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Chip Amps Amplifiers based on integrated circuits

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Old 30th September 2012, 11:43 AM   #11
Kitax is offline Kitax  Latvia
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well if i want to know how big rezistor should i put there for the diodes to get their 2v, but now that i think of it, a good LED would be with rezistance very close to 0 as am i right?
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Old 30th September 2012, 12:03 PM   #12
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The LEDs will get their voltage as long as Vf is met or exceeded. No more and no less (in practical terms). If you are speaking of LED dynamic resistance still, it isn't a concern in anything but the most unusual of circuits, which this isn't. And the series resistor isn't overly critical; the 39 ohms suggested earlier seems like a good starting point. Or start with a larger value, say 100 ohms, and solder another resistor(s) in parallel if you need brighter output.
I'm not sure what units "0" refers to in your post.
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Old 30th September 2012, 01:40 PM   #13
Kitax is offline Kitax  Latvia
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well i'll just get an adjustable potentiometer, so i can adjust it, and let it sit inside the case...

ohms
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Old 3rd October 2012, 02:17 PM   #14
Kitax is offline Kitax  Latvia
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how should i make a low frequency filter, so the lights react more to the bass... i used RC filter, but it wasnt very effective, and i almost couldent feel the difference (just put a rezistor right after the diodes and the capacitor paralel, between the ground and output)
matbe i should modify the schematic to change the amplified frequencies, but i dont know how to...
(i used the datasheet schematic called "Amplifier with Gain = 200") i had it laying around
i think that the cutoff frequency should be around 50hz, but it depends on how good the filter is...
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Old 3rd October 2012, 03:25 PM   #15
johnr66 is offline johnr66  United States
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Sounds like your using the LM386. You need to filter on the input side. Use the RC impedance formula to find the pole frequency of 50Hz. If your using the output coupling cap, the one on the data sheet (220uf I think they used) is too small. Increase value to 1000uf if your driving power LEDs.
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Old 3rd October 2012, 07:55 PM   #16
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Quote:
how should i make a low frequency filter, so the lights react more to the bass...
Lower the gain (try 20x). And use the bass boost circuit from the datasheet.
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Old 4th October 2012, 12:57 PM   #17
Kitax is offline Kitax  Latvia
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damm was hoping, that it wouldent come to unsodering it, but i guess i have got to do it :S
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Old 4th October 2012, 01:36 PM   #18
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Check out the circuit in the datasheet... there's not much that needs to be changed. Remove one part and add two.
At 200x gain, virtually any input signal will light the LED. And the bass boost gives several dB more gain at <1kHz than at >1kHz.
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Old 4th October 2012, 06:16 PM   #19
Kitax is offline Kitax  Latvia
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actually i already have 200x gain, and i dont know why, but i dont feel the effects of bass boost...
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