[hpsdr] TAPR Hermes - Noise on Audio Out

[Ron Nelson]

Thanks to all for comments and suggestions.

On a different desktop computer, Hermes works fine with no extraneous 
audio noise. I tried with both PowerSDR 2.2.3 (10/27/12) and cuSDR. 
Works great!

On my "problem" desktop PC the audio output noise continues to be 
completely reproducible. More tests:

I updated from PowerSDR 2.2.3 (10/07/12) to (10/27/12) - made no 
difference in the noise. So I am using the latest software now.

The noise is completely independent of the audio settings, volume, 
sample rate, sample size, etc. It is on both the headphone and speaker 
outputs. Everything points to oscillation of the audio output stage. The 
ADC and FPGA are working fine - the RF spectrum and signals are as 
expected. I can receive stations, but it is very annoying to listen with 
the constant  loud noise, and forget about listening to weak stations.

With PowerSDR in the "Off" state there is no audio output, as expected. 
With the ethernet cable disconnected the audio output also turns off, as 
expected.

The noise is there whether I use headphones or speakers.

I tried different ethernet cables (direct to PC) with no change.

Because I have such a good testbed for tracking down the problem ;->, I 
am willing to try some mods. Adding capacitance to the audio outputs or 
power for the D-A converter has been suggested. I may try this after a 
good nights sleep. Or I may try adding a different ethernet port to the 
PC to see if that makes a difference.

73
Ron
NR5ON

 1353656264.0