Mini Audio DAC

Schematic Diagrams      Comments Off on Mini Audio DAC

In past we described an
S/PDIF tester, consisting of a special decoder IC with integrated D/A
converter. Two implementations of the ‘IEC 60958 audio DAC’ from Philips
could be used here: the UDA1350ATS or the UDA1351TS. The latter has a
frequency range up to 96 kHz. However, a number of readers were
disappointed that this circuit was not accompanied by a PCB design. That is the reason that we present a similar ‘Mini Audio DAC’ here, this time with matching PCB
layout. The IC that has been used here, the UDA1351H, belongs to the
same family as the aforementioned types, but is packaged in a different
housing. The advantage of the SOT307-2 (QFP44) package is that the pins
are a little further apart (0.8 mm instead of 0.65 mm), which makes
soldering with a normal soldering iron considerably easier.

The single sided PCB has been made as
compact as possible and is fitted with components on both sides. The
majority of components are on the actual component side, but six ceramic
SDM capacitors have been placed on the copper
side close to the IC, to obtain optimum decoupling. The are also three
decoupling inductors in SMD packages, which are also on the solder side for the same reason. Including the cinch-connector the PCB
is not larger than 51?37 mm. For short duration use, two AA batteries
may be used as power supply, but at 44 kHz the circuit draws a current
of 22mA and at 96 kHz, 33mA, which is a little bit too much for a
battery power supply.

D1 indicates that a usable input signal has been detected. R3 and R4
ensure that output electrolytics C4 and C5 are charged even when no
load is present, while R5 and R6 are the usual limiting resistors for
capacitive loads. The output consists of three PCB pins, so that you can, depending on the application, fit cinch (RCA)
chassis connectors or a jack to connect a headphone. For a detailed
description of the IC we refer you the article mentioned above and the
datasheet for the UDA1351H. We conclude by listing the specifications,
measured at a power supply voltage of 3V. The graph shows the amplitude
characteristic, measured with a test CD. As can be seen, the attenuation
is only about 0.5 dB at 20 kHz!

Resistors:
R1 = 75Ω
R2 = 1kΩ
R3,R4 = 10kΩ
R5,R6 = 100Ω
R7 = 1Ω

Capacitors:
C1 = 180pF
C2 = 10nF ceramic, lead pitch 5mm
C3 = 100nF ceramic, lead pitch 5mm
C6,C8,C10,C12,C14,C16 = 100nF, SMD shape 1206
C4,C5 = 47µF 25V radial
C7 = 10µF 63V radial
C9,C11,C13,C15,C17,C18 = 100µF 25V radial

Inductors:
L1,L2,L3 = Murata BLM31AJ601SN1L

Semiconductors:
D1 = high-efficiency LED, dia. 3mm
IC1 = UDA1351H (Philips)

Miscellaneous:
K1 = cinch (RCA) socket, PCB mount, e.g., Monarch T-709G