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USB Audio Codec with S/PDIF

record digital audio with your PC

Published in issue 316, December 2002

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.

Components

Resistors:
R1,R3 = 6kΩ49
R2,R4 = 3kΩ92
R5 = 4-way 1kΩ5 SIL array
R6,R7 = 22Ω
R8 = 1MΩ
R9,R16 = 5kΩ76
R10,R17 = 6kΩ81
R11,R18 = 6kΩ65
R12,R19 = 20kΩ0
R13,R20 = 10kΩ0
R14,R21 = 100Ω
R15,R22,R25 = 100kΩ
R23 = 4Ω7
R24 = 8kΩ2
R26 = 33kΩ
R27 = 1kΩ5
Capacitors:
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
Semiconductors:
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)
Miscellaneous:
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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