[sdiy] High pitched noise on codec problem

julian schmidt elfenjunge at gmx.net
Thu Dec 5 21:22:18 CET 2013

> On 12/05/2013 11:59 AM, julian schmidt wrote:
>> Am 05.12.2013 19:12, schrieb Eric Brombaugh:
>>> Also - it's probably not a good idea to ground the unused input - it
>>> expects to be biased at ~AVDD/2, so grounding looks like a fullscale
>>> negative input which might do odd things to the input circuits.
>> on a 2nd thought... shouldn't any DC voltage be blocked by the cap after
>> the opamp anyways?
> So when you talk about "unused input" on your codec, it's actually 
> still driven by the op-amp, and when you talk about grounding the 
> input, you're not grounding the codec input but rather the op-amp input.

> I'd take a closer look at what your op-amp circuit is doing when you 
> touch it.
I could not measure any difference in the opamp circuit using my scope.

However i'm a little step further.
I noticed when I turn off the ADC highpass of the codec the noise is gone.

So I'm off reading the datasheet now to find out more about the 
highpass. Never bothered before to read the details about it.

Thanks for the help so far,

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