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Old 16th July 2006, 10:44 PM   #1
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Default chip for a subwoofer amp (~20w)?

wich chip do you recomend for that kind of power on a small subwoofer? lm1875? some tda or stk?? thanks.
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Old 17th July 2006, 04:32 AM   #2
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20 watts isn't much for a sub, what are you tring to make it for? first project? computer system? just for the heck of it?

Anyways.... STK4122 is a 15W + 15W chip, you can bridge it and get 30W, only requires a + 20V supply too.
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Old 17th July 2006, 06:22 AM   #3
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TDA 2040W, TDA 2050W
would be my recommendation from what I've used but I have never tried as a sub amp specifically.

LM3875 is a good chip also but has more output capablity then your asking for. You could also use lower supply rails.
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Old 22nd July 2006, 02:20 AM   #4
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i know it's not a lot of power, but it's for a small sub that will be matched with a 6w+6w system i use with a 14" TV.
thanks for the recomendations. the bridged stk sound ok, but i guess i'll be using a lm3875 with low power supplies, i like the protection circuits the LM line include. what do you think of a LM1875 for this purpose?
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Old 26th July 2006, 09:21 AM   #5
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Default lm1875

lm1875 can output 20W with +/- 25V power supply when the impendence of speaker is 8_ohm. This IC is the most popular one
that use in multimidea speakers for computer. It's really a nice IC that I had used it for more than 15 years.
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Old 26th July 2006, 04:16 PM   #6
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thanks a lot.
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Old 14th November 2006, 12:45 AM   #7
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using a LM1875, single supply 32v, on a 4ohm load, how much power can i get out of it? how much power must the supply be able to deliver?

thanks a lot.

(national datasheet isn't very complete when it comes to 4 ohm loads)
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Old 14th November 2006, 01:06 AM   #8
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20w is a very, very generous maximum.

I would reccomend a LM3875. Just keep the gain moderately low from your input volume control, and you're set.
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Old 14th November 2006, 01:31 AM   #9
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If you want to use some of the National parts in the Overture line then use the Design Guide to do some basic calculations. It can be found on this page: http://www.national.com/appinfo/audio/

Middle column, near the bottom. Will give you some good info. The LM1875 is not in the list but the LM3875 is.

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Old 14th November 2006, 06:39 AM   #10
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Small bass drivers normaly goes into small sealed box, which normaly requires alot of power to fight the inherent inefficiency...

I would also say try the LM3875 chip at least, as long as you have an 8 ohm woofer. it is extremely easy with stripboard/veroboard. break off all but the 5 pins you need.
bend the first leg so it goesto the row next to the chip housing leaving the strip between the +V and output pins as the ground strip... one tiny wire will go from there to the connection on pin 8 or 7 depending on inverted or not..., the pin on the far end also needs to be bent very slightly to go into the hole on the outside of where you thought it would go (similar to first pin)
Its very easy, MUCH easier and more solid than P2P by a long stretch.

very easy to swap between inverted and onon as pin 7 and 8 sits niceley to one side... only need to change the resistors, and attach lead to ground plane to th right pin's components....
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