Background...
Highly modified Xonar STX with external, DC regulated PSU.
RCA out to newly installed Granite Aspen tube preamp
RCA from there to modified and restored Dynaco MKIII mono amps.
Amps are ungrounded and on separate outlet (though probably the same circuit)
Aspen is grounded and connected to powerbar with PC, router, modem, TV
Since installing the pre, the amps are amplifying mouse movements, video changes and frequency switching of the vid card and/or CPU.
Of course, output to the pre is at full volume line level (to not introduce digital volume control)
Oddly, connecting the pc directly to the power amps (even at full line volume) has absolutely no noise at all except for the usual, low hiss.... It's only with the Aspen in the loop.
I careful routed all wiring, separated line level from power cables, twisted any AC power lines, insured all the PC cards are grounded to the chassis.
PSU and transformer for sound card PSU are isolated inside a Hammond chassis with the mainboard on top. Vid card and STX as far apart physically as possible.
Vid card runs HDMI 2.0 to tv on separate audio channel.
Wiggling the HDMI cable at the vid card causes some noise to also go thru amps....?
Any help would be appreciated!
Highly modified Xonar STX with external, DC regulated PSU.
RCA out to newly installed Granite Aspen tube preamp
RCA from there to modified and restored Dynaco MKIII mono amps.
Amps are ungrounded and on separate outlet (though probably the same circuit)
Aspen is grounded and connected to powerbar with PC, router, modem, TV
Since installing the pre, the amps are amplifying mouse movements, video changes and frequency switching of the vid card and/or CPU.
Of course, output to the pre is at full volume line level (to not introduce digital volume control)
Oddly, connecting the pc directly to the power amps (even at full line volume) has absolutely no noise at all except for the usual, low hiss.... It's only with the Aspen in the loop.
I careful routed all wiring, separated line level from power cables, twisted any AC power lines, insured all the PC cards are grounded to the chassis.
PSU and transformer for sound card PSU are isolated inside a Hammond chassis with the mainboard on top. Vid card and STX as far apart physically as possible.
Vid card runs HDMI 2.0 to tv on separate audio channel.
Wiggling the HDMI cable at the vid card causes some noise to also go thru amps....?
Any help would be appreciated!
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You have a ground loop between your pc and preamp.. you can transformer couple the connection between them or you can experiment with how you run power and line cables for your pc and preamp to see if you can reduce noise (minimise the loop area between power cables and the line cable between pc and preamp)
I've read about transformer use to remove a direct electrical connection between components.
Do you mean in the signal path? The RCA's....?
The return wire of your soundcard output (the shield ring of the output cinches, "output ground") is connected to your PCI slot ground trace. At that point there is a different potential from the PSU ground point where PE wire is connected. The difference contains all the huge return currents which run somewhere along the trace to the PSU ground point. A mouse move -> CPU wakeup + work -> GPU work -> current spike. Key pressed -> CPU wakeup + work -> GPU work -> current spike. Even letter appearing in linux terminal -> GPU work -> current spike (personal experience).
Normally this difference makes no problem since the soundcard live wire signal is derived from its ground potential - thus the output signal (i.e. live wire minus ground wire) contains only the clean signal.
However, if you hook the soundcard "ground" wire to your pre-amp which has its input "ground" wired to PE, the soundcard "ground" wire is connected to the PC PSU ground by two paths - one is the path on motherboard with the currents which generate the noise voltage potential, another the shield wire of your audio cable -> preamp PE wire -> PC PE wire -> PSU ground point. And the shield "ground" wire of your audio cable carries not only the return current for your audio signal, but also part of the noise currents generated by circuitry on your motherboard, generating small but audible noise voltage. And that is why you can hear mouse moving, hard drive seeking, changes on screen etc.
The solution is to break this loop:
* isolation audio transformer
* using only insulated devices without PE wire
* using balanced line connection where the output ground serves only as cable shield and does not carry the return audio signal.
Normally this difference makes no problem since the soundcard live wire signal is derived from its ground potential - thus the output signal (i.e. live wire minus ground wire) contains only the clean signal.
However, if you hook the soundcard "ground" wire to your pre-amp which has its input "ground" wired to PE, the soundcard "ground" wire is connected to the PC PSU ground by two paths - one is the path on motherboard with the currents which generate the noise voltage potential, another the shield wire of your audio cable -> preamp PE wire -> PC PE wire -> PSU ground point. And the shield "ground" wire of your audio cable carries not only the return current for your audio signal, but also part of the noise currents generated by circuitry on your motherboard, generating small but audible noise voltage. And that is why you can hear mouse moving, hard drive seeking, changes on screen etc.
The solution is to break this loop:
* isolation audio transformer
* using only insulated devices without PE wire
* using balanced line connection where the output ground serves only as cable shield and does not carry the return audio signal.
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The motherboard is connected to the PSU by many wires, each has a connector contact with varying level of resitance - perhaps the new PSU connectors changed the distribution of ground currents on the motherboard. Or different load capability - new PSU could generate larger current spikes -> more noise, etc. Loads of possible causes, likely in combination.
Great solution
Protective Earth; mains earth
What Phofman said, but you could try it shortly for a test. Also, the problem may be just too much gain; sound card full output to a sensitive preamp to amp.
Unfortunately that would not break the ground loop between your PC and the preamp.
How is it that my power amps were designed without an "earth" wire and work safely? There is over 600v running around in there!
There is huge gain in my signal path. I have 30v running to the soundcard opamps and I run it with sound "disabled" (max output) to eliminate digital volume control interfering with the stream. The Aspen is pretty potent as well... It only needs the volume dial turned just off min to get decent volume output.
If a device is designed to work this way then no problem. But if it comes with three wires mains cable, we should not violate this. Assuming your PC is connected to PE then you can do the above mentioned test to check if the problem is a ground loop.
[/QUOTE]There is huge gain in my signal path. I have 30v running to the soundcard opamps and I run it with sound "disabled" (max output) to eliminate digital volume control interfering with the stream. The Aspen is pretty potent as well... It only needs the volume dial turned just off min to get decent volume output.[/QUOTE]
Personally I would focus on this.
Honestly, I am surprised too
OK, you are running soundcard output at 100% to avoid digital volume control. That means the signal/noise ratio on your PC-preamp link is at maximum (the PC-generated noise is constant regardless of audio signal level). For that you have to attenuate the signal a lot in your pre-amp - but that is already behind the noisy line.
IMO when you lower the signal on the line with the soundcard volume control (and reduce the pre-amp attenuation accordingly), the noise will only get worse as it will be less attenuated by the pre-amp volume control...
I have a ST essence also modified. Among other things I've killed the opamp output stage and and connected the dac chip directly to a tube preamp via I/V resistors Those resistors set the output level of the sound card. The bigger the resistors the higher the signal. Preamp's huge gain was fine with 2 ohms - that is around 7,8mV peak. Moving to 56 ohm, the system became so nervus that in my soundstage I could have an holographic image of the chip's internal structure!
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