Asus Xonar DX Mods!

[rds]

I wasn't able to find a mods thread for this card anywhere and this card can be really nice with a few basic mods. So I've taken some time to figure out what is what on this card in terms of the stereo output stage.

Note: Everything on this card is surface mount and the board is very cheap. This requires some soldering skills if you want to be able to use the card again

I don't think this is good beginner project.

Mod 1: Quality coupling caps

I chose to go with 22uF (same value as stock/CS4398 datasheet) 25V Nichicon Muse ES bypassed with 0.22uF Wima mkp.
[FYI All the stock electrolytic caps appear to be 10V.]

These are the left and right front coupling caps:




Twist those back and forth (gently) until they break off. Throw out the garbage on there so you're left with just the solder pads.
I should say now, keep your soldering iron on low temp. I used 250C - this is as high as you should go.
Add a little solder to the pads.
Add the caps of your choice.
Notice here I have the leads bent at a 90 degree angle to easily solder to the pads. One of the Muse leads is not soldered so you can see what I'm talking about.



I choose to use Wimas in parallel with the Muse.

Mod 2: Quality High Pass Caps

I'll admit I'm not totally sure how this is working. It appears to be a high pass filter that is in series with output caps (low pass filter).
This is not as significant as Mod 1.
I used the same method to replace the integrator caps (the only other caps in the signal path [yes there are film caps on the integrator but they are in parallel with resistors or to ground]). I used 220 uF (same value as stock) 25V Nichicon Muse KZ.



Mod 3: Upgrade Op-amp (yikes!)

Note: There may be a second opamp before the output. I doubt there is, but it is possible. The opamp I have circled is definitely the cs4398 DAC opamp, but I haven't gone through the painstaking process of determining whether there is another opamp before the output. ...if someone wants to...

Now I also decided to replace the opamp. You should think twice and maybe even three times about this. Maybe listen to the card first - It sounds pretty sweet at this point. If you've never done something like this you'll probably lose your card :/



I decided to replace it with a dip 8 socket on the other side of the board.
You can see that in the previous picture.

It sounds a lot better now. Very detailed and clean

I've also added better power filter caps and decoupling caps for the opamp

To my surprise the wires for the dip 8 socket aren't picking up any noise.

[m0b1liz3]

Yeah, I was thinking of replacing the opamp on my line 6 guitarport. I am holding off for the time being since I have realized my soldering will improve more if I do a few other projects first.

[Maniac]

Let me provide a bit of info on the SMD SOIC (that's what they call the package of those SMD op-amps) desoldering that I've learned on my previous employment.

First of all, you put a large blob of solder on the more crowded side of op-amp's legs (for example, on the photo above, you'd be putting the solder down on the left first). After you made a large blob that covers all 4 legs of the op amp, you then proceed to do the same to the other side.

When you saturate the second side with solder, quickly move on to the previous "blob" and quickly melts it while the other blob is still liquid. when you find it melts, you flick it lightly and the whole thing, including most of the solder will fly off the board.


If it didn't work the first time, go back and heat up solder on the empty side (on the photo above, it would be the right side), then quickly go to the other side and flick it off toward the empty side when you melts the solder on the other side.



Of course, make sure you flick it in a direction where there's no components in the way, or you'd have quite a mess to clean up. And as always, practice it on stuff that you can afford to damage and destroy before moving on to the actual stuff.

After the removal, just use solder wick to quickly mop up the excess solder and you'd be ready to put a new op-amp in.


I usually use a 30W soldering iron for 63/37 leaded solder, and 40W soldering iron for the newer unleaded/RoHS/Green solder.



For anyone who just want the most important tip, BE QUICK. If you are good with this technique, it would actually be less stressful to the pads than desoldering it one pin at a time. (takes about 30 secs on average to do the whole process...)

[rds]

That's some really good advice - thanks Maniac!

[rokk]

I've been trying to check which opamp was used for the front channels.
How did you manage to find out which op that was used?

Thanks alot, also, which opamp replacement did you use?

[rds]

How did you manage to find out which op that was used?

With a multimeter and the cs4398 datasheet.

Thanks alot, also, which opamp replacement did you use?

I first tried the ad8620, but found that the sound was too harsh. Now I'm using the opa2132, and it sounds good
But YMMV, it really depends on the rest of your system I guess.

EDIT: I'm back to the ad8620 and I'm liking it

[rokk]

Thank you for figuring it out of me, I don't own an multimeter anymore so it was a hassle to borrow one. Was planning on doing what you did but never came to it. Thank you!

I have an LM4562 waiting to be put on the board, i also have some AD-amps i might try, and of course an 2134 as well.

I also have some Cerafine capacitors that might work?

[rds]

Sounds like you're ready to go with this. Cerafines should be very nice.

[rokk]

Changed the opamp in 10 mins, it was a no-brainer.
The way I did it with the cheap opamp on the card is a bit more crude.. I just cut the legs off and removed them from the pads with the soldertip. Then I just put the new LM4562 SO-8 in it's place and soldered it there.

Sounds.. different, more dynamics in the music, more silence yet the details are mostly preserved. Something happened to the vocals too, the music seems calmer and the bass has more definition.

Maybe time to play with the caps?

[rds]

Cool, it's good to hear back from someone else trying this.
Definitely try swapping out the coupling caps (Mod 1). It's easier than the opamp.

Another mod I found to be significant was adding more and better capacitance to the decoupling/power rail caps.
I'll add that in later. Also very simple.