Power cable question

[mort]

I was having a conversation with a guy about those 'high end' power cables that promise to improve sound and clarity in the output of guitar amps. My first inclination was to think that the only improvements to power cables would be for durabilty's sake.

I brought this up to an electrical guy at work and he came up with a couple other possible improvements. He said that stray noise could partially be removed from the line signal by having a ring magnet around the hot leg and another one around the neutral, pulling some stray electrons off of the current? Also he mentioned having a capacitor in parallel to one or both legs(?). According to him the only way to remove *most* of the noise is by having a transformer with isolated or 'floating' ground, as is the case with medical equipment and other sensitive applications.

Anyone care to comment on the plausibilty of these ideas, or have anything further to add about improving a guitar amp's sound with the power cable?


(I have no desire to buy one of these 'high end' cables. It's just an interesting topic)

[Intergalactic Tourister]

Also he mentioned having a capacitor in parallel to one or both legs(?).

An "across the line" and/or "line to ground" cap can easily be installed inside the amp. Shielding is already in regular 3 prong cords.

[mort]

An "across the line" and/or "line to ground" cap can easily be installed inside the amp. Shielding is already in regular 3 prong cords.

So these 'high end' power cords are 100% hogwash? Or could they potentially only be 95% hogwash?

[Intergalactic Tourister]

Reminds me of the clothes hanger wire vs. monster cable wire a/b test.

Hogwash? No.

Probably more about cost/benefit. The price of the cord relative to its actual (or marginal) utility.

All season radial tires will get you to work on time. However, for thousands more you could use cheater slicks and think you'll never be late.

[Chuck H]

The thing is, none of these expensive cables have ferrite rings or capacitors in their design. They're just high strand count heavy gauge cables. Good cables to be sure. But no sound difference. You see ferrite rings on things like Dremel tools and occasionally cell phone chargers. We're talking MHZ. At audio frequencies the power cable does NOTHING. The only exception being if it's so grossley small that it can't support the current demand or of such poor quality that it's in danger of breaking and shorting.

JM2C

[Dave Curtis, dB AudioTech]

"Shielding is already in regular 3 prong cords."

"Regular" AC cordsets aren't shielded.

You'll see those X (across-the-line) and Y (line-to-ground) caps in this schematic:
The Free Information Society - Peavey Micro Bass Electronic Circuit Schematic

These are special (safety) caps designed so that if (when) they fail, they won't short, like the "death caps" did. They have a bunch of listing agency's marks on them like these:

[Intergalactic Tourister]

"Shielding is already in regular 3 prong cords."

"Regular" AC cordsets aren't shielded.

About 85% of the 3 prong cords I've come across have been shielded. And many of those cords even have a fourth bare wire that can be grounded from the cords internal shielding to the amps chassis. So regular as in my regular, I guess.

But yes, not all cords have shielding.

[Steve Conner]

I've seen one shielded power cord in my entire career as an EE.

[R.G.]

I brought this up to an electrical guy at work and he came up with a couple other possible improvements. He said that stray noise could partially be removed from the line signal by having a ring magnet around the hot leg and another one around the neutral, pulling some stray electrons off of the current?

By "ring magnet" I take it he meant ferrite/ceramic rings. It is possible that this could add some small filtering to the wires by introducing more inductance. The amount of inductance is small, and permanent magnets make poor inductor cores, but this is the grain of truth hiding in there, if any.

I cannot fathom "pulling stray electrons off the current" on a technical basis. In a metal, all the movable electrons are loosely shared by all the atoms. This is in fact one of the things that makes a metal be a metal. This "sea of electrons" can be pushed/pulled one or the other direction by voltages. They really can't "stray", and they can't get out of the wire, so pulling stray electrons out of the current makes no technical sense to me as I understand the physics involved.

Also he mentioned having a capacitor in parallel to one or both legs(?). According to him the only way to remove *most* of the noise is by having a transformer with isolated or 'floating' ground, as is the case with medical equipment and other sensitive applications.

As noted, capacitors between the line and neutral wires does help shunt some high frequency noise that would otherwise get through. So does a capacitor from BOTH of line and neutral to safety ground, for a total of three. Putting inductors in series with both hot and neutral wires, AND a common-mode inductor on both line and neutral can be the basis of a line filter, and this does help get rid of hash, buzz, RF, ticks, spikes, etc.

It does nothing at all for hum issues. It can't. The power line frequency is the same frequency as hum. You can't filter out one without filtering out the other.

Transformers do help remove hum. They do this by making a completely floating secondary voltage which has no reference to the AC power line at all, and so cannot carry line frequency hum as a differential of both the line and neutral wires compared to the AC safety ground. Medical and other sensitive stuff does this, and goes even further with a grounded shield inside the transformer.

