开云体育

I have a new (couple weeks old) v4 board that has trouble with Rx audio quality. Sounds distorted with very uneven frequency (no low frequencies). Speech barely intelligibly.
I saw other threads on distorted audio, and have tried these fixes:

1. Applied a 100 ohm resistor in series with the audio output to attenuate signal. Definitely dropped the output level, but the sound quality remained poor.
2. Did Raj's fix: lifted D15 and wired a 100-ohm preset inline, tried to adjust for less distortion. Perhaps some improvement, but not dramatic.

This evening I piped the audio into a spectrum analyzer (I'm tuned to an empty frequency on 40M, but same on all frequencies, both USB and LSB). The shelf above 3.5k is expected, but what happened to audio under 1.5k? Looks same regardless of the setting on the r value between D15-D16. I assume this is not expected...

Any ideas on what to try next?

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