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Old 13th March 2014, 05:13 AM   #1
BonkM is offline BonkM  Canada
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Default Building a linear ATX PSU for an audio PC. Need help & advice

Hey guys,

This needs a bit of explaining and there's a few questions. I'll lay it all out and then give a final #'d recap of what I need help with.

So,

I currently use a 550w FANLESS Seasonic ATX PSU for an audio only PC that I've got. It's fine, but I'd like to have a go at making my own linear PSU to feed all the rails of the PC.

I know there may not be much proof on the topic, but hopefully a linear PSU makes a difference to the sound. I'm going to try, so keep that in mind.

Info on my PC:
*The audio PC is just a transport outputting the music data via USB to my stand alone DAC. There's no soundcard or Digital to Analog conversion going on inside the PC.

Parts:
standard mATX Gigabyte G1 Sniper M5 motherboard,
i5 4670k CPU (underclocked to 1.6Ghz),
16GB (4x 4Gb 2100mHz underclocked to 800mHz),
1 Corsair 128Gb SSD,
and 2 PCIe cards (1 is a USB 3.0 card that needs to be able to supply up to 3A to it's peripherals, and then 1 expansion card that takes almost no power).

So no big power eaters, and I'd say total we're looking at ~60-90w. I haven't tested this myself though, just guessing from the components.



The few full ATX linear PSUs that are out there cost at a minimum $1700USD from TeraDaks and go up to $3000/5000 for a Paul Hynes one. Both too far gone on my personal cost to benefit ratio.

I'm not 100% sure of what rails the PC needs since this is my first kick at the can, but from what I've found I'll need to supply +12v, -12v, +5v, -5v, +3.3v, and a special +1.65v for a dedicated RAM PSU.
Is that correct?

As for current, though the PC isn't going to be using much power, I'd like to have a good supply on hand just in case I reuse it for something else in the future. So I'm looking at something like the Seasonic's 500-600w.

As for how, I was thinking to use AMB's Sigma 11 Linear PSU boards + toroidals for the single rails, and the Sigma 22 for the +/- rails. These PSUs are proven work horses and have super low ripple. This part of the build should be pretty straight forward, selecting voltages and then spec'ing the boards+toroidals to output it. However, how many toroidals and what size (voltage and physical) will I need to supply those boards?

One other problem I have is with getting the PC to start. From what I've read the ATX PSUs don't just simply go from either "off" to "on". There is a sequence that the rails need to go live in, and since I've got a dual-bios motherboard, one of the 5v lines actually goes off and on twice.
- So, what I need to make or scavenge is some kind of switch that will start up my DIY PSU in the same order so that the result is just 'push button' :-D

Recap:
1. What are the necessary rails that an ATX PSU needs to supply?
- and keep in mind that I need a dedicated 1.65v rail to supply the RAM.
2. How many toroidals, and of what size (voltage and physical), will I need to supply power to the various rails?
3. Where can I find, design, or make a switch/logic board to correctly supply the timing sequence of the rails during power on/off?
- I want to just connect the looms (24pin, 8pin, 4pin) and then use my DIY PSU with my audio PC as if it were a standard ATX one. Some quirks, sure, but nothing about opening the lid or pulling cables.

Thanks a lot, guys. That's it for the first volley, and I'm sure I'll have more as the project moves ahead.

Last edited by BonkM; 14th March 2014 at 06:43 AM. Reason: more system info.
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Old 13th March 2014, 08:03 AM   #2
lexer98 is offline lexer98  Argentina
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Seasonic make greats PSU with very low levels of ripple and efficient DC-DC desings .... I think is unnecesary build a DIY PSU, is really hard and you are missing a lot of stuff ....
I had problems too with electronic noise on my sound card, generated by the Videocards and hard-drives, solve it by adding capacitors on the card and changing filter capacitors of the PSU for a better ones.

Click the image to open in full size.

Last edited by lexer98; 13th March 2014 at 08:05 AM.
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Old 13th March 2014, 11:59 AM   #3
DUG is offline DUG  Canada
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Quote:
Originally Posted by BonkM View Post
Hey guys,

...

I'm not 100% sure of what rails the PC needs since this is my first kick at the can, but from what I've found I'll need to supply +12v, -12v, +5v, -5v, +3.3v, and a special +1.65v for a dedicated RAM PSU.
Is that correct?

