AC coupling in sound cards

[mogwai]

hi all!

I am wondering if there is any way to bypass the AC coupling capacitors at the output of a soundblaster PC card. I need to use the DAC to export some waveforms with dc offset which cannot be done due to protective AC coupling capacitors in all sound cards.

Moreover, anyone has service or schematics for an old 16bit Soundblaster (model CT4520) ?

Thanks in advance.
mogwai.

 

[flatulent]

their own dc offset

This may not work if the sound card has its own DC offset. You may be better off making an op amp circuit that allows you to manually set the DC offset and add this to the AC signals out of the sound card.

 

[artem]

It would be better to chekc lowest pass frequency , as if your output operates below this freq - output will not be correct . Most probably it is set by decouploing capasitor within sound card .

 

[flatulent]

DAC

If you can identify the DAC circuit on this card (which may include an op amp external to the DAC) you can tap off the signal before any AC coupling is done and eliminate all of the problems described in the previous posts.

 

[mogwai]

Thank you for your quick replies

Most probably I will try to identify connection points to bypass the capacitors.

Thanks again.
mog.

 

[arturt134]

Bypassing AC coupling capacitor may have no effect. If this card have sigma-delta AD converter, with digital high pass filter (like PCM1800 from Texas Instruments), all DC offset will be withdrawn.