Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems Power cables into DSP's...not the snakeoil or fact question

Hi George,

I didn't get chance to do that. All the time available was spent at the DSP end.

Unfortunately, I'm away again with work and the cables are on their way back to Nottingham.

Time for a hotmail backup account for you I reckon.

For you Nick - taken from the 'gon:

11-29-05: Serus
The following is my engineering interpretation of power cord contribution to good sound. If you have to ask, then I also didn't think they'll make a difference, but reality strikes, my friend!
I've heard amps distorting big time with certain (expensive!) power cord while other amps sounded great with the same. Nothing wrong with either amp!
So why is it?
If you interpret power cords as extension of the "miles and miles" of Romex, inevitably it sounds real dumb that they'll make any difference.
Here is what they are: they are the piece of wire that is closest to your equipment. BIG DIFFERENCE.
Why?
Because audio equipment is affected by NOISE. It's supposed to amplify 20 Hz to 20 KHz, but the circuit doesn't know that!
Audio circuits pick up radio frequency and "mix" it with the audio. This is no technical mumbo-jumbo. Just ask any RF engineer about intermodulation with circuit non-linearity and they'll pull a stack of papers on the topic. Very scientific.
The "funny" thing about radio frequency is that it radiates from antennas and picked up by antennas. The antenna has to be related to the wavelength of the RF emmisions, so short wires are almost "perfect" for that. Yucks!
Well, you might say, there is no short wire. It's an extension of miles and miles. Not so!
When it comes to very high frequencies, the wire's miniscule inductance (very scientific - check technical specs!) is large enough to make the far end of it irrelevant. That's a great simplification, of course, unless one wants to solve Heavyside/Maxwell equations. I don't recommend that...
Now that we understand the nature of wires in close proximity, perhaps we'll be more open-minded about the effects of these wires on the system.
Now, those of you in the rural area might think that they don't have RF pollution to worry about... Wrong!
Guess what. The power supply in any equipment is a source of RF noise. Ahh?! Say what?!
If you have a high speed scope, pull it out and sample (at your own risk!!!!!!!!!!!!!!!!) the rectifier diodes at the switching point. Zoom in and enjoy the view!
There are several mechanisms in which RF pickup muddies audio. One was mentioned above - direct mixing. The most common might be the impact on jitter in digital audio sources. RF has its nasty ways of leaking through stray capacitance. In average equipment it takes very little effort to reach clock circuits and add a few nanoseconds of "fuzziness" to your timing reference. This topic has been analyzed to great boredom, so just search for exact details. The jist of it is that very few nanoseconds of jitter are enough to cause distortion of the non-harmonic type - the worst there is. Audible products that do not relate to the music tones!
If you don't accept that jitter is an issue then you are seriously wasting your time reading all the way to this point. It's too scientific, perhaps.

So now we understand three things:

1) short wires in close proximity to the equipment differ from miles of Romex in regard to RF rejection (elementary Physics).

2) Any system with a power supply emmits RF. (you can verify this yourself - again: at your own risk!!!!!)

3) Low levels of RF mixed with audio are not nice. (Just ask any RF engineer)

Any more comments about the "myth" of power cords?!
Mind you, I don't advocate paying $2,000 for these, but at least be aware that they are doing something other than draining your bank account. Some power cords do RF filtering extremely well!



11-29-05: Serus
This is a minor correction to my last post in this thread.

Jitter is measured in picoseconds, not nanoseconds. That's how sensitive clock circuits are. Jitter in the order of 300+ picoseconds already has a major impact on sound quality from a digital source. You'll hear that as a "fuzzy" imprecise soundtage.
One picosecond is one milionth of one milionth of a second, or ten to the minus twelve for you techies...
You don't need much to cause harm!

Some folks assume that since scientists know a lot about delivering voltage and amperage that scientists also well understand how different "qualities" of power delivery affect human hearing. In my opinion we know more about the eye than we do about the ear. We have far to go in having as sophisticated a model for hearing as we do for sight. This coming from someone who has experienced dramatic, negative side effects from laser eye surgery!

That said, the water/hose analogy really falls short rather quickly because you have to consider concepts such as dielectric qualties of wire casing (i.e., the changes to the wave nature of the electric current), skin effects, RFI, EMI, and physical vibration. Remember, electrons have both a particle nature and a wave nature. The folks who focus predominantly on the particle nature of electricity are losing sight of an equally large, if not larger, contributer to the quality of sound in a playback system.

Another reason the water/hose analogy is not correct is because in that analogy, the timing of the delivery of the water molecules is not considered because it is not relevant. However, with electricity, it is entirely relevant. The mistiming of electrical information is called jitter, and it can have a profound effect on the percieved speed and detail of music. Have you ever heard a playback system that had really slow bass, even with those without a subwoofer? Ever wondered why? Typically slow bass can be amerliorated with better cabling, which can lower the noise floor and reduce jitter through shielding, adding filtering networks, using different materials, different winding patterns, and other techniques. Mark_H is correct that there is a significant cumulative degenerative effect from the propogation of each individual component's noise to the entire system. So, if you can't tell, I am firmly in the camp with Nick and Mark_H.

