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Fish32

fft noise and thd

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Hi,

I'm trying to make audio noise, spectrum & thd measurements on opamp circuits but the noise and distortion with the Analog Discovery 2 is so high (see attached pict) even without anything connected so it's not possible. Am I missing something obvious here ? What's all that noise below 6kHz ?56c5c9089905e_Screenshot2016-02-18at13.0

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Hi,

To have better horizontal resolution, adjust the Frequency Range to the interested domain or set it to Auto.

To have better vertical resolution, lower the Magnitude Top level (<= 3dBV) or adjust the Range for scope inputs, under Channel options.

i5.png

Edited by attila

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Hi Attila,

 

thank you for your quick reply.

I've adjusted the settings and it already looks much better.

The THD is still very high with my Analog Discovery 2 (around 0-10dB) , not -77dB as on your screenshot .

Will using the BNC adapter reduce noise & distortion?

 

thanks again

 

 

Screen shot 2016-02-18 at 19.34.04.png

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I use to twist the Scope input wire pairs (+/-), connect the negative input to reference (or ground) near the positive test point, and twist AWG with GND. These help in reducing the noise.

With the BNC Adapter and probe you can obtain better noise rejection, but loose the differential scope input. The BNC is not differential, the negative input is shorted to GND on the adapter.

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