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Old 30th July 2008, 10:47 PM   #1
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Default Laptop sound system?

I am exploring the possibilities of making a gainclone based around the LM1875 chip and a pair of full range miniature drivers for a laptop sound system. I already have a LM3875 system utilising Tannoy Mercury M1 speakers.

http://www.diyaudio.com/forums/showt...27#post1519127

I took the 3875 system away with me on a course recently, but found it too cumbersome to be lugging around. There was an issue with hum when using the laptop power supply, but it worked fine on the battery. Also, when the laptop went into hibernation, the S%^t hit the fan. The clone went overdrive and tried to cook the speakers. I nearly threw my coffee all over the place.

The system would have to be small and portable, although a 2 box system (PSU/AMP) would not be a problem. Some sort of protection from the laptop is also desirable. As I go away quite a lot (in shared accommodation), I don't need a particularly loud system (hence the LM1875 chip). For the same reason the speakers don't need to produce seismic bass. Just as long as they produce clear, detailed music, I will be more than happy.

Any ideas or experiences would be greatly appreciated.
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Old 31st July 2008, 02:19 AM   #2
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How many watts you want to pump out of a LM1875??
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Old 31st July 2008, 07:58 AM   #3
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Try TDA2030, 2040 or 2050.. good operation on 12-24 V..
Amplifer layout is small and won't load the laptop battery much..
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Old 31st July 2008, 11:00 AM   #4
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Quote:
Originally posted by kuldeepsingh
Try TDA2030, 2040 or 2050.. good operation on 12-24 V..
Amplifer layout is small and won't load the laptop battery much..

Thanks. I've had a look at the data sheet for the TDA2030. Too many components for my liking. I prefer the simplicity of the LM1875. I could always limit the gain.
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Old 31st July 2008, 03:04 PM   #5
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I got satisfying results from LM1876 for a "laptop sound system".

It is a stereo IC with about the same power per channel as the LM1875 at slightly better specs. Connected to a ridiculous power supply (2x9V 15VA transformer plus 4700F per rail) it makes music that starts to clip well above a normal background listening level, but well below loud listening as well. Until that point it sounds better than most people's home entertainment systems. I use it with an old Canton sat-/sub-system, which I think was specified as 82 or 83 dB/W/1m.

At my workdesk, where it is used now, it is more than loud enough, because the listening distance to the speakers is only 50 to 70cm. The volume potentiometer is usually very close to its counterclockwise limit. Few people, who hear the amp, believe that it only delivers about 5W per channel into those 8Ohm speakers.

Quote:
Originally posted by zebra100
Also, when the laptop went into hibernation, the S%^t hit the fan. The clone went overdrive and tried to cook the speakers.
I had the same problem with my old laptop. When I switched it off, the SPiKe protection system went wild. As my LM1876 is DC coupled I suspected DC coming from the laptops headphone output, but never verified it by adding Cin to see, if the noise went away. So I took care to always switch the amp off before the laptop, until the day, when I would try AC coupling. Of course that day would never come.
A few weeks ago I got a new laptop, and the effect was gone. So DC coupled it remains.

Nice, small and good sounding speakers for that purpose are CT227 (Aurasound NS3-193-8A with a reactance circuit against a hump in the mids), and CT237 (TangBand W4-1320 with a low-pass to tame the highs) from German Klang+Ton DIY magazine.
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