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Power Cords

Sal1950

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Wow... That's 18 months ago... It's worse now...
Ha ha ha.
I see the dusting brush sitting right there but don't look like it's been used in a bit. :p
 

Sal1950

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RayDunzl

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I see the dusting brush sitting right there

I was looking for that... thanks!

Is the blue florescent tube lite for special effects?

Mood, yes.

Home Depot colored CFLs, about $4 each. Red is too dim, blue is pretty bright in a near-ultraviolet way. Red, yellow, and blue make a nice sunrise feel. So, being a contrarian, I have blue light at night, when, theoretically, I shouldn't.

"Where the stumblers gonna go
To watch the lights turn blue?"
- FZ
 
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tomelex

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So, looking at current used in the load, if you have 100W into 8 ohms about 3.5A, and into 4 ohm about 5A. So, if you are listening at 1W and you have a 10X peak, you are up to depending on impedance somewhere between 3.5 and 5 Amps.
 

fas42

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Maybe someone here has the tools and could simulate a simple power cord/transformer/rectifier/capacitor/load just to put some numbers on what 'really' goes on.
I did that very thing some years ago, but of course the power cord can't be simulated in the normal sense - or more accurately, the standard electrical properties of such are insignificant. But otherwise, conventional power supplies are a bit of a mess - that is, they are not robust: they generate very high frequency noise internally, which could couple to circuitry; and, the output level is heavily modulated by everything - the instantaneous draw by the load, the quality of the mains, the parasitics of all the power supply parts, which alter as the temperature of the supply pasts varies - it's a rats' nest! The beloved graphics in the textbooks, of how the smoothing capacitors make all that unpleasantness go away is miles from reality - if one goes to the trouble of modelling real word power supplies, and seeing what happens ...

Which means, that if one does just about anything to alter how the power supply is fed, or its environment looks, that the sound quality may change.
 

amirm

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I did that very thing some years ago, but of course the power cord can't be simulated in the normal sense - or more accurately, the standard electrical properties of such are insignificant. But otherwise, conventional power supplies are a bit of a mess - that is, they are not robust: they generate very high frequency noise internally, which could couple to circuitry; and, the output level is heavily modulated by everything - the instantaneous draw by the load, the quality of the mains, the parasitics of all the power supply parts, which alter as the temperature of the supply pasts varies - it's a rats' nest! The beloved graphics in the textbooks, of how the smoothing capacitors make all that unpleasantness go away is miles from reality - if one goes to the trouble of modelling real word power supplies, and seeing what happens ...

Which means, that if one does just about anything to alter how the power supply is fed, or its environment looks, that the sound quality may change.
Frank, from now on such statements need to be accompanied with measurements, references and/or formal listening tests. Otherwise I will be deleting them.

This forum is setup for learning and proper presentation of facts and data about audio. There are other places for speculation and opinions.
 

DonH56

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So, looking at current used in the load, if you have 100W into 8 ohms about 3.5A, and into 4 ohm about 5A. So, if you are listening at 1W and you have a 10X peak, you are up to depending on impedance somewhere between 3.5 and 5 Amps.

I don't get what you mean by "up to depending on impedance"?

Note peak currents from the line, which can be rather large and rather fast, depend heavily upon the power supply as well as the amplifier's design, signal, and the load. I did run some simulations a while back that I believe are posted over on WBF. That said, I have not measured them recently, but may try to grab one of our current probes and a DSO from work sometime to check it out.

Finally, a power cord can have some influence on the sound by filtering noise right at the point of service and of course supplying additional current if the stock cord is too small (unlikely IME). But those cases smack to me of poor component design...
 

amirm

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Sorry, are you saying that that if one models the parts of a real world supply using a Spice program, and it shows the behaviour of that circuit is not ideal, as is usually assumed - that such is not a valid "data point"?
Show the spice model and graphs. That would be welcome. Words saying this and that is not.
 

DonH56

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OK, but I'll have to dig them up. Or I can delete my post until I have proof, no worries.

Oops, found the paper, see attached.
 

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amirm

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OK, but I'll have to dig them up. Or I can delete my post until I have proof, no worries.
I was not referring to you Don. I am just talking about all the theories Frank puts forward.
 

DonH56

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Oh, well, I found it anyway. I did (do) not see Frank's posts. My little paper is not definitive because (among other things) the source is ideal so normal IR losses and slew-limiting that happens in the real world are not included. It is just an example pointing to what can happen. I think one of the corrections is to realize that the current bandwidth is not limited to 60 Hz...
 
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RayDunzl

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Just to say ... to me that's a disaster area, in terms of getting the quality of sound I chase - it's like a Ferrari that someone has fitted with old, second hand, unmatched tyres, with air pressures completely wrong - and then expecting it to "perform" ...

upload_2017-3-10_17-24-36.png
 

Blumlein 88

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OK, but I'll have to dig them up. Or I can delete my post until I have proof, no worries.

Oops, found the paper, see attached.

