Why an AC Power Cord cannot make a difference

[Devnull]

Are those the dangerous high voltage sort of circuitry? The stuff one cannot stand outside a live cabinet within maybe 1m with the door open and the circuitry energized?

It depends on the voltage and what you consider dangerous. You can go larger than 600hp with 480 3phase. Not inherently dangerous exposed, but nice to have in a cabinet if something does go wrong.

I think you're probably thinking about switch gear. Chain metal suits, fr clothing, remote trigger on off, plexiglass shields with long poles. As an example the water plant my neighbor works at gets 7500V 3 phase 100A redundant service. The backup generators they have are 12.5 KV. 5 Genny's ranging from 2.5 -4.5 MW. They can mix and match internal and external power through a bunch of switchgear and transformers in a few different rooms. That's when voltages get dangerous like you see on YouTube

 

[HaveMeterWillTravel]

Disambiguation from context: Variable Frequency Drive to control speed of AC motors, not the Vacuum Fluorescent Display that's probably more familiar to most here.

Heh. Yea, for any acronym one uses, there will be another relevant meaning as well.
OTOH Fluorescent lighting can put out some serious EMI (due to the ballast).

 

[Doodski]

It depends on the voltage and what you consider dangerous. You can go larger than 600hp with 480 3phase. Not inherently dangerous exposed, but nice to have in a cabinet if something does go wrong.

I think you're probably thinking about switch gear. Chain metal suits, fr clothing, remote trigger on off, plexiglass shields with long poles. As an example the water plant my neighbor works at gets 7500V 3 phase 100A redundant service. The backup generators they have are 12.5 KV. 5 Genny's ranging from 2.5 -4.5 MW. They can mix and match internal and external power through a bunch of switchgear and transformers in a few different rooms. That's when voltages get dangerous like you see on YouTube

That's serious stuff for sure. I've been inside a operational hydroelectric dam(s) and that was pretty intense at 60Hz but VFD interests me more.

 

[HaveMeterWillTravel]

It depends on the voltage and what you consider dangerous. You can go larger than 600hp with 480 3phase. Not inherently dangerous exposed, but nice to have in a cabinet if something does go wrong.

I think you're probably thinking about switch gear. Chain metal suits, fr clothing, remote trigger on off, plexiglass shields with long poles. As an example the water plant my neighbor works at gets 7500V 3 phase 100A redundant service. The backup generators they have are 12.5 KV. 5 Genny's ranging from 2.5 -4.5 MW. They can mix and match internal and external power through a bunch of switchgear and transformers in a few different rooms. That's when voltages get dangerous like you see on YouTube

VFDs and the semi-similar PWM drives scale across the gamut. As a family they offer significantly greater efficiency than standard line frequency AC motors or variable DC motors. They are representatives of AC loads where the input current waveforms are characterized by small duration but high amplitude "gulps". Their output waveforms can be even worse.

If you replace your HVAC with a modern high-SEER there very well maybe one there. Computer fans are often PWM. But buy a cheap ceiling fan motor off Alibaba and you may have introduced the equivelent of a screaming baby of the EMI world into our life.

But to keep relevent to home audio, traditional "power line filters" using basic caps and inductors tend not to work nearly as effectively as they do on more traditional power loads. In fact, the excessive ripple current can wreck havok with the capacitors.

Luckily, most decent brands have either integrated active current injection filtering on their input stages, or offer a companion to the VFD.

It's just an example of power line disturbances far greater than "power cables" can handle, but in a non-audio industry which scientifically approaches the problem and has sound engineering behind their solutions.



HMWT

 

[EJ3]

Are those the dangerous high voltage sort of circuitry? The stuff one cannot stand outside a live cabinet within maybe 1m with the door open and the circuitry energized?

But when the door is shut, you can use it for a seat, right?

 

[Doodski]

But when the door is shut, you can use it for a seat, right?

I use them for foot warmers and for roasting weenies. Hehe... In all seriousness I was touring a lab and they had new VFD high voltage drives on soak/test and I went about 2m from one with the door open and they where very concerned and ordered me to step away.

 

[HaveMeterWillTravel]

It depends on the voltage and what you consider dangerous. You can go larger than 600hp with 480 3phase. Not inherently dangerous exposed, but nice to have in a cabinet if something does go wrong.

I think you're probably thinking about switch gear. Chain metal suits, fr clothing, remote trigger on off, plexiglass shields with long poles. As an example the water plant my neighbor works at gets 7500V 3 phase 100A redundant service. The backup generators they have are 12.5 KV. 5 Genny's ranging from 2.5 -4.5 MW. They can mix and match internal and external power through a bunch of switchgear and transformers in a few different rooms. That's when voltages get dangerous like you see on YouTube

If an E/M field can be strong enough to self-light a fluorescent bulb; could you fashion a 'free energy' tube amplifier?

 

[Devnull]

If an E/M field can be strong enough to self-light a fluorescent bulb; could you fashion a 'free energy' tube amplifier?

Don't know. What might be interesting would be find a friendly farmer with transmission lines running through his fields. Run a nice long wire parallel to them and see what kind of voltage and current you get.