Another point, in my opinion, Meridian makes the best multi-channel gear available anywhere. However, there are quite a few pre-amps that better my 861v4 in 2-ch playback. So, please don't fall into the faulty logic that everything Meridian does is near-perfect, so if they don't use the highest quality part or employ a particular technique, that it must be trivial, unimportant, or wrong. To do so reflects a lack of open mindedness and a lack of experience listening to different systems. Tassie_Devil's experience with improving the performance of his 800 with modifications speaks to this.

If anyone is travelling in the Baltimore/Washington DC area, you are welcome to listen to my system to hear the effects of different cabling, in a well tuned system. I will travel to Virginia, Delaware, Pennsylvania, and New Jersey to prove this point as well. Any takers?

Damon

I can't hold back any longer. Must spod!

The psu in your speakers converts 100-240V AC to a series of DC voltages as has been said above. You'll normally see 5V (and nowadays 3.3V, 2.5V and 1.8V and even 1.2V) for digital. The low power analogue normally runs off about +-15V, and the power amps use higher voltages to keep the current reasonable (+-30V to 60V).

All these are DC. This is how it gets converted (and this is important).

1) First a transformer reduces the voltage to the intended values.

2) A rectifier circuit converts the 50/60Hz AC to a pulsed half wave 100/120HZ DC (technically) supply.

3)

And??? Don't die of excitement half way throgh!!!

Oops - hit the post button too early!

The wave at the transformer output looks like:

_ _ _ _ +V
/ \ / \ / \ / \
\_/ \_/ \_/
-V

The wave at the rectifier output looks like:

_ _ _ _ _ _ _ _ +V
/ \/ \/ \/ \/ \/ \/ \/ \ _
0V

3) A smoothing capacitor smooths the pulsed double frequency into a steady DC at the RMS value of the wave.

The key thing is how the rectifier keeps the capacitor 'reservoir' topped up.

They're made out of diodes, and diodes conduct current in only one direction, so they only conduct when the voltage on the capacitor is lower than the voltage at the transformer output.

This difference is the 'ripple' of the supply. It's a bad thing. It increases the more current you draw from the capacitor, and decreases with bigger capacitors (they lose a smaller proportion of their charge before being topped up).

So, for a given current output, a bigger capacitor gives you a more stable supply, with less ripple.

Here's the problem, though. A big capacitor still only has the time where it's at a lower voltage than the transformer to be topped up. This means that it pulls a HUGE current through those diodes (actually only two at a time). That's why they're so big.

So here's the point:

A linear power supply, in the process of working, converts your relatively smooth 50/60Hz voltage into absolute horror of a current. It sits their doing nothing, then pulls all the current it needs in about 5% of the available time.

If it helps, think of a reservoir with a dam at the low side. Water (current) is allowed to drain out of the dam at a steady rate. The faster the water drains out, the more the 'loading'. Now top up the dam to its full mark once every minute, but you only have 5 seconds. You'd need to throw in a lot of water!

(A bigger capacitor is a wider and longer reservoir - might be time to stop stretching this metaphor!)

A normal linear PSU couldn't give a rat's about the quality of the mains, because it looks bloody awful anyway as its converted. That's what the caps are there for. (Mind you, spikes can get past at times).

But then again (as a mate of mine who designs BIG power supplies says). Imagine what is happening to the mains for the rest of your equipment whilst the power amp is pulling those big pulses from the supply. I think that's one of the arguments that one of the manufacturers of conditioners uses. It's there to protect the rest of your kit from the mess that the power amp is making of your supply. Then again, if they also use linear power supplies, then they also are isolated from a lot of the noise.

Personally, I think I'd need to upgrade a hell of a lot before I get a conditioner. And I'd be thinking of getting a posh mains cable when the local electricity board use OFC for their network :-)

Having the power amp on it's own spur from your distribution box might help, though.

Or even - having all of the delicate electronics (analogue, DACs, clock sources) on the smooth side of the supply, in the same box. I reckon that Bob Stuart might be on to something with these active speakers! :-)

Just another couple of pence. If I add these up, I'll be ablew to get that 568 I keep promising myself!

End of sciency bit!

Cheers,
Mark.

Ultima_gtr,

That's a great read......I take it then that you are in the snakeoil corner then ?

DANewsome,
Thanks also for your input. Equally interesting.

Both spot on with what I was wanting to get to. Now...

Would you two guys mind slugging it out for a while to see which theory gives in or indeed if the converge ?

Blue corner is snakeoil & capacitors
Red corner is dielectrics etc

Mr Meridian,

I nearly did! :-)

Apologies for the state of those waveforms! The first is supposed to be a sine going from +V to -V, and the second the same signal, but with the bottom half mirrored up to be a double frequency signal going from 0V to +V.

