USB Audio-DAC

This circuit is pre-eminently suitable for PCs and laptops that are not equipped with a built-in sound card but do have a USB interface. However, the ‘mini PC sound card’ can also be useful for other applications and various experiments.The introduction above provides a nearly complete character outline for the circuit under consideration. In brief, it is a 16-bit stereo version of a digital to analogue converter with USB interface. The converter may be used for a range of audio applications. But the first thing that comes to mind is an external sound card for PCs and laptops without such a card, or as an expansion card in the event a second one is desired.The circuit is conspicuously compact and simple by design, because it consists mainly of an integrated D/A-converter supplemented by two opamps. This simplicity however, does not imply that the quality of this ‘USB audio-DAC’ has been compromised. On the contrary, we would like to say.

Resistors:
R1 = 1kΩ5
R2,R3,R4 = 22Ω
R5 = 1MΩ
R6 = 470Ω
R7 = 680Ω
R8,R9,R13,R14 = 10kΩ0 1%
R10,R15 = 8kΩ25 1%
R11,R16 = 100Ω
R12,R17 = 220kΩ
Capacitors:
C1,C6,C10,C20 = 10µF 63V radial
C2,C5,C7,C8,C9,C11,C19,C21 = 100nF ceramic, lead pitch 5mm
C3,C4 = 18pF
C12,C15 = 1nF5 1% polystyrene/polypropylene
C13,C16 = 270pF 1% polystyrene/polypropylene
C14,C17 = 3µF3 MKT (Siemens), lead pitch 5 or 7.5mm
C18 = 470nF, lead pitch 5mm
C22 = 470µF 25V radial
C23-C26 = 22nF ceramic, lead pitch 5mm
Semiconductors:
D1,D2 = 1N4148
D3 = green high-efficiency LED
D4 = red high-efficiency LED
B1 = B80C1500 (80V piv, 1.5A peak), round case
T1,T2 = BC557B
IC1 = PCM2702E (SSOP-28 case) (Burr-Brown)
IC2 = OPA2353UA (SO-8 case) (Burr-Brown)
IC3 = 78L05
Miscellaneous:
K1 = USB connector, receptacle style B (PCB mount)
X1 = 12MHz quartz crystal
PCB, order code 000169-1