Apple MacBook. Battery powered?

uglymusic

I know the received wisdom is that the laptops should be run on battery power. Have any of you tried listening with and without the power lead?

I ask, because I can't hear any sonic differences with my White MacBook. This could be because I believe the MacBooks take at least some of the power from the battery, even when plugged into the mains.

Gromit

I've found the same Dave - in fact I even thought of starting a thread myself about it. I really cannot detect any difference to be honest - and yes, the Mackbook does take some juice from the battery when it's plugged into the wall. The only downside, as a friend of mine who works for Apple in the UK told me, it actually doesn't do the battery any good to run the 'Book off the mains when it's fully charged (saying that I do it all the time!).

uglymusic

Interesting. Glad my ears haven't gone completely silly.

Again, the received wisdom is that you should run the battery down to zero once a week or so and that keeps it happy.

Alan

That's interesting stuff. I had though that the presence of a switch mode power supply (as chargers are) was the real culprit - the interference would therefore be on the mains rather than through the 'puter.

uglymusic

It's very interesting. And perhaps another argument to temper received wisdom with experience?

RobHolt

No difference with my Macbook Pro which is used primarily as a music server.

Signal connection is via optical or wireless so only the SMPS could have any effect., but it doesn't seem to.

uglymusic

I wonder what is going on?

I so far haven't been able to figure out a way of isolating the various factors at work here.

ItemAudio

I have a MacBook which makes an awful racket when plugged into the mains, and another one that barely makes a difference at all when connected.

You have to factor in the multiple voltage rails: the battery delivers nice clean 11-14V for bits of the mobo that need it, but switches / regulates it down to 5V and 3.3V for some processes and chipsets. So the switching noise you're looking to eliminate is right where you don't want it - after the battery - and remains largely unaffected by plugging into the mains in most cases.

uglymusic

So a Mac requires two PSUs, then, in an ideal world?

ItemAudio

In an ideal world, we need to abandon the Mac Mini power supply - which we measured as having 0.5V of noise on the output (!), and put tri-linear supplies in all our computers: it's the only way to fly.

And even then, you have to perform some serious damage limitation on all the outputs to tame noise introduce by the rest of the motherboard . . . this assuming you have already dealt with noisy peripherals and mains.

That's why our desktop DATs have three or four separate power supplies. And the new ones have five.

With a MacBook, the challenge is to quiet the monitor, and - ideally - inject clean 5V and 3.3V from modified batteries directly where it's needed. However, some motherboards require the correct voltages to be delivered / timed in a specific order on boot . . .

Given how much hassle all this is, the easiest DIY route to take is to remove all the noisy stuff, slather everything in Stillpoints fabric, galvanically isolate the USB or Firewire output and spend obscene of money on a clock if your DAC performs best on SPDIF or XLR - just like the pro audio crowd.

uglymusic

I'll borrow what I can on a DIY level.

As I said, the monitor is off, as are the wireless components. I know where the wi-fi is on the mobo - I saw that over the weekend - but I'll have to see if I can actually remove it. It's not like the little boards waving in the air inside a Mac mini.

I'll have a think about the Stillpoints fabric. How would I go about galvanically isolating the USB output, though?

The clock purchase is thankfully not relevant (phew!).

sq225917

@Ugly, Why would you want to isolate the USb output, the Young doesn't connect the power lines in the USB cable up and the signal input lines are al galvanically isolated internally to the Young with high speed transformers. There's nothing to be improved there.8->

Funny despite all the claims for noisy mobo etc, i've still not seen a single measurement showing power supply noise on a pc affecting the output to a DAC.

If a mac mini genuinely has .5v of noise on the output, and it happily runs a chip at 1.2Ghz or whatever frequency, it has to tell you that they have internally PSSR very well sorted.

Alan

I'll cause you to fall off your chair in surprise Simon, by saying I don't quite understand the last paragraph you wrote!

