Transformer Size for a Dedicated Audio Computer?

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Transformer Size for a Dedicated Audio Computer?

Postposted on Thu Nov 21, 2013 11:58 am

Hey, friends and future friends. :)

I'm working on a DIY project building balanced power conditioners with a group. We can pick one or two transformers, and pick the size of each. Someone strongly recommended I use two transformers since I'll likely be using a computer as a source, and it's best to keep that separate. I believe the options for transformer sizes are 100VA, 300VA, 600VA, 800VA, 1000VA, and 1500VA. Bigger ones cost more, of course.

If I go the route of a laptop, what size transformer do you recommend I go for?

And if I go the route of a dedicated audio computer, what size transformer should I get for it? Perhaps something modest, like a low power Haswell CPU, integrated graphics, and one HDD or SSD.



And while I'm here, any advice for parts for a dedicated audio computer? Or OS recommendations?
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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Thu Nov 21, 2013 2:33 pm

Check the power factor on the transformer, if it's say 0.7, then 1000kVA will be good for about 700W.
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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Thu Nov 21, 2013 2:43 pm

Once I find that out, how many watts should I need to reserve for a low-powered desktop? Or a medium laptop? Or a NUC?

Do we know if there will be desktops available with Bay Trail or Cherry Trail?
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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Thu Nov 21, 2013 8:32 pm

jihadjoe wrote:Check the power factor on the transformer, if it's say 0.7, then 1000kVA will be good for about 700W.


No. Transformers are rated in VA. If the load on the transformer has, say, a 0.7 lagging PF and consumes 700W of real input power, it's supplying 1000VA of apparent power. The same transformer could supply 1000W at unity PF.

Transformers don't have a power factor like a motor does. Due to internal impedances, they do contribute to the overall power factor which must be supplied from the source side, but that effect is very much dependent upon the current being carried across a tranformer's windings.

Transformer's are always sized to provide a target operational lifetime for the anticipated load it will have across it's secondary windings. The higher the load, the more losses there will be heating the coils on the transformer. The more the coils are heated, the shorter the lifetime of the transformer. Most commercial dry-type transformers can deliver 200% of rated current for brief periods, and lesser overloads for longer periods (dependent on ambient temperature, as well).
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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Thu Nov 21, 2013 9:18 pm

jihadjoe wrote:Check the power factor on the transformer, if it's say 0.7, then 1000kVA will be good for about 700W.

I think you mean 1000VA rather than 1000kVA :o . But as bigfoot said, you rate the transformer for it's output load at unity. And any PC or laptop built in the last 10 years will have PFC in the supply, so unity can be safely assumed.
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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Thu Nov 21, 2013 9:29 pm

Milo Burke wrote:Hey, friends and future friends. :)

I'm working on a DIY project building balanced power conditioners with a group. We can pick one or two transformers, and pick the size of each. Someone strongly recommended I use two transformers since I'll likely be using a computer as a source, and it's best to keep that separate. I believe the options for transformer sizes are 100VA, 300VA, 600VA, 800VA, 1000VA, and 1500VA. Bigger ones cost more, of course.

If I go the route of a laptop, what size transformer do you recommend I go for?

If there's a laptop out there that needs 600VA I'm not sure I could afford it. Nor would I want to. A 300VA unit should be plenty. Same for the desktop unit. Are you planning on isolating your displays? You might want to confirm that you can float the computer while it's tied to the displays chassis ground over DVI/HDMI.
This problem was caused by Windows, which was created by Microsoft Corporation.
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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Thu Nov 21, 2013 11:48 pm

Low-powered laptop audio computer?

Okay, you don't need the fastest i7 on the planet for a decent audio computer these days, but "low powered?"

I don't get what you are trying to do. Not at all. Please define the terminology. What do you mean by "low powered" and what do you mean by "audio computer"?
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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Fri Nov 22, 2013 11:44 am

I appreciate the replies!

One definition of low-powered is to get the lightest Haswell i3, use integrated graphics, and generally not laden the computer with performance parts. Run a modern OS on it, then only use it to run a media player. Doesn't have a lot of performance, doesn't need it. Doesn't use a lot of electricity either.

If I go with this option, I'll probably get a smallish low-res monitor to put on the floor completely out of the way from speaker-to-ear interaction. All I need to do is run a media player with a wireless keyboard with a trackpad.

Another definition of low power is to get a NUC with an Atom (hopefully one with the Bay Trail refresh in it?) and install an audio-based OS on it. I just found about Daphile yesterday, for example. 200 MB ISO, headless, geared towards 1-2GB RAM, plays back crazy high sample rate music, etc. The website isn't clear on this, but I believe it is controlled through apps on smartphones or tablets. But it doesn't mention which apps are compatible or where to get them?

