[nutrax]

Okay! I finally gave in to the temptation and modded the **** out of my E-MU 1212m. OPAMP, Cappies n all. Added bypassing caps and reservoir caps.

I replaced the bottom two DUAL JRC 2068 OPAMPs that correspond to the balanced line outputs.

I first tried to install the TI THS6042 DSL Line driver Dual OPAMP. The output gave too much white noise and distorted when I installed these. I figured these may not be the optimal choice, so I popped in two AD8620s. They worked for 10 minutes, gave interminnent distortion, and finally died on me.

Then, as a last resort, knowing that BB OPA2228 will work no matter what voltage constrains the card might have to throw at it, i put the OPA2228u variant on the E-MU, and though the result is way better than the stock card, but not as good as I heard when the AD8620s were installed and working.

Can somebody help me figure out why the AD8620s died? Is it because of overvoltage? What are the voltage requirements for the OPAMPs on the E-MU 1212M?

I read the datasheet of the JRC2068 and it says +/- 18v as the power rating of the OPAMP. Is it using +/- 16v on the card? In that case what OPAMPs can I use from TI's or AD's portofolio, because that is all I can find in India.

Any other OPAMPs that work well will also be welcome. If anybody can help me by shipping them to India (i will pay via PayPal) that will be great too.

 

[Iron_Dreamer]

I don't think it is overvoltage, every soundcard that I've modded so far used +/-12v for the opamps' power. I used the LT1364, very high speed, which didn't work at all without .01uF polypropylene bypass caps from the voltage rails to ground. Put them in, and voila! perfect sound. You might need to try this. Which of the caps did you replace on the two boards? Have any way to post pics, that might help in troubleshooting. Congrats on having the guts to mod your card

 

[nutrax]

Hi Iron Dreamer,

I in fact looked at the LT1364 datasheet to choose the closest equivalent on TI's Side, which turned out to be the THS6042.

I modded all caps I could see clearly attached to the board in your mod-thread photos. Didn't dare go further to find out which others could be replaced.

My card has been working perfectly fine with the OPA2228Us for the past five days now, so I guess the caps are alright. Just can't figure out why the AD8620s died.

BTW, It would be really helpful if could you please post a clearer picture from a few more angles on bypass and decoupling caps around the OPAMPs. That area was far too complex to decipher in your photos.

I can even offer you hosting for the high-res photos of your 1212m modification project if you want. I manage two high-bandwidth dedicated servers in the US.

PS: could you please send me two LT1364s? I will paypal ASAP.

 

[nutrax]

Okay! Here is something that seems highly interesting.

Seems TI came out with a new DAC yesterday, the PCM1792

http://focus.ti.com/docs/prod/folder...t/pcm1792.html

132dB Maximum Dynamic Range, 127dB Minmum. And what's even better is that it is available in the same form factor as the CS4398, the DAC onboard the E-MU. It isn't pin compatible, so it will require significant amount of "ultra careful" rework to put it into the E-MU... but it is possible cause I have done similar work on my CDP...but the CDP was 50 dollars....I just dont have the guts to do it on the E-MU...

nebody with guts of steel and an E-MU to spare? And I want an answer to my last question as well...

 

[Iron_Dreamer]

Somehow I didn't notice your first reply to my post. I don't have any LT1364's sitting around, or I would send you some. They're only $7 on digikey. I would post some more pics, I just don't know if the camera I have is capable of taking any better pictures. I have quite a bit of free web hosting from my Univ, so that's not a problem. Quite honestly, I put up those pics expecting people to ooh and ahh, not really to try and decipher every last mod I did, so I wasn't so concerned with whether every last detail was viewable.

The decoupling caps need only to be attached to the voltage rails of the opamp (pins 4 and 8) then to a ground. Biasing resistors go from the v- rail to the outputs, pins 7 and 3. Pretty simple, really. Everything else I changed just sits in the original position for each capacitor, aside from the polys that I attached to some of the SMD decoupling caps around the DAC chip.

That new TI DAC chip looks interesting, for sure, however, the pins aren't the only thing to worry about. It is quite likely since it is by a different company that the logic programming would be different, which means that it wouldn't work even if we got the pins right somehow. Too much of a PITA for me anyway, especially since I have found the RME HDSP 9632 to sound better than the E-MU anyway, that I where I'll be going.