[hpsdr] hermes aduio noise

[FRANCIS CARCIA]

Hi All,
This hit me going over the river and through the woods Wednesday night. Most of these audio amplifier chips need to be AC coupled to a speaker. The DC resistance of a speaker is usually quite low so the amplifier chip could be in hickup mode going in and out of current limit. You need to use at least 500uf in series with the speaker with positive side facing the amplifier. A larger value cap will provide better low frequency response. I didn't see any large caps on Hermes so it might be a good idea to put the cap inside the speaker enclosure.  Frank WA1GFZ
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