Clearly I don't need much performance, so I could use something like an 8 year old desktop. But that would use heaps of electricity and have lots of noisy fans. If I'm going very low performance, maybe I could get something cheap and fanless.
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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Fri Nov 22, 2013 12:00 pm

I forgot to define audio computer. I'm just looking for something dedicated, with no other programs installed, that can host a media player to manage and play back my music. And send it to an external DAC.

I've got a pretty knowledgeable friend that swears by Macs for this purpose. He suggested I get a used Mac Mini. I hate Macs. :oops:

I believe bit-perfect playback through Windows (bypassing all the internal volume mixers and sample rate converters) is possible, but more difficult than other OS's. It should be easier without multiple programs vying for control of the DAC, and with virtually every Windows service turned off. I'm a Windows guy myself, but I've never had a dedicated computer for audio before.

I don't know how easy it is to get a decent media player and bit-perfect audio output on Linux. Never used it.

And one of these dedicated audio-streaming OS's like Daphile intrigue me.
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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Fri Nov 22, 2013 1:03 pm

Milo Burke wrote:I forgot to define audio computer. I'm just looking for something dedicated, with no other programs installed, that can host a media player to manage and play back my music. And send it to an external DAC.


Then you don't need any power conditioning on the computer at all as the computer is only involved in the digital side of things. To be fair, even it your were allowing the computer to do the final analog conversion, a power conditioner is not going to help in the least with noise on the signal coming out of the computer. Any noise that managed to make it through the switching supply of a computer and into the audio output lines on a sound card are going to make it through a power conditioner too and are likely going to do damage.

The noise on analog signals coming out of a computer are going to be generated internal to the computer, not externally.

If you are really that paranoid, find a computer with an optical digital output and run it to a separate DAC that is on conditioned power and such. But make sure you get audiophile grade digital power cables, otherwise you'll likely still end up with noise in the system.

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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Fri Nov 22, 2013 1:14 pm

Good gravy, I'm not going to get power cables like that. My opinion is that they're all marketing hype. I trust those guys as far as I'd trust a used car salesman.

The suggestion of running the computer through the power conditioner was only from one person. Maybe that's the broader question I should find a question to first.

My current DAC has USB, coaxial, and optical inputs. I suppose I'll be using USB if I'm using a minimalist computer.
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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Sat Nov 23, 2013 11:59 am

Milo Burke wrote:Good gravy, I'm not going to get power cables like that. My opinion is that they're all marketing hype. I trust those guys as far as I'd trust a used car salesman.

The suggestion of running the computer through the power conditioner was only from one person. Maybe that's the broader question I should find a question to first.

My current DAC has USB, coaxial, and optical inputs. I suppose I'll be using USB if I'm using a minimalist computer.


If you use USB, then you are at the mercy of the DAC designer as to whether you get noise from the computer. If there is good digital/analog isolation and good design techniques then your likely fine from that perspective. If you have unbalance outputs on the DAC, you will be sharing the same ground as the computer though and you can get ground loops and the associated 60hz hum. That would be my main reason for saying to use optical for the computer to DAC connection.

In reality, you obviously have a computer now and if you have the DAC, give it a try. If you don't get hum, don't worry about it. Same with noise in general. Plug the DAC into the computer and your amp and turn your amp volume way up with nothing playing. Now do unmusic related thing on your computer. Do you hear any noise? If the answer is no, then you have nothing to worry about. If you do, unplug the DAC and the computer and see if you still hear noise.

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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Sat Nov 23, 2013 12:20 pm

sluggo wrote:
jihadjoe wrote:Check the power factor on the transformer, if it's say 0.7, then 1000kVA will be good for about 700W.

I think you mean 1000VA rather than 1000kVA :o . But as bigfoot said, you rate the transformer for it's output load at unity. And any PC or laptop built in the last 10 years will have PFC in the supply, so unity can be safely assumed.


Good catch. Although I think a transformer in the MVA range would be more than up to the task... :-?
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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Sat Nov 23, 2013 12:33 pm

lulz at my own post. 1000kVA indeed :o
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Re: Transformer Size for a Dedicated Audio Computer?

Postposted on Sat Nov 23, 2013 1:09 pm

Milo Burke wrote:Good gravy, I'm not going to get power cables like that. My opinion is that they're all marketing hype. I trust those guys as far as I'd trust a used car salesman.

SecretSquirrel was being facetious.

Milo Burke wrote:The suggestion of running the computer through the power conditioner was only from one person. Maybe that's the broader question I should find a question to first.

As already noted, since you're planning to use outboard DACs, power conditioning for the computer (especially for a laptop, which effectively has its own built-in UPS) is pointless.

I'd also like to point out that worrying about minutiae like this is not worth the trouble unless you're planning to play high quality source material (i.e. no lossy compression). If you're just going to play MP3s on it even the outboard DAC is of questionable value.
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