I am looking for a device(chip or finished product) that can take a stereo audio signal(any level) and present it to a PC via USB AND be DC coupled(in the audio path). Am familiar with the TI PCM2902 used in the Behringer uca202, but it is AC coupled inside the chip(-3db at 4 Hz). I modified it for DC in its analog path but found it was not suitable. Does anyone know of a codec with a USB audio interface that goes down to DC?
I think that you need to be looking either at very expensive, very cheap, or modifying.
Audio interfaces should not be DC coupled. DC is not sound, it’s wind.
You may find that some very cheap audio devices have DC coupling for the sake of frequency response without the expensive of good quality input capacitors. For high quality A/D conversion down to DC your are looking at instrumentation converters which are likely to be very pricey. The third alternative is modification, as you did with the Behringer. Why was the Behringer not suitable?
Thanks for your reply.
Actual application is signal processing from a specialized piece of hardware(not audio). It has to do with corona discharges and the “hardware” has a DC component. The Behringer uses a Texas Instruments PCM2902 which is natively AC coupled. I was able to modify the input circuit such that the op-amp output to the ADC is DC coupled. However, internal to the above chip is a digital high pass filter that limits the low end to about 3.7 Hz. Thus I continue my quest.
Some time in the twelfth century, somebody posted a process whereby you could modify a standard SoundBlaster PC sound card to pass DC. The project was a very large screen voltmeter.
Google your brains out.