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-   -   Dolby sorround 8.1 (LM4780) (http://www.diyaudio.com/forums/chip-amps/118417-dolby-sorround-8-1-lm4780.html)

David(ITA) 29th February 2008 12:43 PM

Dolby sorround 8.1 (LM4780)
 
Hi to all , I'm new here and i don't know very well english.
Ok now i'll tell you my problem about the costruction of a dolby sorround 8.1.I want create it whit a mpc509 (analogic multiplexer) for channel choosing, a tda3810 (this chip create spatial stereo) for the rear channel , and lateral channel , a lm324( low power op-amp) for preamplifing all but before of the pre amplifier i want put some cross over that for the high cut (300hz to 20khz) and low cut (20hz to 300hz), 8 high cut for all the channel and one low cut for the sub channel. I want to use four LM4780 for the eight channel but i don't know what use for the sub. Second you a bridged lm4780 can be good ? How can be the dissipation of all this component second you ?
Excuse me if I've wrong , but i didn't know where wirite this thing

Dxvideo 29th February 2008 01:04 PM

Hi David,

I think LM324 is not a good idea for filtering and preamp section. You must use a better opamp for this position; like OPA4134.
And for the sub power amp, if you will use 4ohm subwoofer then you must use LM4780 in parallel, and if you will use a 8ohm subwoofer then bridge configuration is better. In any case you will have double power of one channel LM4780.
About the power dissipation; I think you will need huge heatsinks. Because 9 channel LM4780 creates a lot of heat (at least 30W per channel!)

MartyM 2nd March 2008 08:09 PM

Hello! I can answer a little bit about multi-channel application.

I doing something very similiar to you, except for the car.

I have a 5.1 D.Digital/DTS decoder in my car, and wanted a TRUE 5.1 channel amplifier, which is not available on the car audio market.

So what I did was I made 9 identical LM3886 modules to be used like this:

1. 5 identical PA100 modules for main channels: LF, RF, center, RR,LR
2. Two spare front channels, for midbass (LF#2, RF#2)
3. Two remaining PA100s used together form a BPA200 bridged for subwoofer channel

Two PA100s were enough remaining for making the subwoofer channel by slightly modifying one module into the inverting mode. Then together they form the BPA200.

Basically only trivially different from the LM4780 (same general design, etc.)

That's pretty easy, except having difficulty with the servo circuit. But that is optional.

But YES, you better make sure to use very large heatsinks.

Good luck!

David(ITA) 3rd March 2008 06:40 PM

I'm very happy from your advertise :D :D


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