[joemg]

I'm currently using a M-Audio hiface 2 (technically a transport, not a DAC, but same theory) with a custom usb cable that gets power from a battery instead of the PC.  The battery is kind of a hassle, so it got me thinking... what if I just power it from the USB port on the receiver it's connected to.  My thinking is that there couldn't possibly be any loss in quality because it's the same power the receiver is using.  Are there any holes in this theory?

 

[joemg]

anyone?

 

[Andrew_WOT]

iFi Audio iUSB Power.

 

[joemg]

Quote:

iFi Audio iUSB Power.

I'm not sure that answers my question.
 
The question is if the USB device is powered from the receiver it is transmitting audio to, would that be the best possible scenario since any perceived gain from an external power supply would, in theory, be reduced once the audio makes it to the receiver?  in other words, the 'noise' could never be less than the 'noise' in the receiver's power, correct?

 

[A_Man_Eating_Duck]

Can you actually hear any noise through the USB power source(s)?

 

[PleasantSounds]

Quote:

I'm not sure that answers my question.
 
The question is if the USB device is powered from the receiver it is transmitting audio to, would that be the best possible scenario since any perceived gain from an external power supply would, in theory, be reduced once the audio makes it to the receiver?  in other words, the 'noise' could never be less than the 'noise' in the receiver's power, correct?

 
I doubt you would hear any difference, but theoretically speaking you need to consider also the following:
 

1. The actual noise from the power source is most likely further filtered in the DAC, which would reduce any potential differences. 
2. It's not the absolute level of noise that matters, but the signal to noise ratio. The signal output from the DAC chip may need to be amplified to get it to the line level required for output, i.e. DAC is likely to benefit from the cleaner power source more than the power amp. In other words, the noise added to the signal in the DAC is going to be amplified in the amp, therefore it may have higher impact on the output. Having said that, this is just a speculation as I'm not sure what signal levels are present on the M-audio's DAC chip.
3. The auxiliary power output implementations in receivers may not be the same as their internal power. Usually the power supply must provide at least two outputs: lower for the digital circuits/pre-amp etc., and higher for the power amp. They may have different filtering implemented and the aux power could be hooked to either of them or be a separate line.

 

[joemg]

Quote:

 
I doubt you would hear any difference, but theoretically speaking you need to consider also the following:
 

1. The actual noise from the power source is most likely further filtered in the DAC, which would reduce any potential differences. 
2. It's not the absolute level of noise that matters, but the signal to noise ratio. The signal output from the DAC chip may need to be amplified to get it to the line level required for output, i.e. DAC is likely to benefit from the cleaner power source more than the power amp. In other words, the noise added to the signal in the DAC is going to be amplified in the amp, therefore it may have higher impact on the output. Having said that, this is just a speculation as I'm not sure what signal levels are present on the M-audio's DAC chip.
3. The auxiliary power output implementations in receivers may not be the same as their internal power. Usually the power supply must provide at least two outputs: lower for the digital circuits/pre-amp etc., and higher for the power amp. They may have different filtering implemented and the aux power could be hooked to either of them or be a separate line.

 
Ahh, that makes sense...  Thank you for the detailed response!