Cheap C-Media (?) sound card
This USB sound card that presents itself as C-Media is one of the cheapest sound cards available with price $1.1-$2 depending on vendor.
Device markings: HX2010-0705, production date 40th week of 2013 (or later?).
Device enumerates as composite device: sound card + HID input. HID input part is used for audio volume and mute control and it functionality is slightly broken – same as with multimedia keyboard it controls default sound card settings, not necessary settings for this specific device.
USB descriptor dump:
VID=0x0D8C PID=0x000C Product string: C-Media USB Headphone Set Audio Device Class + HID (composite device)
Judging by the descriptors chip inside is identical as in previously described “C-Media” sound card version without any control keys.
Unlike the previous “C-Media” USB sound card I’ve tested and similar card from this thread it was easy to find point where DC signal component is not blocked:
- according to device properties reported by Win7 it offers 44100 and 48000 Hz sampling
- there is 2.23V voltage (DC offset for ADC) on the C6; output impedance of this offset source is relatively high – short-circuit current is 20uA; adding 120k resistor in series reduces it to 8uA
- resistor in series (I’ve used 120k and software is calibrated for it by default) seems like the cheapest way to extend measured voltage range to 0-6V; noise measured in this configuration = 20mVpp
- make sure to disable AGC and set fixed volume (by default plugin is calibrated for Volume = 0) for sound input associated with card (Win7 below):
For more detail: Cheap C-Media (?) sound card