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Old 1st March 2004, 06:08 AM   #1
dzent56 is offline dzent56  Indonesia
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Default Need help about 2.1 aranggement

Hi, I am about to make my first gainclone. I planned to use 2.1 aranggement for my PC speaker. I will use 3 LM1875 based amplifier, 2 for satelitte and 1 for subwoofer. But I had a sort of problem since I was new in DIY audio. How could I mix / get low frequency signal from normal stereo signal (left and right) to feed my subwoofer amplifier. I saw it in many PC speaker that commercially available, but had no idea how to make it. Anyone can help me? ,Please...............Currently, I had built the first 2 channel, and it works! but there was an annoying "thump" sound when I turn on/off the power, does it normal?. Is there any easy solution to fix this problem? ........for note: I use standard application for LM1875 from ESP home page.
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Old 1st March 2004, 07:08 AM   #2
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Default 2.1 System

First thing u need to do in making a 2.1 system is that u have to make a summing amplifier to add inputs from satellites, then a low pass filter preferable 3rd order and then a power amplifier.
For the thumping issue I have never used 1875 so don't know if its a problem with the IC itself..
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Old 1st March 2004, 08:18 AM   #3
Nuuk is offline Nuuk  United Kingdom
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Quote:
Currently, I had built the first 2 channel, and it works! but there was an annoying "thump" sound when I turn on/off the power, does it normal?.
We will need to see your complete circuit diagram and list of components to help you with that problem.
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Old 1st March 2004, 08:27 AM   #4
sreten is offline sreten  United Kingdom
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Basically the cheap computer way of doing things :

You use a single ended supply.

You arrange one channel to be inverting.

You use the same virtual ground for both channels.

You reverse the connections on one of the satellites.

The coupling capacitor (a polar electrolytic, not a
more expensive non-polar) is also the crossover
capacitor for the satellites.

As you've used the same virtual ground the amplifiers
DC outputs should be very similar and due to inverting
one channel for mono signals they are effectively bridged.

(You can force this by monoing the input a low frequencies)

So the subwoofer is wired across the outputs before the
satellite coupling capacitors with an inductor in series
as its crossover.

By using different impedance speakers you can control
relative powers to a degree, but I'd suggest 4 ohm
satellites and an 8 ohm subwoofer.

sreten.
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Old 1st March 2004, 12:17 PM   #5
Morse is offline Morse  United States
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Hi Dzent56;

On the turnoff thump issue, have you used bounce caps on the power switch? I had a significant turnoff "pop" or "thump" with my TDA2030A when first built, but bounce caps fixed it (as they've done on other electronics projects in the past - only reason I didn't use 'em up front was that I didn't want to waste a pair of .01uF 3kV rated ceramic discs if I didn't need to). If you install bounce caps, it's ESSENTIAL that they be able to handle the huge voltage spike, and that means at least 2-3kV rated ceramic discs, at minimum.

On the subwoofer out, another way of doing it is at http://sound.westhost.com/project18.htm in Figure 3. He's also got a rear channel and a centre channel, but you needn't use them. I've not built this circuit, but it looks interesting, and I'm considering it for a 2.1 microsystem myself. If you build it, please post the results!

Good luck on whatever you build and all the best!
Morse
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Old 1st March 2004, 02:10 PM   #6
dzent56 is offline dzent56  Indonesia
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Quote:
We will need to see your complete circuit diagram and list of components to help you with that problem.
Well, I don't think that I have any permission to display the schematic in here, I don't want to violate any person's copyright. But, if you want to do some favor for me you can look the schematic at this link http://sound.westhost.com/project72.htm .
I dont use a pcb, so I wired it point to point using a board that have many holes on it (I dont know what to call it). All the resistors are 1% metal film, bypass caps are ceramics disk, 220nF output cap is Mylar, then I use polarized 2.2uF caps for input coupling (I dont have nonpolarized caps at that time so I just used the elco, does this matter?) because the IC is difficult to mount on the board, I use a wire to connect each pin to the board, altough I know that will lenghten the feedback path. I planned to build my own pcb, but I had to sure that everything is ok, in my country making pcb is quietly expensive, especially for student like me. Anyway, thanks for all your help.
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