Not only what you have shown, but if you look at diodes turning on and off with an Oscope you can see they sometimes have nasty things going on. They don't turn on and off like a clean switch (heck even switches have bounce to the contacts). Much higher frequency even if low in level. If that gets high enough in level then perhaps a power cord could act as some sort of half ass filter I suppose. Yet with good gear I don't see any of this show up where the output signal is.
 

March Audio

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Meanwhile, what caught my eye when I first saw the DTCD stuff, after eyeballing the huge test currents, was this:

GeometryCom.jpg


The 'real world' consideration led me to think about diodes (rectification) and transformers (step-down would be typical)...

My imagination on this:

During the AC cycle the voltage applied to the transformer rises, and at some point the voltage produced at the secondary begins to rise above the stored voltage in the filter capacitor, and begins to forward bias the diode in the rectifier, which begins to permit current to flow into the filter cap.

Not a huge on/off current dump pulse. but a slowly (at the microsecond time frame) increasing forward bias on the diode, that raises the voltage in the cap, that reduces the forward bias on the diode, which throttles the current flow into the capacitor.

The greater the step-down ratio of the transformer the less abruptly the voltage rises in the secondary, slowing the turn on of the rectifier diode even more.

Rendering the fabulous pulse carrying capability of the Black Mamba moot.

I could probably fool around with a sin table and figure out the voltage change per microsecond for the degrees in the AC cycle of interest... but it would be a bit fumbly.

Maybe someone here has the tools and could simulate a simple power cord/transformer/rectifier/capacitor/load just to put some numbers on what 'really' goes on.

Yep this is a point I was going to make. The cap charging will have a time constant dependant on various factors.

I have a scope current probe so I will try and borrow a suitable amp to measure and show the current flows, but I suspect it will be somewhat like a lop sided triangle wave.
 
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March Audio

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Not only what you have shown, but if you look at diodes turning on and off with an Oscope you can see they sometimes have nasty things going on. They don't turn on and off like a clean switch (heck even switches have bounce to the contacts). Much higher frequency even if low in level. If that gets high enough in level then perhaps a power cord could act as some sort of half ass filter I suppose. Yet with good gear I don't see any of this show up where the output signal is.

Yes, there will be some spikes.

Also there is only one place where this is relevant. Any well designed low signal level sections in plyers or amps should be using a regulated supply. However power amp seections rarely do. Having said this they still require good power supply rejection as part of their design, particularly due to using an unregulated supply
 

DonH56

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Not only what you have shown, but if you look at diodes turning on and off with an Oscope you can see they sometimes have nasty things going on. They don't turn on and off like a clean switch (heck even switches have bounce to the contacts). Much higher frequency even if low in level. If that gets high enough in level then perhaps a power cord could act as some sort of half ass filter I suppose. Yet with good gear I don't see any of this show up where the output signal is.

Diodes have charge storage but don't have the gain to go inductive like transistors (except for lead inductance, usually tiny in this application). The big glitches usually come from current spikes hitting the transformer, which looks inductive and thus causes voltage spikes (v = L * di/dt). Those can get coupled back on the power line, and are often touted as being suppressed by the power cord salesmen, but as you say those spikes are suppressed handily by the power supply decoupling (filter) capacitors so the actual audio signal doesn't (significantly) see them. I should have thrown in a transformer model but oh well. (I actually thought I had, and am sure I have a few sims around with a transformer model, but couldn't lay my hands on them quickly.)
 

tomelex

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I don't get what you mean by "up to depending on impedance"?

Note peak currents from the line, which can be rather large and rather fast, depend heavily upon the power supply as well as the amplifier's design, signal, and the load. I did run some simulations a while back that I believe are posted over on WBF. That said, I have not measured them recently, but may try to grab one of our current probes and a DSO from work sometime to check it out.

Finally, a power cord can have some influence on the sound by filtering noise right at the point of service and of course supplying additional current if the stock cord is too small (unlikely IME). But those cases smack to me of poor component design...

I had said:
tomelex said:
So, looking at current used in the load, if you have 100W into 8 ohms about 3.5A, and into 4 ohm about 5A. So, if you are listening at 1W and you have a 10X peak, you are up to depending on impedance somewhere between 3.5 and 5 Amps.

This was just to point out that at the actual load, for 100W we were not really using that much current, to contrast to the OP about how they measured using huge current draws from the line, sorry, not clear on that Don.
 

March Audio

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I had said:
tomelex said:
So, looking at current used in the load, if you have 100W into 8 ohms about 3.5A, and into 4 ohm about 5A. So, if you are listening at 1W and you have a 10X peak, you are up to depending on impedance somewhere between 3.5 and 5 Amps.

This was just to point out that at the actual load, for 100W we were not really using that much current, to contrast to the OP about how they measured using huge current draws from the line, sorry, not clear on that Don.

Oh and don't forget that is transformer secondary side, stepped down from 240 or 110 volts.

So on the primary side its going to be a lot less. Lets say in the case of a 50v supply rail in a power amp / by 2 or 5 :)
 
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