[S_Dedalus]

Well, I finished modding my 0404. THe output caps are gone, as are the buffer opamps, and the output opamp has been swapped for an LT1364.
Each step in the process brought improvements and interesting changes to the sound, and the possibilities are pretty much endless depending on your card, what you are willing to spend, and the sound you are going for.
The first mod I did was to bypass the output caps, and then check the card for DC offset. Luckily I got a card with very little offset(<1mV), so the caps came off. This was almost like going from the av710 to the 0404, as everything became more transparent, and you could tell by the RMAA results as well as listening. There is a slight peak in the highs, which I think accounts for the card's more forward nature.
The next mod was to either remove or replace the buffer opamps. I decided to remove them, mainly since I didn't want to spend $25 to upgrade the chips on an $80 card. In order to remove them and still get sound, just bridge the input pads to the ouput pads. I think the stock opamps have got to be slow or something, because everything tightened up, especially the bass, and instrument separation really improved, and thus the soundstaging improved. It's not a huge jump, but it is noticeable.
Be very careful when removing the smd parts, I wasn't, and I ripped one of the traces off. Luckily I was able to find a way to wire it back together, but you don't want to try it, trust me.
The last mod was to replace the output opamp. This time I was much more careful, and it came off with no problems at all. Plugging the new chip in was a snap.
At first when I listened, I thought, where did all the bass go? All was well, however, when I realized that it wasn't a lack of bass, but a re-imagining of it. Midbass is a whole lot more controlled now, very fast, very punchy, and the low bass, well with the DT770's, you can be hearing nothing at all, but your entire skull can be vibrating, this actually fits with the RMAA results, because according to them, the bass really only starts to roll off around 10hz.
In the end, I'm very happy with the results, and the mods really only cost me $6. However your mileage may vary, as not all cards will have low offset, and then you'll have to play with output caps, which will really drive the price up in order to get results similar to having no caps at all.
I'll post pictures, and comparisons later on, pictures sometime tomorrow, and comparisons after the Champaigne meet.

 

[gaboo]

Nice work. Is a picture too much to ask for?

I wonder why 0404 had buffer op amps. There are none on 1212m 0202 (analog) board. There is a inverting a non-inverting output op amp on each channel.

 

[S_Dedalus]

Well, untill I go buy some AA's, a picture won't be forthcoming, but that should only be till tomorrow sometime.
The 0404 has unbalanced outputs so it only needs one dual opamp, and I'm not sure why it has buffers, maybe the output from the dac isn't as strong as the 1212's.
How do I put up the RMAA results? the max attachment size is half what I need, and I don't have any way to host it.
Since I don't know how, and people might want to know the results before I can post the full report, here's the summary.

Frequency response (from 40 Hz to 15 kHz), dB: +0.10, -0.02 Excellent
Noise level, dB (A): -112.7 Excellent
Dynamic range, dB (A): 112.1 Excellent
THD, %: 0.0024 Excellent
IMD, %: 0.0024 Excellent
Stereo crosstalk, dB: -109.5 Excellent

 

[lan]

If you have webspace, you can upload the RMAA results.

DO you have pre and post mod RMAA results?

 

[S_Dedalus]

I don't have any way to host them myself, as my webhost is really bad, and I can no longer access my site.
The pre-mod results were much closer to your 0404 results, but there was a bit more bass rolloff, I think it was -.06 dB., and there was a hump at 60hz in the dynamic range, noise, and THD tests which is gone now.

 

[dreamnid]

You can try re-compressing the pictures and hopefully the quality will be legible enough to read.

 

[mikechai]

Quote:

Originally Posted by S_Dedalus In the end, I'm very happy with the results, and the mods really only cost me $6.

I can't believe it. Only $6? That seems well worth it.

 

[Vosper]

What are the stock op-amps?

 

[S_Dedalus]

Would anyone care to host the results? I can't get it under 40KB while still being legible.
EDIT: The opamps are all JRC 2068

 

[S_Dedalus]

Donovansmith was kind enough to host it, so here goes.
http://hosted.donovansmith.us/~s_dedalus/

 

[S_Dedalus]

If anyone wants to try this, I got two LT1364's in case I fried one while soldering it, obviously the first survived, so I have a surplus unit.

 

[Glassman]

nice work Dedalus, forgot about that CRD stuff, huh?

with the buffer opamps in place the card measures slightly better in THD and IMD.. (0.0020% instead of 0.0024%) but.. as the opamps are just a unity gain non-inverting amps w/o any low pass network and are being fed with HF garbage from delta sigma DAC I believe this is the answer to why it sounds better w/o them.. and of course the less active parts in signal path, the better..

you shouldn't worry about output offset, it's way more dependant on the opamp used than on the DAC chip onboard.. really no problem there, even if it was 10mV which is not likely to ever happen..

 

[S_Dedalus]

Quote:

Originally Posted by Glassman nice work Dedalus, forgot about that CRD stuff, huh? with the buffer opamps in place the card measures slightly better in THD and IMD.. (0.0020% instead of 0.0024%) but.. as the opamps are just a unity gain non-inverting amps w/o any low pass network and are being fed with HF garbage from delta sigma DAC I believe this is the answer to why it sounds better w/o them.. and of course the less active parts in signal path, the better.. you shouldn't worry about output offset, it's way more dependant on the opamp used than on the DAC chip onboard.. really no problem there, even if it was 10mV which is not likely to ever happen..

I didn't forget, I'm just not that confident in my soldering abilities. I'll probably do it when I order parts for my next amp project.
Also, the opamps are pretty crappy.
I'm inclined to advocate paranoid levels of testing after frying my first pair of good headphones.

 

[Glassman]

whawhawhawhat do you say?? :-0

 

[S_Dedalus]

Quote:

Originally Posted by Glassman whawhawhawhat do you say?? :-0

Yes, I did consider biasing the lt1364 into class A, but I'm not quite confident in my soldering abilities, I'll build another amp, and then try it.

With regard to the 0404 sounding better without the buffer opamps, its not just that they are in the signal path, its also that the stock opamps are pretty crappy.

And the last one is about the offset voltage being very low on the card, I'm just paranoid, because I fried my headphones without testing properly, so now I test everything no matter how silly.
I hope that clears things up. I should probably go to sleep and post when I'm not so incoherent.