Asrock 939dual + Spdif out mod.

[thegeek]

Hi, I've got an asrock 939dual coming in a few days, and since it does not have spdif out I began thinking
The mb uses the realtek acl850 chip(as almost,if not all, ac97-solutions do today), and by looking at the reference design and the technical documents realtek have on their website I realized that it should not be too hard to hook into the chip directly. Pin 48 is the spdifo(sp/dif out) and what I _think_ is that using this as digital coax should quite simple.
By using smd grabbers, just a copper wire, or soldering, I would think it would just be a matter of making the cable to go to your dac?

Though it is ofcourse possible that the sp/dif is deactivated in some way, it would have to have been done in hardware, as the generic realtek acl850 drivers work fine(I've read in some asrock thread).

The tech docs also talk about a "Power-off CD function" where if you disconnect the 5v from the chip, the analog(opamp) section will be disabled, and you can pass "cd output directly to speaker". Disabling the opamp section will remove any bad sonic qualities the integrated opamp has, and give you a much purer signal for your own amp.

While I doubt I'll be disconnecting the 5v pins, I will try the spdif out as soon as I get my system up and running in a few days, in the meantime; any thoughts or perhaps any brave souls that have tried this?

Tech docs and ref design:
ftp://152.104.238.194/pc/ac97/alc850...aSheet_1.4.pdf
ftp://202.65.194.18/pc/ac97/alc850/alc850_a64.zip

Generic acl850 driver for windows:
ftp://152.104.238.194/pc/ac97/alc650/WDM_A381.exe

[crodan85]

Erm I dont think it is just a case of soldering a wire on but I have had a look at the ref design and on the 4th page there are 2 or 3 circuits with some passives and an optical transmitter/reciver U3
TOTX178.



Now It looks like a connector from the TOSHIBA website but im not sure.
http://www.semicon.toshiba.co.jp/eng...77_200407.html

To be honest I might be possible if you are experienced in electronics/soldering/ but I would just buy a cheap sound card with spdif as I would find it too much hassle.

Anyway if you do decide to give it a go good luck

[thegeek]

Hmm, I don't plan on using optical, normal digital "coax" works just fine, so the whole optical transmitter-part of the circuit can be disregarded.(i hope)
I have no education whatsoever in electronics, so I'll take any advice you guys can give me, but the circuit looks really simple, do I really need the caps? Can I just use R5(100ohm)?

[crodan85]

Hmm, I don't plan on using optical, normal digital "coax" works just fine, so the whole optical transmitter-part of the circuit can be disregarded.(i hope)
I have no education whatsoever in electronics, so I'll take any advice you guys can give me, but the circuit looks really simple, do I really need the caps? Can I just use R5(100ohm)?

Well it shouldnt be to diffacult to do but you do need to use the correct passives as I might not work without . If i can find the time i will draw up a little schem for you to try but I need some sleep. Not sure how much it is going to cost and where u can get the components.

[crodan85]

Here is a quick schematic haven't worked out how it connects to the chip but I have got a rough idea. I think i have got most of the parts except the spdif connectors but i will give it a try later for you.

[thegeek]

I don't understand how your schematics are supposed to help?
They are the exact schematics you find in the reference design?
I could probably make the circuit, that's not really what I'm curious about.
I'm hoping to just use the 100ohm instead of bothering with all the parts.
Thanks anyway, but I dont see why you would bother with drawing up the exact schematic that the ref design gives you

[crodan85]

All I have done is tidy the schematic up to make it easier to read. You cannot use resistors instead of caps they do different things. I have nearly finished putting it all together and I will give it a try on my board when I am done.
Anyway I am only trying to help you It If you don't want me to bother then just say. Just out of curiosity have you got a large qty of 100ohm resistors you want to use up as you seem adamant to use them.

[thegeek]

Hehe, I don't have a large quantity of them no, but a few
I think you misunderstand a little, I'm very grateful for all/any help.
I do understand that caps are not resistors and that's not what I would like to do, I'm just wondering if the caps are really nescessary, the spdif signal from the chip should already be ok, and I wonder if all that is really needed is that single 100ohm resistor. If I'm completely wrong here please excuse me, as I've said I don't really know electronics at all
If you do try it, be careful

[crodan85]

Well, I haven't got the 100pf caps so Im going to try without them but I would say that it would effect the quality of the audio but im not sure. Well, I just have to print the chip pinnout and then Im all set to give it a go. I think I have got how it connects to the chip but for the input there may be some more components needed

[crodan85]

Right I couldn't solder the wire onto the chip as the pin spacing is far too small and there are 2 caps that make It difficult to position the wires.

I will might try again tomorrow but I don't think I can do it without removing the caps that are in the way.

[thegeek]

You really dont have to solder. Take a stranded copper wire, and remove _one_ strand. Take this one strand and put it around the pin and "twist it around" until it is firmly in place(please excuse my poor attempt at explaining, english is not my first language). Then use some hotglue or anything else that works to keep it in place. Then solder a larger wire onto this single strand(perhaps do this first).

