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Old 19th April 2008, 12:06 PM   #1
zhane is offline zhane  Singapore
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Default Need some help with DAC and LM386

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I've used a DAC0830 to connect with LM386 as shown in the schematic above.

I'm able to reproduce the voice I need correctly, but there is always this buzz that comes along with the sound.

It sounds like this :

Sound output from LM386

Can anyone advise me on what I can do to get rid of that buzz?
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Old 20th April 2008, 06:40 PM   #2
Minion is offline Minion  Canada
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The LM386 is not a very quiet IC...It is actually very noisy and probably isnt suitable for what you want to use it for....

They use the LM386 for small Battery powered amps and they are used quite a bit in Distortion pedals because they are so noisy...

I would select a better audio opamp.....


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Old 20th April 2008, 07:19 PM   #3
zhane is offline zhane  Singapore
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i dont have a choice of changing it
need to make it work the way it is
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Old 20th April 2008, 07:21 PM   #4
Minion is offline Minion  Canada
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Location: Cowican Bay , vancouver island
Quote:
Originally posted by zhane
i dont have a choice of changing it
need to make it work the way it is

Then you are Probably SOL.... you can"t make a noisy opamp and quiet one...also I can"t see the schematic to check if for any Problems so If you can re-post it maybe I can take a look...

Cheers
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Old 21st April 2008, 01:54 PM   #5
zhane is offline zhane  Singapore
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Click the image to open in full size.

this is the one
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Old 21st April 2008, 07:32 PM   #6
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I have no idea how big is the output ac voltage of your DAC, but I'm sure that you don't need 200x gain for the LM386, that you've set with the 10uF capacitor between pin 1 and 8.

Leaving pin 1 and 8 floating gives a gain of 20, I think that would be pretty enough for your application, so I suggest to simply remove the capacitor between pin 1 and 8. (or any gain can be set between 20 and 200, just have a look at the datasheet of LM386...)

One more thing: the capacitor between pin 7 and GND is VERY useful against noises, do not ever skip it.

Unnecessary gain can easily produce disturbing noise.
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Old 21st April 2008, 07:38 PM   #7
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And the DAC shouldn't be DC-coupled to the LM368, put a 10uF cap between pin 11 and the pot.
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