Power Conditioners and Cords

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#41
I think that you miss hearing the background noise that the ferrites remove.
forum member 'DF96' (RIP) has written about noise as detail.

What is wrong with that is that perceptions of "detail" can be fooled by the presence of extra noise and interference. Hence you may be choosing the amp with inferior interference rejection. This issue is a reason why some DIY cables (with appallingly bad design or construction, so admitting lots of RFI) are perceived to give more 'detail'.
 
#44
RFI only causes a DC offset if the RFI is constant. They normally test with a pulsed sine wave RF source, which can be seen as a pulsed DC offset. If the RFI is changing over time, then so will the offset. Basically the RFI can demodulated by semiconductor junctions which can also then intermodulate an audio signal with demodulated RFI. In that case we may expect to find 'signal correlated noise,' which tends to be more audible than uncorrelated noise. On an FFT correlated noise may be seen as a shift of the baseline FFT noise floor based on the presence or absence of an audio test tone, and or as a change in the noise skirts around the base of the audio signal spectral peak under different experimental test conditions (say, for example, with the presence or absence of an AC power line filter). However it may take a very high resolution FFT to show the noise skirts clearly.
 
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#45
Rick Miller said:
...what measurement would show what you want to see?
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If you just want to see if there is noise on the AC line, an RF spectrum analyzer, safely and carefully connected to show AC line noise, may be useful to try. Turning on or off something like a vacuum cleaner connected to the same outlet as the audio system should show pretty easily measured noise on the line (just to check that the test setup is basically working, of course, not as an expected condition while listening to music).
 
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#46
Markw4 said:
RFI only causes a DC offset if the RFI is constant. They normally test with a pulsed sine wave RF source, which can be seen as a pulsed DC offset. If the RFI is changing over time, then so will the offset. Basically the RFI can demodulated by semiconductor junctions which can also then intermodulate an audio signal with demodulated RFI. In that case we may expect to find 'signal correlated noise,' which tends to be more audible than uncorrelated noise. On an FFT correlated noise may be seen as a shift of the baseline FFT noise floor based on the presence or absence of an audio test tone, and or as a change in the noise skirts around the base of the audio signal spectral peak under different experimental test conditions (say, for example, with the presence or absence of an AC power line filter). However it may take a very high resolution FFT to show the noise skirts clearly.
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I think that the ADI ap-note referred to an anecdote in which a ham radio handi-talkie was interfering with some measurement circuit. I've also heard that you can modulate those clear 1N4148's with fluorescent lights.

In any event, good bypassing and layout technique can obviate...
 
#48
jackinnj said:
...good bypassing and layout technique can obviate...
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Don't know that I would use quite such absolute language. Whole books have been written on electromagnetic compatibility. Seems maybe more accurate to say something like, 'various methods can be used to attenuate RFI effects to negligible levels for a given application,' or something to that effect 🙂
 
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#50
The terms RFI and EMI are often used interchangeably.

One explanation: https://resources.pcb.cadence.com/blog/2022-the-basics-of-emi-and-rfi

Many similar explanations: https://www.google.com/search?q=RFI...i30j0i390l2.8984j0j1&sourceid=chrome&ie=UTF-8

For some information on DC offset, pleast see: https://www.ti.com/lit/an/snoa497b/snoa497b.pdf ...It may be noted that the specification is about EMI, however Figure 1 in the document is entitled: 'Offset Voltage Variation Due to a Detected RF Signal'
 
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#55
I see what you mean. Thing is that AC lines sometimes act as antennas and or conduits for RFI. A DC offset in an amplifier as described in the TI app note can occur if that RFI makes ingress though the device AC power inlet, then passes through the power supply and or bypasses it through parasitic coupling. Its not just theoretical, its been known to happen.
 
#57
ceulrich said:
if they did not do something positive, I don’t think the market would keep growing,
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One would like to think that, yes. Question is, positive what?

Even answering, "positive utility" is not clear enough because, utility toward what?

"Positive utility toward making music" is simply not the entirety of what drives the consumer of audio appliances. DIY, "positive utility toward making music" can suffice, and is a full plate!

But the consumer world and the DIY world are two different universes with a shared atmosphere. Or something. Because in the consumer market, evidence shows people will find "positive utility" in anything the traffic will allow. The audio business does not watch music. The audio business watches the people who like music. And it sells things to them. It will sell them a brand of cable, called "This is no hype cable!" and then gradually introduce tiers of "This is no hype cable!" and "signature editions" and...

So, you know. The value of an audio good depends on the market one is considering. The consumer market and the DIY market are two distinct entities. Yet we breathe the same atmosphere. Or something.
 
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