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USB Audio Codec with S/PDIF

record digital audio with your PC

USB Audio Codec with S/PDIF
The USB Audio-DAC described exactly two years ago received unexpected acclaim as a small external sound card. Soon after the publication we received an number of requests for a similar circuit, but then capable of recording via the USB port. The codec presented in this article does just that, and more, while not a much more elaborate circuit than the Audio-DAC.The circuit described in this article is built around a ‘stereo audio codec’ IC type PCM2902 from Texas Instruments/Burr-Brown. Clearly, this chip is from the same family as the PCM2702 we used in the USB Audio-DAC. However, it is also an upgrade because besides the features of the 2702 (analogue stereo output, USB interface) it also sports an analogue stereo output and an S/PDIF input and output. The latter even allow digital recordings to be made to and from the PC. One proviso should be mentioned, however.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Component list
R1,R3 = 6k?49
R2,R4 = 3k?92
R5 = 4-way 1k?5 SIL array
R6,R7 = 22?
R8 = 1M?
R9,R16 = 5k?76
R10,R17 = 6k?81
R11,R18 = 6k?65
R12,R19 = 20k?0
R13,R20 = 10k?0
R14,R21 = 100?
R15,R22,R25 = 100k?
R23 = 4?7
R24 = 8k?2
R26 = 33k?
R27 = 1k?5
C1,C2,C14,C21 = 3µF3 50V, MKT (Siemens), lead pitch 5 or 7.5mm
C3,C4 = 22pF
C5,C12,C13 = 10µF 63V radial
C6,C23,C24,C28 = 100nF ceramic, lead pitch 5mm
C7,C8 = 33pF
C9,C16 = 1nF5 1% *
C10,C17 = 1nF 1% *
C11,C18 = 470pF 1% *
C15,C22 = 47pF
C19,C20,C25,C26 = 1µF 25V, SMD case 0805 (e.g., Farnell # 317-640)
C27 = 100µF 10V radial
*) polypropylene or polystyrene (EMZ) Inductors:
L1,L2 = BLM31A601S, SMD case 1206 (e.g., Farnell #. 581-094)
L3,L4 = 47µH
D1 = LED, red, high efficiency
T1 = BC557B
IC1 = PCM2902 (Texas Instruments/Burr-Brown)
IC2 = OPA2353UA (Texas Instruments/Burr-Brown)
IC3 = TORX173 (Toshiba)
IC4 = TOTX173 (Toshiba)
IC5 = LE33CZ (ST) (e.g., Farnell # 302-4568)
JP1,JP2 = 3-way SIL pinheader with jumper
JP3,JP4,JP5 = 2-way SIL pinheader
K1,K2 = 3.5mm stereo jack socket, PCB mount (Conrad Electronics # 73 28 93-88)
K3 = USB connector, PCB mount, type B
X1 = 12 MHz quartz crystal, parallel resonance, (Cload = 30pF)
PCB, order code 020178-1
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