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Old 6th January 2005, 09:40 AM   #1
jsd is offline jsd  United States
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Default Lm4752?

I'm almost done building a pair of speakers for my PC using 2 4.5" Vifa mids (PE # 299-495) and Dayton 3/4" dome tweeters (275-035) in a ported enclosure. There will also be a sub with two Dayton 8" DVC woofers, and I'll be using 24dB/octave active filters.

In an effort to keep the amplifier design simple, I was looking through National's site, and found the LM4752. It's a stereo chip, and with a 24VDC supply, they rate it at 11w into a 4 ohm load. The power seems reasonable enough for the intended purpose.

Has anyone used this chip? Any comments on sound quality? I realize I'll have to use output capacitors, will using something cheap like Nichicon VR caps be seriously detrimental to sound quality?

Each sub has two 8ohm voice coils, I was going to wire them in parallel and use a 4700uF output cap. On the mids, I had planned on 2200uF, and on the tweeters I thought 47uF might suffice. Crossover frequencies will be 220Hz and 3500Hz.

Anyone think that this will sound like total ****? I love how my array sounds - 9 super-cheap Pioneers from PE and 18 3/8" Onkyo tweeters driven by an LM3875 and an LM1875 with a pair of 24dB/octave active crossovers. I just wanted to go for a simpler circuit, and maybe a tad cheaper.. I figured it'd come out a lot cleaner without the extra parts.

Also, is this the correct way to do the crossover?

LPF->Sum with other channel for sub
HPF->
->LPF->Midrange
->HPF->Tweeter

Should a buffer go on each filter, or is permissible to leave them out when connecting them in chains like that?

Aside from my easily answerable questions, has anyone actually used the LM4752?
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Old 28th July 2005, 09:23 AM   #2
Wombat2 is offline Wombat2  Australia
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I'm about to ! I plan to use it as a tweeter amp in a triamp system. I have reduced the size of the application circuit from the data sheet - mainly by using pins instead of sockets. I decided on this chip because it has a single 24volt supply and I happened to have a regulated 24V PSU I picked up cheap. Just been notified my samples are on their way so I'll start the boards this weekend.

David L
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Old 3rd August 2005, 05:52 AM   #3
Wombat2 is offline Wombat2  Australia
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Dumb question - the tab and the centre ground pin are connected - would you insulate the the chip from the heatsink?

David L
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