DAC + Headphone amp for PC

[Rufinus]

So here is my idea: i am planning to build nice quality DAC and Headamp form my PC since 95% of the time i listen to my mp3's over the headphones. I have ASUS A7N8X Deluxe mobo, which has S/PDIF out (very usefull for my Sony minidisc walkman). On other side - Sennheiser HD574 cans. As you see, nothing like top notch stuff, but enough for me. Senn's coupled with MD walkman sound pretty nice, but output from PC doesnt give even half of it, despite using ASIO plugin and drivers.

So, after some googling i arrived at this solution:

Here is the DAC: http://www.geocities.com/rjm003.geo/...o/diy_dac.html

And here is Headamp: http://headwize.com/projects/showfil...=meier_prj.htm

Now to questions part:

1) As you can see on schematics of the Headamp, it needs 15 volts. Since this project is for PC, i was wanderind how heave would be impact on quality if i use standart 12 volts from PC?
2) Same applies to DAC.
3) Since power source from PC is quite noisy, i thought that i can use filtering part from power supply for Headamp. Does it have to be redesigned somehow?
3) What about "agreement" between output of DAC and input of the Headamp?

BTW, impedance of my headphsones is 32 Ohm.
And before you tell me how noisy the environment is inside of PC, i will say that i will build entire project inside of old CD-ROM case (for shilding and mountability), plus Headamp and DAC will be placed in metal boxes which are used for EM shielding in labs and expensive gear. Connection in between will be done using 75Ohm shielded wire (something like antenna cable but not exactly) with BNC connectors.

So, now is the tima for audio guru's with constructive critics

[DC Dave]

That headphone amp uses a dual powersupply, that is +15 and -15 volts. I don't know how you would get -12 in a PC to have +12 and -12 volts. If you figure that out it could work.

I would not build it in your PC nor use you PC's powersupply for the reasons you listed. Just my .02

[richwalters]

The LM6171 isn't my favorite for headphones....too flighty....best performance I get is with circuit shown....audio noise floor down to -105dB or better (circuit not finished.. only nominal values shown) and thd at 5532 spec. The driver ic has yet to be selected and has to give low thd with low o/p Z and offest trim. Many headphone amps give high distortion at that load Z and cannot give adequate voltage swing........
My headphones have a sens of 107db/w @ 30ohms Z...rated at 1W which equals 5.5V drive voltage. If you are using bass boost this figure can be easily be reached. So dynamic headroom easily acheived with standard +/- 15V supply.
With headphones at 107dB/w sensitivity you will hear amp noise hiss at -90db down..that rules out alot of ic's....and by using paralled opamps is a good way of acheiving the drive level and low impedance required. The trick is to keep a low working impedance.

richj

[Rufinus]

Thanx for the reply, guys!

Today i reconsidered it again and found out that actually using separate transformer instead of PC power would not create inconvinience. Trafo costs 7 euro at Conrad and fits into CD box.

DC Dave, i predictet your remarc about EM noise as you see
But i'm sure that my almost triple shielding will do the job. Materials used are same as in physics research labs

richwalters, sorry, but your post i could not understand completely except that you dont like LM6171 and like idea about paralel ICs.

Author of the schematics i'm going to use, suggested also this opamps:

"Other alternatives are the LM6172/6181/6182, the OPA604/627 by Burr-Brown (used in the HeadRoom systems) or the LTC1206/1207 by Linear Technology (able to drive 30 ohm loads!)."

Whats you choice here?
And what about DAC? I also found TNT-Convertus, looks good to me too and has filtering on output stage. Here is it:
http://www.tnt-audio.com/clinica/convertus3_e.html

Well, i beleive that it can be nice project for PC enthusiasts who dont want make really overkill things but still have nice quality. And if you can combine it with LCD screen on the fronplate and some other neat things its definitely worth it .

Currently i'm designing PCB fr the amp. So, all your improvements are welcomed!

[DC Dave]

If you build it in a CDRom case withs its own powersupply you might be okay with respect to noise. If not, you can always remove it from your PC case and have it sit on your desk or put it into an external enclosure. I do feel a dedicated psu is a must, and as current demands are not great for a DAC and headamp it should not take (cost) much.

If you have more than one drive bay open, you might consider building the DAC and Headamp separately. This could make upgrading in the future easier and gives you greater flexibility.

[Rufinus]

So, DC Dave, we agree on separate power supply. First progress!

You see, that was the whole idea, to put it in CDRom case. I do have indeed 2 free bays (just because of cheap LCD screen, which fits in 1 bay easily but it's PCB needs 2 bays ). But using separate cases requires 2 cases which i dont have. Anyways, DAC and Headamp will sit in their own small metal cases (that science junk i was talking about), and small cases will be connected using BNC and shielded 75 Ohm wire (should be ok i think). And all this cases and power supply will be in CDRom case. In front of the CDRom case will be an aluminium plate which cover 2 bays. This plate will hold LCD display and headpshones connectors, switches, LED's etc..

[DC Dave]

Sounds like you have it figured out. Are you going to limit the source (music) to just the PC or are you planning on having another input to either the DAC or Headamp? You might want to plug a portable or something into the front panel to listen to. Of course available room in the case is a factor.

[Rufinus]

So, back i am to my project.

Well, i will include external input on the front panel, just in case. You never know..

And Line Out i want to make too, for my upcoming GainClone
Just got a pair of LM3875