This has been a spectacularly fast moving thread and fun to follow. I'd even say it's been educational but I can't claim to properly understand all the "sciency bits". It does seem a bit like "when science meets religion", though (agnostics, atheists, deeply committeds, converts....)

Nick, why did you decided to keep your money in your pocket? Is it because the sound wasn't preferable or because the change lacks credibility or something else?

I can't add to the erudition here but I'd offer the observation that Naim and Cyrus, to name but two, offer external power supplies as upogrades to their products and I've heard of none who say there is no improvement. I've mucked around in a very limited way with Isotek and Missing Link products. They make my system sound different (it needs all the hi-fi reviewers jargon to describe it, though). As a result of the mucking around, I will spend money on Missing Link products before I upgrade my 598 or 568.2

A question: Mark at The Missing Link tends not to make claims for their products but he thinks they make a difference worth owning. Does he take this stance because there is no sustainable scientific justification or, perhaps, because the snake oil market is big enough and forgiving enough?

Regards,
Steve

Its like the language of wine, Jilly Goulden talking of a bouquet of "tarmac" with a hint of "welly boot"

I can never find the words but i do know that with a little instruction a good �7.00 Bottle will be far more satisfying than a �1.99 Special.

After that its all a matter of dimminishing returns, unless you think it isn't of course.

Enjoy Hic!! Chris

P.S. A good Shiraz would make a great upgrade, then for comparison you may wish to try a Pinot Noir.
The rest you can work out for your selves. Enjoy!

Oooh OK!

I should say at this point that I'm quite happy to be wrong. Best way of learning. Perhaps there are better ways when others are watching, but it'll do.

The wave/particle duality of electrons is pushing it (in my limited experience of physics). You use the one that you're probing at the time. Maxwell's equations work the same for electrons as they do for deBroglie electron waves. You start firing them at a double slit, you'll see the wave. Count them coming from the back of a CCD from light quanta, and you'll see particles. I think I saw them described as travelling as waves, but arriving and leaving as particles, which seems pretty accurate.

Jitter is a problem, and I'm constantly amazed at how low some manufacturers claim to get it (I suspect serious spec manipulation). But in any well designed circuit you should design things to reject power supply noise. I do accept that perhaps the largest source of jitter for a VCXO is PSU noise to the oscillator, but that is far more likely to be caused by PCB layout and poor decoupling than a deficiency in the power supply.

I think someone else invoked the distributed model of a conductor (little aerials). This is why you have decoupling capacitors on the PCB. They are a low inductance current source to filter local power supply problems. The power supply itself is a long way away (electrically), and is largely irrelevant at high frequencies.

Sometimes in hi-fi, we have a tendency to invoke magic. The state of the art for production serial links is 10GHz. 96kHz audio is 2.8MHz. The same laws that keep those links working (and those Boeings and Airbusses in the sky) apply to the hifi stuff too.

Skin effect is real, but it actually helps you from a noise perspective. It raises the effective resistance for high frequencies because they only travel on the skin of the conductor. It's only a problem when you're trying to send really high frequencies across solid core wires.

Jitter, DAC resolution and sample rate all apply to mobile telephone base stations. But here they tend to use 16 bit, about 50MHz sampling and oven controlled oscillators to reduce jitter. Any noise means poor efficiency, which costs a lot of money (see 3G licences!). They don't use oxygen free copper or green permanent markers. (or DACs with a real resolution way below their quoted number of bits for that matter). Just sound engineering practice, and it works.

I've also seen some pretty good data on human hearing. It's a lot better understood by psychoacousticians than people give them credit for. Did you know the shape or your ear isn't there to collect sound? It's there to alter the sound coming from different directions in a complex, but repeatable way. This is the head-related-transfer function. And early research in virtual reality led to those surround headphones you can get now. That's pretty subtle stuff.

Once again, it's nice to have these discussions. No matter what anyone's side, at least they care about their music enough to care!

Regards,

Mark.

I think the idea of Radio waves broadcast by the power cable and received by the circuitry inside the speaker could account for the difference. I wonder why some cables are much more affected by this than others. One reason that I like this theory is that it is very testable. You could take the crappiest cable you can find and try it with and without any shielding. You could just use some unsightly but effective shielding and cover the cable for testing.

I have to admit that my suspicions are that the differences in power cables are due psychology and not physics. But I think it deserves a thoughtful debate, and some testing.

I do wonder why hi-fi equipment is so affected by mysterious effects and no other appliance in my home is? I have a very sophisticated Epson 4800 ProStylus printer. I have never read about anyone getting better prints from using a different power cable. The same holds true for every other appliance that I have had the opportunity to work with both commercial and industrial. I do not dispute that appliance need to be shielded from RF, the government requires all such devices to pass tests and be certified before they can be sold.

Is it because of physics or psychology?