As for current, ...

Look at the current rating of the ATX supply you are now using.

3.3V at how many amps?

5V at how many amps?

There is a reason it is a SMPS.

As for noise from the SMPS: What frequency is the SMPS?

Are you saying that you can hear that frequency?

Does even 50mV of ripple on a 5V digital line cause the digital signal to be different?

IMHO the first place you should direct your energies would be the power supply to the sound card.

This is where analog is generated.

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Old 14th March 2014, 06:39 AM   #4
BonkM is offline BonkM  Canada
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Thanks for the 2 responses, guys. Being into audio and DIY, I know that some things don't make a difference in the end, but that part of the point is the journey. I WANT to make a linear PSU for my PC and I HOPE that it sounds better. I don't WANT it to sound better and HOPE that I can make one. Know what I mean?

@ lexer98 - I don't specifically have a noise issue, I just hope to make it better. I also don't have any spinning anything in the PC. No fans, HDDs, disk drive, or fan on the PSU. So nothing to cut down on there. I do agree about putting capacitors on the rails, which I will be doing, but didn't want to get sidetracked on in this thread.

@ lexer98 - You also said I'm missing lots of stuff, like what? I'm all ears, so anything you can tell me is great.

@ DUG - What do you mean by "look at the current supply, there's a reason it's SMPS"? Are you trying to get me to notice that it's really high? If so, yes, I'm aware that the benefit of SMPSs is their high output current. And a downside to LPSs is their lack of current. That's why I need help in finding out what to do to get there.

The other thing is that I don't have a sound card. The PC is just a transport that outputs the music data via USB to my DAC.
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Old 14th March 2014, 01:06 PM   #5
DUG is offline DUG  Canada
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Quote:
Originally Posted by BonkM View Post

...

@ DUG - What do you mean by "look at the current supply, there's a reason it's SMPS"? Are you trying to get me to notice that it's really high? If so, yes, I'm aware that the benefit of SMPSs is their high output current. And a downside to LPSs is their lack of current. That's why I need help in finding out what to do to get there.

The other thing is that I don't have a sound card. The PC is just a transport that outputs the music data via USB to my DAC.
OK.

Look up high current low voltage linear regulators and that will point you in the right direction.

You will need high current low voltage transformers and some good rectifiers.

There is a stand alone synchronous rectifier controller IC that controls four FET's in a bridge rectifier application...I designed a board for it but can't find the part number (or where my files are). I don't know how low in supply it will go but it will really help with efficiency of high current supplies.

If you go too high in filter cap capacitance in an attempt to reduce ripple voltage beware of high peak currents in the transformer/rectifier path.

Use a star ground when connecting all of the supplies together. This will also be the exit point for all supplies.

Happy learning.



ps external DAC...good
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Old 14th March 2014, 03:15 PM   #6
BonkM is offline BonkM  Canada
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Quote:
Originally Posted by DUG View Post
OK.

Look up high current low voltage linear regulators and that will point you in the right direction.

You will need high current low voltage transformers and some good rectifiers.

There is a stand alone synchronous rectifier controller IC that controls four FET's in a bridge rectifier application...I designed a board for it but can't find the part number (or where my files are). I don't know how low in supply it will go but it will really help with efficiency of high current supplies.

If you go too high in filter cap capacitance in an attempt to reduce ripple voltage beware of high peak currents in the transformer/rectifier path.

Use a star ground when connecting all of the supplies together. This will also be the exit point for all supplies.

Happy learning.



ps external DAC...good
Thanks :-) I'm a big fan of the external DACs. I'm on my 3rd one now, a PS Audio PerfectWave Dac Mkii, after slowly moving up the scale. I'll be sticking with it for the foreseeable future, I'm very happy with it. It's partly why I've started my new journey to upgrade the parts that come before it to hopefully supply it with the best signal possible.

As for the other things, thanks. I was actually hoping to use the AMB Sigma 11(single rail) or 22(dual rail) kits because they side step me having to learn about regulating the unregulated toroidals that I'll be needing.

The Sigma 11/22 is capable of being configured in almost any output under 36V, and I'll be needing nothing near there. As for current handling, their MOSFETs are rated at 18A, but I'll be shooting for ~10A for the 12V rail and less than that for the rest. In saying that, those are different ways of tackling exactly what you mentioned, right?

