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Chip Amps Amplifiers based on integrated circuits

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Old 23rd January 2004, 01:06 PM   #11
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Join Date: Mar 2003
Location: Lisbon, Portugal
Quote:
Originally posted by soundNERD
Thanks everybody!
carlosfm, a stupid question: where does the dual pot connect? I see all standard resistors in the schematics. Sorry for how stupid this question is
The dual pot is in place of the input resistors.
Don't you see two resistors bebore the NI input?
If you make that variable (with a pot), you have a variable filter.

Quote:
Originally posted by soundNERD
Also, just wondering, how much power can an OPA549 deliver? The datasheet didn't say. [/B]
I have no idea.
Maby someone can help with the maths.

BTW the OPA549s sounds so good (without the filter, that is) that it seams like a crime to use them on a sub.
When I connect the filter, I loose the midband and treble.
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Old 23rd January 2004, 01:38 PM   #12
macboy is offline macboy  Canada
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Location: Ottawa, Canada
Quote:
Also, just wondering, how much power can an OPA549 deliver? The datasheet didn't say
Well, since this isn't specifically an audio amplifier, I am not surprised that power output ratings for speaker loads (4 ohm, 8 ohm) are not given in the datasheet. However, if you look at the Total Harmonic Distortion graph, you will see several sets of lines, for different output power levels, and a note that the load is 4 ohms. One of the lines is for 75 W output. Note how the distortion rises sharply with frequency, even at low power output levels.
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Old 23rd January 2004, 02:35 PM   #13
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That's normal, isn't it?
Check the LM3875 datasheet and see the graph THD+N vs Frequency.
At 40w, 8 ohms.
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Old 23rd January 2004, 04:38 PM   #14
macboy is offline macboy  Canada
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Quote:
That's normal, isn't it?
Check the LM3875 datasheet and see the graph THD+N vs Frequency.
Actually, it is quite normal to see and increase in THD with frequency.

But check out the 3886. It's THD+N vs. Frequency curve is plotted with power out = 60 W into 4 ohms. At 20 kHz, the number is about 0.025%. For the 3875, with 40 W into 8 ohms, it is about 0.07%. And with the OPA549, at 75 W (or at 10 W) into 4 ohms it is about 0.2%. So what concerns me isn't that the THD increases with frequency, but how much it increases. The distortion in the 3886 increases by a factor of 10 from low frequencies to high frequencies. The distortion in the OPA549 increases by a factor of 100 from low frequencies to high frequencies.
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Old 24th January 2004, 01:37 AM   #15
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Location: Illinois
Whats the highest power chip TI makes?

I want to use this for a sub, so high-freq. distortion isn't an issue.

Also, do they have any high power opamps that can be mounted to a standard heatsink?
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