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power cables - not in the signal path?

According to popular wisdom the AC power is not in the signal path and therefore a power cord, AC conditioner or similar should have zero audible effect.

In a don quixotesque attempt I'd like to turn this perception around: the AC is 100% in the signal path - more so that the actual low-level signal that gets amplified, and I think I found the simple words to clarify this.

The low-level signal is actually only modulating the high-voltage (high-intensity) signal produced by the transformer. Those electrons from the transformer are the actual electrons we "hear". The low-level signal is simply lost in translation. In a simple example, a 0.1V peak-to-peak sine signal gets amplified (say) 10x by a 10 V continuous (transformed) DC. The output is (say) a 1V sinusoid oscillating back and forth in time. If the 10V continuous is NOT actually exactly 10V (but is actually has noise) - then the noise will directly reappear "riding" on the 1V output.

Hence the need to keep the AC noise-free.

(Of course I purposefully neglected for simplicity the other effects (need for instantaneous delivery of power, etc..) for which I did not find a simple enough description (without reference to I/V curves and impedance / capacitance details, that is).

Does is make sense?

Thanks
C.
cbozdog
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almarg
9,670 posts
 
In a don quixotesque attempt I'd like to turn this perception around: the AC is 100% in the signal path - more so that the actual low-level signal that gets amplified, and I think I found the simple words to clarify this.

The low-level signal is actually only modulating the high-voltage (high-intensity) signal produced by the transformer. Those electrons from the transformer are the actual electrons we "hear". The low-level signal is simply lost in translation. In a simple example, a 0.1V peak-to-peak sine signal gets amplified (say) 10x by a 10 V continuous (transformed) DC. The output is (say) a 1V sinusoid oscillating back and forth in time. If the 10V continuous is NOT actually exactly 10V (but is actually has noise) - then the noise will directly reappear "riding" on the 1V output.
No, that is not correct. The main thing you are not realizing is that the circuit stages which provide amplification have a property known as Power Supply Rejection Ratio (PSRR), which (assuming reasonably competent design) results in the amount of noise appearing at the outputs of those stages being GREATLY less than the amount of noise which may be present on the DC power being supplied to them.

Also, of course, in the process of converting AC to DC the component's power supply itself will greatly reduce noise that is present on the incoming AC, as will filtering and "decoupling" capacitors that are normally provided at numerous locations elsewhere in the design.

IMO it is a misleading oversimplification to consider the AC power provided to a component as being in the signal path, while at the same time it would be incorrect to view AC power as not being able to affect the signal path.

Regards,
-- Al
czarivey
5,946 posts
 
C, R U trippin? Can you share info with substance abuser like I am on substance to use? It must be darn great!
zd542
5,339 posts
 
Would this be a good way to visualize it?

Think of a car as an audio system and the road represents your power/electricity. The car/audio system has a level of maximum performance it can achieve. But you can only get the best performance if you drive on a very good road. If you drive on a road that is in bad condition, you can't drive the car to its fullest potential. So even though the electricity going through the power cables in not part of the signal path, it can still effect it.
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