Author Topic: PreenFM Noise issue; whining, tone, high pitch  (Read 57 times)

served

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PreenFM Noise issue; whining, tone, high pitch
« on: July 23, 2018, 08:04:17 AM »
Hello,

Just writing for the community about the last discovery about The noise.

In short.

Reason:
The noise in the audio path is coming from the OLED screen inductor.
I will discuss the cause noise itself later.

Measuring:
This is a spectrometer screenshot. The conditions for dB measurements are relative. Signal has been run through a MIC preamp with full gain.
Condtions are exactly the same for all the measurements, so you can compare.

Observation1:
PreenFM 2 with Yellow OLED screen. This is what the peak looks like when the noise is present in the audio signal.
dB scale measurement is only for comparsion. Its peak is around 13650 Hz = 13,650 kHz


Test 1:
Aluminium shield between the OLED screen and main board. 0,75mm thickness, no ground.



Test 2:
Shielded SMD inductor instead of the original open inductor. Observe the shift in the frequency.


Test 3:
Shilded SMD inductor plus Aluminium shield.
« Last Edit: July 23, 2018, 08:29:12 PM by served »