But on the (related) subject of MACmini power supplies, is it too much of a thread hijack to ask what benefit there would be to having a linear PSU made? In my mind, I had reasoned the improvements would be as much about removing a substantial switching supply from the vicinity of the hifi as any benefit to the computer. I beleive the mini draws 18.5v at 6a.

uglymusic

@Ugly, Why would you want to isolate the USb output, the Young doesn't connect the power lines in the USB cable up and the signal input lines are al galvanically isolated internally to the Young with high speed transformers. There's nothing to be improved there.8->

Funny despite all the claims for noisy mobo etc, i've still not seen a single measurement showing power supply noise on a pc affecting the output to a DAC.

If a mac mini genuinely has .5v of noise on the output, and it happily runs a chip at 1.2Ghz or whatever frequency, it has to tell you that they have internally PSSR very well sorted.

Just trying to get to the bottom of Mark's recommendations, Simon 

sq225917

Alan, the main improvement would indeed be not exposing other gear to the hash fed back from the SMPS rather than any improvement in the mini's performance.

re Mark's comment. If as he states the mini power supply has 0.5v of noise, (he doesn't mention if that is peak or RMS noise,) he doesn't  give a frequency band so let's assume it's RMS, then the Mini itself must be able to work without impairment from that noise. Effectively it can function with that noise level because internally it has additional power supply elements that filter the noise out, ie it's PSRR, power supply, rejection ratio, is sufficiently high to remove the noise from the switch mode.

The sound card and the CPU both operate from the same power supply input, one works at Ghz speeds and the other at Khz speeds. Which one do we think requires the best power supply filtration?

The CPU of course. So if that can survive with 0.5v noise then the sound card chips sure as hell can. The fact a mini/pro sound identical with power plugged in or on battery tells you the answer you suspect, it makes no difference. Don't be fooled into believing it does until can show you solid measurements displaying an effect. If they can and the level is within 10x of what we can hear, maybe give them the benefit of the doubt.

Read the Accuity stuff, they are talking about adding power supply, isolation and cables to achieve improvements in the order of -180db that's 10,000 quieter than you can hear- why worry?  ;-)

Alan

Thanks for taking the time to explain that - I can follow the principle of what you say. I am happy to adopt the pragmatic approach, as I use the mini also for DVDs, occasional interwebbing and other stuff - so it's not the hardcore unadulterated music server of a self respecting computer audiophile anyway!

Would adding something like this (link below) effectively isolate the main rig from the switching noise? It was recommended by a chap from computer audiophile, but I hadn't got round to trying it. I had been toying with the idea of a linear PSU.

http://cgi.ebay.co.uk/AC-power-line-filter-Hi-Fi-and-Hi-END-audio-DIY-/260748334535?pt=LH_DefaultDomain_0&hash=item3cb5cfd5c7

uglymusic

Read the Accuity stuff, they are talking about adding power supply, isolation and cables to achieve improvements in the order of -180db that's 10,000 quieter than you can hear- why worry?  ;-)

Have I missed something? What Accuity stuff? I've Googled and failed.

Alan

Have you Dave? That is very presumptuous of you. (Yes, I know it is a good word...)

uglymusic

It's hardly surprising I'm allergic to the little furry horrors, is it?  :-L

sq225917

I'd expect that to provide you with absolutely SFAl reduction in anything. Maybe 10-20db if the level was really high, like 0.5v of noise, (lol) but if your HF noise is already down below -50/60 db it's not going to do anything of value.

Put a  couple of big ferrets (SIC) on the end of your power cables if HF/Switching noise is a concern.

Alan

I really was thinking about preventing noise & such going back into the mains.

sq225917

Ferrites are your friend, all my power cables have them, my SMPS have them both ends.

uglymusic

Some of my cables have them. They seem to have dropped off over the years :-(

Alan

Ferrites are your friend, all my power cables have them, my SMPS have them both ends.

That I understand: