[hpsdr] TAPR Hermes - Noise on Audio Out

[Tom McDermott]

Hi Ron,
 
I have one PC that does this. A quick and easy check is to turn off VAC (Virtual
Audio Cable) function - a checkbox on the PSDR screen. Then hookup your computer
speaker to the headphone jack on Hermes instead of your computer.  When I did this,
the audio went from scratchy to clean. Running the DPC checks as suggested did not
indicate any issue with the problem computer.
 
-- Tom, N5EG
 


>________________________________
>From: Ron Nelson <ronelson99 at gmail.com>
>To: hpsdr at lists.openhpsdr.org 
>Sent: Thursday, November 22, 2012 11:37 PM
>Subject: Re: [hpsdr] TAPR Hermes - Noise on Audio Out
>
>***** High Performance Software Defined Radio Discussion List *****
>
>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
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