[Glassman]

Quote:

Originally posted by Wodgy Glassman, you have a very poor understanding about this stuff. The AD1852 uses an 8x oversampling digital filter. The ultrasonic noise floor is flat to -120dB all the way up to 176.4 kHz, at which point you get noise from the sigma-delta modulator. This is so far from the audio band that it really doesn't matter.

you're completely right, the stop band is somewhere above 300kHz, after that it doesn't mater.. Analog has really nice digital filter.. Crystal is not that good I believe, Ti neither.. they all state stopband at ~0.65fs, fs being incoming sample rate, not oversampled as it seems to me from datasheets

edit: it's not flat to 176.4kHz.. 8x oversampling means 352.8kHz, which is a total bandwidth where the filter can act.. and it acts from ~22kHz to ~330kHz, which is a stop band with -110dB

 

[Iron_Dreamer]

Doing this mod to Slipkid's card today, I realized that the output opamp must be removed for the mod to work correctly.

 

[Edwood]

You have to remove that adapter now?

Oh boy. Guess I should return those OP627 and LT1122's I just got from Digikey......

-Ed

 

[Iron_Dreamer]

No, although in trying some different stuff, I did end up removing it. The adapter doesn't make a difference, only the opamps need to be taken out of it. Or in the case of his card, I had to remove the stock opamp in order for it to work properly.

 

[Edwood]

Ah, so I can just yank my OPamp, and leave the adapter there?

-Ed

 

[Iron_Dreamer]

Quote:

Originally posted by Edwood Ah, so I can just yank my OPamp, and leave the adapter there? -Ed

Bingo. And if you perfer the opamp sound to the completely bypassed sound, it is very easy to remove the caps, so no biggie.

 

[Edwood]

Well, we do have more than one RME PAD to compare so we'll know for sure.....

-Ed

 

[Glassman]

you can compare one card with bypassed analog stage and another with removed smt caps, which form low pass filter.. I'm curious, becouse I believe it's the filter which sounds bad, not the summing opamp..

 

[Iron_Dreamer]

I tried removing the stuff other than the opamps from my card, and it didn't go very well, so I am done screwing around with it, since I am happy with the current sound.

 

[Edwood]

LOL, when has that stopped you from modding it further.

-Ed

 

[Wodgy]

You can't just remove caps randomly -- you need to trace the output stage and figure out its layout. (i.e. It would suck if you accidentally removed some of the power supply filtering caps that benefit the DAC too.)

 

[Iron_Dreamer]

Quote:

Originally posted by Wodgy You can't just remove caps randomly -- you need to trace the output stage and figure out its layout. (i.e. It would suck if you accidentally removed some of the power supply filtering caps that benefit the DAC too.)

I guess I should ahve been more specific, I did do what you describe, followed the path from the DAC to opamps, and removed 4 sets of the of same parts, 4 resistors and 2 capacitors per output line, and bridged the route to the opamp with solder. However it was a major PITA to get the pads connected properly, and I eventually just got sick of screwing with it. I have one more idea I may try when I get bored some day.

 

[Glassman]

you were supposed to remove JUST the caps, not the resistors, 'coz signal flows through them.. no wonder it didn't work

if you remember which resistor belongs where, try to get them back..

 

[Iron_Dreamer]

Quote:

Originally posted by Glassman you were supposed to remove JUST the caps, not the resistors, 'coz signal flows through them.. no wonder it didn't work if you remember which resistor belongs where, try to get them back..

Most of them didn't survive being removed. What I was going for was DAC -> opamp -> ouutput jack, by removing all the other parts and soldering paths from the DAC to the opamps. It didn;t go according to plan, so I have one more idea left, before I settle on the card in its' current form, until I buy an external DAC (god knows when).

 

[Edwood]

Buy this one.

-Ed