As for the quality of the audio, remember this is a digital signal, and the only thing that can affect it is massive noise or jitter. I don't think noise will be a huge issue, even without the filtering caps and jitter is not something you should be concerned about, considering we are talking about a ac97 chip here, not some high-end dac
The only thing I _think_/hope is important is the 100ohm resistor... (pure speculation from an idiot:P)

Hopefully I'll get my board in a day or two, and as soon as I get my system up I'll try it myself.

[crodan85]

The chip is just over half the size of my finger I don't think there are smt grabbers that fit the pin spacing. I have managed to get some smaller wire but Im waiting on some solder braid to remove 2 caps that are in the way of the two pins that i need to solder. I have tried using a solder pump but there is some sort of coating on the leads making it hard for the solder melt properly

Just in case anyone is curious I have got some pics of the board and similar size chips to show how it isn't really practical to glue wires on

http://img.techpowerup.org/060109/caps.jpg Pic of the caps that are in the way

http://img.techpowerup.org/060109/DSCF1930.jpg pic of a similar size chip (must excuse my big finger )

http://img.techpowerup.org/060109/DSCF1934.jpg Pic of the pcb

Anyway I wont be able to try again until i get some solder braid hopefully tomorrow but as soon as I do i will give it another go.

If you do decide to give it a go with solder be careful

[thegeek]

Hehe, I never intended to use solder
Do you think it would work with just using a single copper strand?

[crodan85]

Well i wish u all the luck trying without. I am using an old ide cable for wire. I did try using CAT5 cable but it proved to be too big

[thegeek]

Cat5 would be too big yes, because it is a solid core wire, you need a stranded wire, (lots of many small wires). A wire from an ide cable would probably works just as well yes

[persivore]

The capacitors are probably to provide some sort of filtering for the signal. The 100ohm resistor could be some sort of current limit incase the output gets shorted to ground.
Without the capacitors in place, you might get very distorted sound (or possibly no sound at all as the signal is digital).

If you are having problems soldering to the leg on the chip, try using some enameled copper wire. You should be able to get some which is easily thin enough to connect to the chip

[Revv23]

does the chip go to the underside? maybe you can solder it on from the bottom, though persivore has a good point.. though i dont know that much about digital stuff, im wondering if that sort of signal would need any filtering... ive noticed that in digital gear the quality of the cable i use matter much less then with older analog stuff... so maybe those caps are the just for that, the analog outputs.

[thegeek]

Though the filtering is probably nice to have in a ref.design I doubt it is really needed, hence my earlier questions/posts.
I got my board last night and as far as I can see it should be entirely possible to get a small wire around the pin. It might also be possible to just solder onto one of the resitor/pads around the chip, but I'll have to check that out more closely later.

[thegeek]

Update:

I did both the vmod and the spdif mod today. Vmod worked great. As for the spdif mod; as far as I can tell I soldered to pin48 perfectly. However, after taking a look at the realtek drivers it seems that the driver somehow detects that spdif is not "enabled" on this board. This in turn means that the control panel won't even show the spdif/digital tabs. I suspect alcxwdm.sys has to be modified to enable spdif, I might do this but at the moment it's just not worth the effort
If anyone wants to take a look, ida works just fine, but unless you are really good with a kernel-mode debugger you'll need to reboot every time you make a change in order for the system to reload the driver.
There's lots of clues to start from so if anyone tries it; good luck

[crodan85]

thegeek check the datasheet there is an input and output pins. Pin 47 is spdif in and 48 is spdif out. Just out of curiosoty did you solder or use another method.

[thegeek]

First off, I know very well that there are two pins, 47 for input and 48 for output. I'd think that was obvious from the beginning. As I said I first tried without soldering but that was annoyingly flimsy, and I was worried that the connection might not be good enough, so I soldered direcly to the pin(48).

[crodan85]

Ok but have you tried both pins at the same time with the schematic in the ref design. Without following the ref design Im not really surprised that it doesn't work. Until someone tries the full schematic for the input/output there is no way to find out whether it works or not. I know what you mean by fiddly I can get one wire soldered but when trying the second I always end up bridging the two pins together.

[thegeek]

There is no point to messing with them both at the same time, as for the full schematic, you might be right. However, unless we can hack the drivers to enable spdif it won't matter. It seems the drivers actually check something(chipset?, the ali audio controller?) and only enable spdif where is is available. This means that even if we had the hardware 100% it won't matter because the drivers won't allow us to use the digital parts at all.
I found it fiddly to _not_ solder, though the pins are small the soldering is not the problem at all.

[PMM]

It maybe that indeed you need to make a partial ground for it to work.

I.e. the chip may expect.. part of that addition circuit in the sense that
the effect of it tells the chip its in place.

other parts of the chip bit like PWM for controlling CPU voltage
maybe monitoring voltage / current.

I agree in the sense that the cap's are just filters but that extra 220Ohm
resistor might need to be included after your 100ohm current limiter.

[joeyjoeyjoey]

Sorry to bump an old thread but I actually registered because I found this thread on a google search. Has anyone gotten this to work? I know pin 48 is the s/pdif out but as far as the digital ground of pin 4 or 7 I just dont know which one to use. Or does it just need a chassis ground to work?

Any help would be great.