Cheap C-Media (?) sound card

This USB sound card that presents itself as C-Media is one of the cheapest sound cards available, usually in the price range $1-2. I've tested it for a short time.







USB descriptor dump:

VID=0x0D8C PID=0x000C
Product string: C-Media USB Headphone Set
Audio Device Class + HID (composite device) 
  

Few notes:

  Crystal frequency: 12 MHz.
  100uF/10V capacitors are separing headphone output.
  Audio input: mono. Two "live" contacts of mic jack are shorten together.
  Noise with nothing attached to input: ~30 LSB (surprising low).
  AGC setting (only one available in adv settings) works like a mic boost rather while gain control
  for recording seems to have no effect.
  

In a short time I wasn't able to find any point on PCB that would allow DC voltage sampling - it's possible that this card is not a good candidate for PC oscilloscope.


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