Transformers can, as coils of wire, pick up hum that's radiated as a magnetic field, so unless you're careful, they can cure one hum and make another worse.

Anyone care to comment on the plausibilty of these ideas, or have anything further to add about improving a guitar amp's sound with the power cable?

The law of diminishing returns has a heavy hand. Once you're carrying enough power into the amp, further making easy for power to get in is mostly futile. Solid silver cables a foot thick won't help provide more power. As to providing cleaner power, The process of rectifying the transformed AC and making DC out if it is already a powerful mixmaster blender on what's coming in through the AC line. Since a fancy cable is before this grinder, it cannot help make the output of the grinder much "purer".

And it's for sure that bigger or better or special power cord wiring can't reach through the amp's power supply and make the guitar sound sweeter.

Shielded power cables are commonly available. They were developed to prevent noisy switching power supplies from radiating RF noise using the AC power line as an antenna. Most computer-specific cords used to be shielded. If you needed another couple of DB lower RF emissions to pass the radiated RF specifications, this could help do it. It's the same reasoning as putting a ferrite lump on the power cord - the ferrite lump makes for an RF choke, the shielding on the power cord is a shunt capacitor which helps force the leaked RF to stay inside the chassis doing the generating.

[tedmich]

my current favorite


Stage III Kraken REFERENCE AUDIO POWER 1.5 Meter

$8800 !!

Stage III Kraken REFERENCE AUDIO POWER 1.5 Meter - True Audiophile


True Audiophiles LAUGH at the piteous pretense of guitar snobs!

[Chuck H]

I read that those can make a real difference in your bottom end. It gets lighter. Especially around the wallet area.

[Dave Curtis, dB AudioTech]

A few years ago, I picked up some 8' shielded IEC power cords; I think they were like $3 each. I haven't done a double-blind test or anything, but I'm pretty sure I don't care if they "sound" worse than an $8K cord with electron-aligning meconium diodes...

[clyde1]

OOh, carbon fibre!

[Martin Pedder]

I've seen one shielded power cord in my entire career as an EE.

In the 1980's, the BBC used to use the LNE mains XLRs on many pieces of equipment. NEUTRIK XLR LNE FC They would often be wired with a BBC spec mic cable that had mains rated insulation and a braided screen. As all studio gear was balanced and had a separate safety (chassis) earth and technical (earth) it meant that hum fields were low. The majority of audio wiring was done with twisted pair, overall screen multicore; PSN10 (5 pair), PSN20, (10 pair) etc. Individually screed multi-pair was generally only used for mics or in high RF areas like OB vehicles.

I loved the idea of keeping the technical ground isolated. Broadcasting House in London had the main technical earth in the basement. It was (probably still is) an enormous coper pipe running down into what I believe was originally an artesian well under the building. It was connected to a massive copper plate on the wall, from where monster multi-strand technical earth cables ran to all the different floors to split out to the various technical areas.

Of course, it would only take one piece of equipment in the whole building (11 floors with the basements) to bridge tech and mains earths. Just patching an earthed piece of domestic equipment into a studio patchbay would do it. So, each studio had the facility to disconnect the incoming earth so we could test for anything bridging mains/chassis/safety earth to tech earth. They could be pretty tricky to find too. I found one once where the body of an electret talkback mic in a console had moved slightly so it was touching the metal panel of the meter penthouse. Checking this on a regular basis kept the technical earth very clean.

It meant that, where they weren't building their own, the BBC usually had a special version of all the equipment they bought. Where the manufacturer wouldn't do this, any non-pro equipment bought in had to be modified to separate chassis from signal earth. This often meant replacing PCB pillars with plastic ones, re-mounting external connectors, fitting an external signal earth binding post, fitting 1:1 audio transformers etc. Whether this is still done now, I couldn't say. You certainly don't see much pro gear these days with two earth terminals on the back and a metal bar linking the two (for non-broadcasters). So, when you see one, you will know the reason why.

[Steve Conner]

I worked as a trainee technician at BBC Scotland in Glasgow in the 90s. I remember those crazy red XLR plugs. I also remember being sent underneath the desk in the OB van to remove dodgy modules from the meterbridge.

Whether this is still done now, I couldn't say.

I think the days of the LS3/5A and the Radiophonic Workshop are over. I heard that they sacked all their engineers and outsourced all of the technical stuff to Siemens Broadcast. (could be an urban legend admittedly)

You certainly don't see much pro gear these days with two earth terminals on the back and a metal bar linking the two (for non-broadcasters)

We have one piece of lab equipment like that, completely unrelated to broadcasting.