29421Re: [softrock40] Re: V9 output to audio card?
- Jan 2, 2009
----- Original Message -----
From: "Ken" >
> By "mains frequecy" you mean the 60 (or 50) cycles of the power line?
Yes, I thought I was talking the wrong language! Over here we often call the
50Hz main power supply line "the mains"
> A "lowish" value (such as in the pF range?)
That depends on the frequency and the line impedance. 10nF is a small value
at 50/60Hz so offers a considerably higher impedance than the direct
connection via the audio cable. Therefore little LF current flows through
> while allowing the "spiky" USB signal to pass....
> Is there any signals as such on the ground wire of the USB connection?
The spiky USB signal has to return to ground, so yes, they are there. If it
is a good low-resistance ground connection they will not be noticed.
> AND does the ground wire not need to be a DC ground that would be
> blocked by a capacitor?
The DC ground is connected via the audio ground.
> are you suggesting putting this "lowish" value capacitor on all the
> USB wires to isolate them to prevent any ground loops?
If there is a good ground return to the USB by way of the audio cable then
this capacitor may not be needed. I leave the USB ground disconnected to
avoid a ground loop at low frequencies. The 10nF capacitor just gives the
spiky signal an alternative route.
Again I stress that this is just the way I have done it. It seems that to
get the best results it may be necessary for people to experiment until they
are satisfied, their conclusions may differ from mine .
73 Alan G4ZFQ
- << Previous post in topic Next post in topic >>