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Old 4th May 2010, 05:35 PM   #1
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Default low power high quality chip amp needed

hello
i want to build a 3-way active pc speaker and I need simple, low power(
about 10w) and high quality chip amps for amplifying tweeters and mid-ranges.
thank you


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Old 4th May 2010, 06:15 PM   #2
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Depends what is available where you shop.

Check out the LM1876 for mid-range and tweeter. It has two channels, so you only need one for each speaker and it is easy to find.
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Old 4th May 2010, 07:35 PM   #3
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10W into four or eight ohms? An option to consider at the lower end of that range is using an op amp and STD03s; same basic idea as the LME49811+STD03 builds on this forum, just with lower rails and reduced output swing. More complicated than a LM1875/LM3886/LM4780, but also higher performance with a good op amp (LME49710 or LME49990 are good starting points). And still much simpler than a discrete amp.
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Old 5th May 2010, 04:49 AM   #4
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Quote:
Originally Posted by hamedfazelm View Post
hello
i want to build a 3-way active pc speaker and I need simple, low power(
about 10w) and high quality chip amps for amplifying tweeters and mid-ranges.
thank you


I suggest LME49811 with Class A output stage. Our ears are most sensitive to these freq. With Class A, you don't have high-order crossover and switching distortions. Low power Class A is not difficult/expensive to build.
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Old 5th May 2010, 05:25 AM   #5
preiter is offline preiter  United States
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Wrong forum, I know, but I would look into Class-T. High quality, cheap and you can get commercial 12v power supplies everywhere.
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Old 5th May 2010, 12:04 PM   #6
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Originally Posted by panson_hk View Post
I suggest LME49811 with Class A output stage.
Why not class A with an op amp? Or AB? The 49811 measurements I've seen hold 0.01% THD in the transition from A to B, so I'd expect the subjective differences between class A and AB 49811 designs to be small to negligible. Assuming appropriate supplies, anyway. The 49710 and 49990 have higher Avol and GBP than the 49811 and are unity gain stable and lower offset. So they offer a better system gain budget, greater excess loop gain (particularly in the highs), and reduced need for a DC servo or blocking caps.

It occurs to me an op amp plus STD03s (or STD01s) without a servo is arguably no more complex than a servoed LM3886 or similar.

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Originally Posted by preiter View Post
Wrong forum, I know, but I would look into Class-T. High quality, cheap and you can get commercial 12v power supplies everywhere.
For class D I'd look to the ADAU1592 first.
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Old 6th May 2010, 02:17 AM   #7
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Originally Posted by twest820 View Post
Why not class A with an op amp? Or AB? The 49811 measurements I've seen hold 0.01% THD in the transition from A to B, so I'd expect the subjective differences between class A and AB 49811 designs to be small to negligible. Assuming appropriate supplies, anyway. The 49710 and 49990 have higher Avol and GBP than the 49811 and are unity gain stable and lower offset. So they offer a better system gain budget, greater excess loop gain (particularly in the highs), and reduced need for a DC servo or blocking caps.
Interesting combination for low power applications.

A test of 49810 with Class A output stage shows THD < 0.005 % for 10 W into 8 Ohm. The harmonic structure is more important than the pure THD number.
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File Type: jpg THD vs freq 10W 8R.JPG (90.1 KB, 396 views)
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Old 6th May 2010, 02:38 AM   #8
asbjbo is offline asbjbo  Norway
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What is the noise level of the LME49810/Class A combination?

I'm looking for quiet amplifiers for a high efficiency, multiway active loudspeaker project. Class D and LM4780 chipamps will typically generate 30-40 uV of noise when idling, and that is enough to be audible on a high efficency loudspeaker. Perhaps LME49810/ThermalTrak biased for class A up to 1 W, say, does better?
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Old 6th May 2010, 02:38 AM   #9
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Agree on harmonic structure. Though at O(0.001%) THD I'm unsure how much details matter since everything is really small.

10W is pretty loud, particularly for triamped nearfield listening to computer speakers---assuming 90dB efficient drivers that'd be roughly 109dB at the listening position. 60dB is probably more typical; that's roughly the SPL of an animated conversation. Power wise it's in the vicinity of 500uW per side, with around 225uW into the mid and bass and 50uW into the tweeter. The numbers'll obviously shift around some based on the speaker design and driver choice, but the power range of primary interest is likely the 10uW to 10mW space. That's usually comfortably within the class A range of a class AB.

Does pure class A offer benefit at such powers? I've seen 3886 and 49811 class AB measurements which go that low, but were done on equipment with a THD floor of 0.003% and hence could only report the 49811+STD03 was below the noise floor. In comparison, the 3886 was around 0.6%. Not aware of any data for a 49810.
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Old 6th May 2010, 02:52 AM   #10
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Originally Posted by asbjbo View Post
What is the noise level of the LME49810/Class A combination?
You'll find an output noise spec in the 49810 datasheet if you look. Of themselves, the 49810/49811 are about 8dB noisier than the 3886/4780 whereas the 49710/49990 are 30 or 40dB quieter when operated at unity gain. Actually hitting the op amps' noise floor will take some careful board layout.

I'm unsure of the output devices' effects, though I'd expect the usual sum of squares.

Last edited by twest820; 6th May 2010 at 02:59 AM.
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