 

[Punter]

I wrote my first technical post on ASR to dispel the power cord myth so I completely agree with the OP. It's always amusing to see the believers pop up and then disappear on these types of threads. As soon as the members start asking for more details and, and ... you know..... evidence, they just fade out . Even if you have only a basic understanding of electrical theory the proposition that a simple mains cable could alter the quality of the output of an audio amplifier is preposterous. As I pointed out in my article, the energy going in to the amplifier power supply is fundamentally changed from alternating to direct current. The mains cable merely delivers the AC to the input of the power supply and provided it does so without any significant electrical resistance, it's done its job. That's it, period. From there, it's the job of the power supply to provide ripple free (or as close as possible) DC to power the amplifier circuits. The amplifier can't actually "see" the mains cable, the power supply is a buffer in this respect. Thus it's a physical impossibility for the mains cable to influence the amplifier in any way if it's up to code for the power required.

So this sort of thing is absolutely hilarious! Oh, 4200 Euros by the way.

LINK to review

 

[Doodski]

the power supply is a buffer

Sort of get what you mean. The power supply smooths AC to DC and has a output impedance. In the case of a power amp the output transistors vary via a voltage divider the power supply voltage output and the output transistors voltage output. This varying impedance of those 2 sections causes the output voltage and current at the speaker terminals to rise and fall as we see. The lower the output impedance of the power supply the more current can be delivered to the speaker providing the output transistors can do that too. I'm not so sure buffer is a proper term for the operation but I do get what you mean. I would be more set to call it the smoothing section, the filter section or just power supply.

 

[Cbdb2]

The backup generators they have are 12.5 KV. 5 Genny's ranging from 2.5 -4.5 MW. They can mix and match internal and external power through a bunch of switchgear and transformers in a few different rooms. That's when voltages get dangerous like you see on YouTube

Only if they can provide current. Some car coils can put out 30kv but they wont hurt you. You can get 10kv from rubbing your runners on a wool carpet.
Whatching the lightning (10' arcs from Mvolts) in the EE high voltage lab at uni was always fun and scary at the same time.

 

[Cbdb2]

I'm not so sure buffer is a proper term for the operation but I do get what you mean. I would be more set to call it the smoothing section, the filter section or just power supply.

If you consider that the power supply is only connected to the mains only 10 percent of the time, during the charging pulses ( disconnected by the reverse bias diodes), in normal operation you can think of the PS as a power buffer.

 

[antcollinet]

Are those the dangerous high voltage sort of circuitry? The stuff one cannot stand outside a live cabinet within maybe 1m with the door open and the circuitry energized?

They can be. The ones I participated in the development of were typically 400 to 480V units with up to about 900V of DC link in them. Reasonably safe if you didn't try to poke a screwdriver in through the vent holes.

 

[Doodski]

If you consider that the power supply is only connected to the mains only 10 percent of the time, during the charging pulses ( disconnected by the reverse bias diodes), in normal operation you can think of the PS as a power buffer.

I see.

 

[antcollinet]

Some car coils can put out 30kv but they wont hurt you.

Just like electric fences they shouldn't kill you (assuming your heart is otherwise healthy), but believe me they can 'kin hurt. DAMHIKT

 

[egellings]

Believers in a cord like that will buy it, connect it up to the system and believe that they hear a different, hopefully an improved, sound. So for them it worked. They got what they wanted and like it, even though there's no evidence of any real effect on sound quality. It's like alternative medicine quackery.

 

[Salt]

Just like electric fences they shouldn't kill you (assuming your heart is otherwise healthy), but believe me they can 'kin hurt. DAMHIKT

did'nt p. on it, did?

 

[antcollinet]

did'nt p. on it, did?

No, not that bad. But I have been dumb enough to try to stop a lawnmower by pulling the HT lead off the plug.

And I had a mate who lived on a farm. So inevitably got a few jolts from the fencing.

 

[Doodski]

I have been dumb enough to try to stop a lawnmower by pulling the HT lead off the plug.

I did that too with a redlining CanAm 250 Qualifier dirt bike. The throttle was stuck and I had a big idea....lol. It put me down.

 

[HaveMeterWillTravel]

I wrote my first technical post on ASR to dispel the power cord myth so I completely agree with the OP. It's always amusing to see the believers pop up and then disappear on these types of threads. As soon as the members start asking for more details and, and ... you know..... evidence, they just fade out . Even if you have only a basic understanding of electrical theory the proposition that a simple mains cable could alter the quality of the output of an audio amplifier is preposterous. As I pointed out in my article, the energy going in to the amplifier power supply is fundamentally changed from alternating to direct current. The mains cable merely delivers the AC to the input of the power supply and provided it does so without any significant electrical resistance, it's done its job. That's it, period. From there, it's the job of the power supply to provide ripple free (or as close as possible) DC to power the amplifier circuits. The amplifier can't actually "see" the mains cable, the power supply is a buffer in this respect. Thus it's a physical impossibility for the mains cable to influence the amplifier in any way if it's up to code for the power required.

I consider "physically impossible" an overstatement which has not been supported in this thread and is bordering on proselytizing.

There are a few trivial but obvious examples where there can be profound (easily measurable and audible) differences. Those cases are well understood and there is nothing 'magical' about it.

Additionally, if "power is power" why is there a whole science behind properly engineered IEC power receptacles with integrated EMI filtering?

There are also various known and unknown edge cases which only apply to a very narrow set of circumstances as well.