- 36V regulated output. You can make just the power supply. There is the complete project there, inclunding PCB drawings.

You can't achieve the power you want feeding the amp directly from the battery, and the solution of you teacher seems to me a little strange, and with some problems.

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Old 8th January 2002, 01:06 AM   #3
blmn is offline blmn  Brazil
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There is another solution for your question, but I think it will be not so good.

There are some chips designed for use in automotive applications from Thomsom and other brands. See at www.st.com and look for Ic amps for automotive applications. They have power at this range (40W or 50W), bridged, but the distortion will be higher than in a design using high voltage values.

regards
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Old 8th January 2002, 01:17 AM   #4
lohk is offline lohk  Europe
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As far as I know all car amps with a bit more power use internal power inverters which boost up the voltage. Thats why they use so much current!
There should be lots of links in the net.

Your LM chip will not work with a single 12V supply.

There is another possible link for a single ended class A car amp:
http://www.geocities.com/ResearchTri...car/index.html
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Old 8th January 2002, 01:52 AM   #5
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Default allrite....

k....

"blmn".. I havn't got around to the library yet to see if they have it. I figured that if I could use an IC, it might be able to take a smaller voltage. thankyou for posting the other link. I still might check out the book you suigjested. my teacher is really odd..

"lohk" .. thankyou for posting the link. I will have to take a look.

thankyou.
Jude
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Old 8th January 2002, 02:12 AM   #6
blmn is offline blmn  Brazil
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Jude,

You can make just the power supply and use it with the LM3876 amp. It's easier than the original amplifier section to make, they are independent modules in the original article.

regards,
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Old 8th January 2002, 02:24 AM   #7
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Jude the reality is that if you want decent sound for those subs you cant do it with only 12V .... you will need to construct/buy a switching power supply so that you can have decent voltage rails to use for the amps.
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Old 8th January 2002, 12:07 PM   #8
blmn is offline blmn  Brazil
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Jude

I agree with Audiofreak, the best option is, as I told you before, making a SMPS power supply to achieve the power levels needed without high amounts of distortion and other correlated problems, but, you canīt imagine how loud could an amplifier be even at 12V supply.

regards
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Old 8th January 2002, 12:19 PM   #9
subwo1 is offline subwo1  United States
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One fairlly easy option you may consider is to take one of those ubiquitous 12V to 120VAC converters (commonly called an inverter) and run into a suitable 60Hz transformer, rectify, and filter it.
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http://groups.yahoo.com/group/switchmode/
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Old 8th January 2002, 12:24 PM   #10
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You could do that but efficiency would be absolutely terrible.
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