JEDAC - yet another take on a DIY high-end USB Audio DAC

If you are wondering what an Audio DAC is, this might not be the project
page you are looking for.
But for short, a DAC (Digital-Analog Converter) is
a computer soundcard, in this case intended to give the maximal (audiophile)
audio quality in terms of reconstruction accuracy, signal/noise level and
channel separation.
Text, images and downloadables copyright (c) 2013
Jan-Erik Skata. Schematic and PCB design is freely available for
non-commercial/hobbyist use.
For contacting me, username at topdomain (just
to avoid spam).

Background
Having previously built a simple USB DAC with PCM2705,
I was surprised by the improvement in sound quality over the motherboard sound
output.

I decided to go full out and build a more ambitious DAC using
PCM2707 (PCM2705 is NRND and the TQFP32 of PCM2707 is better to hand solder
compared to SSOP28).
This will also be entirely USB powered, like it or
not.

While designing my DAC I have had a lot of reference from PupDAC,
thanks for putting up your schematics! I will further refer to the sections that
are utilized in my design.

In short:

Texas Instruments PCM2707C
for USB Audio interface and I2S to DAC.

Texas Instruments PCM1794A
for D/A conversion. This may be the best specced audio DAC on the market
today.

Texas Instruments OPA4134
for output signal conversion and buffering. This is one of the best regarded
audio opamps on the market. Same footprint as TL074 et al.
Thus, entire
audio chain is Burr-Brown heritage.

Texas Instruments TPS60501
and LM2662 inductorless
switch-mode powersupplies for 3.3V and -5V.

Largest differences from
PupDAC in design specification are:

Single sided PCB, suitable for toner transfer, albeit for a few vias and
jumpwires.

All passives hole-mount.

Normal crystal instead of a fancy oscillator module.

Four identical RCA line outs (+ pads for chassis mount 3.5mm stereo jack) of
which two are buffered, since I have had enough from splitter cables.

+-5V to output opamp instead of +-2.5V for more headroom, simplicity of
design and larger selection of opamps.

No intention of functioning as a headphone amplifier, thus the output level
will be closer to line level (0.316 Vrms for consumer audio, 1.228 Vrms for
professional audio).

Largest improvements over simple PCM270x
internal DAC:

Vastly superior conversion quality from PCM1794.

Higher quality output stage with double supply voltages, more headroom and
high-end opamp.

No capacitors in the signal route.

Much lower (resistive) output impedance.

Drawbacks and known
issues:

Hardware volume control of PCM2707 does not work with I2S output, need to
use software. In Windows, this requires no action. In Linux/ALSA, need to
configure softvol, my /etc/asound.conf in download section.

Single sided board can never be considered truely high-end.

Circuit description

Entire
circuit

USB
audio section with PCM2707
I realize the PCM2707 could be fed 3.3V
externally and that could be an idea since it is already generated onboard, but
it also has an internal regulator and only needs a capacitor to ground.
Otherwise this is according to datasheet.
Note C15 is a crystal, not a
capacitor. KiCAD did not have the symbol.

PCM1794 DAC and
TPS60501 regulator section
Again, this is like in the datasheet. R2 is
not a resistor but a jumper for selecting sharp or slow (default, open, as on
PupDAC) filter rolloff. Decided to use separate capacitors on VCOML/R as in the
datasheet even though PupDAC uses only one.
TPS60501 is a charge pump voltage
regulator that feeds 3.3V to PCM1794.

Analog
stage
Similar to PupDAC but with lower gain (R18, R19, R20, R21). This
approach is somewhat different than TI's solution with I/U buffers, and there
are many opinions which is better. Output is also buffered for two of the
outputs, to make use of all four amplifiers in the chip.

LM2662
section
Charge pump voltage inverter, creates -5V from 5V, necessary for
the output opamp. Here again, R22 is a jumper and not a resistor. If open, the
switching frequency will be 20 kHz. If closed, the frequency will be 150 kHz but
the efficiency will be lower. Your choice, I hear no problem at 20 kHz.

BOM and component values
U1: TPS60501
U2: PCM2707C
U3:
PCM1794A
U4: OPA4134, TL074 or similar op-amp
U5: LM2662

R1, R3,
R9: 10k
R2, R22: jumper (open)
R4, R7: 1k5
R8: 1M
R5, R6, R10, R11,
R12, R13: 22R
R14, R15, R16, R17: 100R
R18, R19, R20, R21: 820R
R23,
R24, R25, R26, R27, R28, R29, R30: 100R

C1: 4u7 elko
C2, C5, C6, C7:
1u polyester
C3, C10, C12, C14: 10u elko
C8, C9: 47u elko (- on pin, + on
+5V)
C4, C11, C13, C21, C22, C23: 150n polyester
C15: 12 MHz crystal -
used cap for simplicity in KiCAD
C16, C17: 4p7 (dependent on xtal
capacitance, up to 33pF)
C18, C19: 220p ceramic
C21, C24: 47u elko
low-ESR

USB connectors: used http://dx.com/p/diy-mini-usb-5-pin-female-90-degree-dip-socket-connector-silver-10-piece-pack-127646

RCA connectors: used http://dx.com/p/dual-sockets-3-5mm-av-jack-connectors-red-black-silver-10-pack-122545

PCB design

PCB design screenshot from KiCad.
Please review the design in KiCad
(2013-may-18)-stable, picture only for illustrational purpose.
Layer B.Cu
(green) are jump wires.
Filled area (ground potential) has been left out for
clarity.
NOTE: Design has to be printed mirrored for toner transfer. Please
ensure you get it right.

Construction

Designed
the PCB to fit in a smallish box (WCA-H2853).

Toner transfer done with good results.

Board
etched and even the finest traces are intact.

First
surface mount components soldered; regulators that give 3.3V to DAC and -5V to
opamp.

All the necessary
components soldered and plugged in for a first test - and it works!
Lesson of
the day; electrolytic capacitors are bigger than you think.

All the
surface mount chips soldered.

Preparing
the box.

Board
assembly completed with RCA jacks.

Finished
DAC with four identical outputs and Mini-USB input.

Downloads
Schematic
and PCB design in KiCad format.
Linux/ALSA
/etc/asound.conf with softvol configured.