The star ground is a good tip and I'll have to keep it in mind. I only drawn out a general schematic of what I want to do, but haven't looked at grounding anything yet.
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Old 15th March 2014, 01:07 AM   #7
lexer98 is offline lexer98  Argentina
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Sorry for the offtopic
Computer PSU have only 5 rails .... 5V , 3.3V , 12V , -12V and 5vsb.
5V, 3.3V and 12V ... power up the most parts of the computers (CPU, RAM, Chipset ect...) in modern computers the 12V rail is to become more important beacause supplying all devices that consume more energy as the CPU and graphics card. High-end PSU (>1000W) uses a DC-DC desing what means have a chopper transformer with only one winding which delivers .. 100A @ 12v or something like this, the rest of the voltajes are generated with regulators
-12V .. for the devices what need simetrical power supply , like onboard audio ... very low current no more than 1A
5vsb - that is the standby rail ... usually power up the USB and some other devices like ethernet ... arround 3.5A
All of the rest of the voltages like CPU , RAM ect ... are generated by a PWM Controler and mosfet in the motherboard.

You need to bypass two signal to get working the computer with your DIY PSU:

>"power good signal" grey cable that signal is generated by the monitor IC of the PSU, is a 5V signal with is measure by the motherboard ... if the signal lasts less than 500ms means that the PSU is OK ( Temperature, voltajes, current ect ...)
Click the image to open in full size.

>PS_ON the green cable .. 5v is a signal that the motherboard connected to the GND when you push the POWER UP BUTTON and turns on the PSU

But you can remove a IC monitor chip from a cheapo PSU and use it or buy one

Example: http://www.fairchildsemi.com/ds/FA/FAN7680.pdf.



Read the ATX specifications for more information : http://www.formfactors.org/developer...s%5Catx2_2.pdf

Good luck with your project

Last edited by lexer98; 15th March 2014 at 01:33 AM.
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Old 20th March 2014, 06:59 PM   #8
BonkM is offline BonkM  Canada
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Alright, I've mostly got that stuff now. I also read up on 2 other super helpful links on getting an LPS powered mobo to post that were on Audio Asylum. From what I gathered, both routes are looking at an external switch for the 5V POWER_OK line. THe idea seems to work, but I'm REALLY looking to find an internal way for that.

There MUST be something out there that can mimic the necessary timing for that so that I can make a "push button" solution for this full power supply.

Secondly, what toroidal transformers do you guys recommend? I guess that I'll need a 12V @ ~+10A for the 12V and 5V rails, and then a smaller toroidal for the 3.3V and 1.65V rails. I have no idea where to buy from or what ones would be good/sound good here. Advice greatly appreciated.
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Old 24th March 2014, 07:48 PM   #9
lexer98 is offline lexer98  Argentina
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Quote:
Originally Posted by BonkM View Post
Alright, I've mostly got that stuff now. I also read up on 2 other super helpful links on getting an LPS powered mobo to post that were on Audio Asylum. From what I gathered, both routes are looking at an external switch for the 5V POWER_OK line. THe idea seems to work, but I'm REALLY looking to find an internal way for that.

There MUST be something out there that can mimic the necessary timing for that so that I can make a "push button" solution for this full power supply.

Secondly, what toroidal transformers do you guys recommend? I guess that I'll need a 12V @ ~+10A for the 12V and 5V rails, and then a smaller toroidal for the 3.3V and 1.65V rails. I have no idea where to buy from or what ones would be good/sound good here. Advice greatly appreciated.
10A is too little for your computer ... minimum a 12V @ 25A transformer and computers PSU don't have 1.65V rail that is generated by the MB

Simple solution is buying a Pico-ITX power supply ... something likes this 250W M4-ATX Smart Power Supply for Carputers ... and feed it with your lineal power supply
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Old 24th March 2014, 08:04 PM   #10
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Quote:
Originally Posted by lexer98 View Post
Simple solution is buying a Pico-ITX power supply ... something likes this 250W M4-ATX Smart Power Supply for Carputers ... and feed it with your lineal power supply

It is not a good sounding solution at all. Something similar to the Pico (Nano) prompted me to build a linear supply. Admittedly, for a very low power i3, but it made a very substantial difference soundwise. There was a thread about it somewhere...
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