W-DAC XLR – Very High Performance Compact Balanced Audio DA-Converter

The design is based on W-DAC v2 where the output stage is replaced with a fully differential output stage. This board will replace the W-DAC v2 and the XLR add-on.

Excellent performance, typical:
- THD+N ratio: -116 dB (997 Hz -1 dBFS)
- THD ratio: -122 dB (997 Hz, -1 dBFS)
- Dynamic range / SNR: 122 dBA
- Crosstalk: < -130 dB, 10 kHz
Balanced XLR output, 4 Vrms output level
- Can be adjusted by adding/changing resistors
DC-coupled output path (no DC-blocking capacitors in audio path)
- DC-offset typically up to 3mV but can be up to 5mV; see notes in the measurements tab
AK4493SEQ DAC, LM4562 and OPA1632 opamps, LT3042 regulators, thin film resistors and C0G capacitors in audio path
Compact 85 mm x 50 mm 4-layer PCB
PCM up to 32 bits and 768 kHz sample rate
I2C-version supports DSD up to DSD512
Selectable digital filter (via jumper link in HW-version, via registers in I2C-version)
Hardware output mute with relay (automatic, can also be manually muted)

Requires following supplies (indicated max current):

5V for digital (35 mA)
+/- 12-15V (55 mA per supply) for opamps
6V for DAC references and analog supplies (40 mA)
- This can also be taken from +15V (connecting outside the board or soldering ferrite beads or 0R on board; this increases VP current to 75mA)
All supplies provided via one 6-pin Molex Micro-Fit for easy interfacing with our power supplies

Features

Common features for both HW- and I2C-variant:

Identical performance
Hardware output mute
- Automatic supply monitoring reduces loud pops at start-up and power-down when connected directly to a power amplifier
- External mute input can be used to engage mute from an external source (e.g. from DAR 18 S/PDIF receiver)

HW-variant features

Easy to use, no microcontroller needed
Digital filter selection with jumper link

I2C-variant features

Needs an I2C-host, for example microcontroller
Digital filter and all other settings, including digital volume control, done via registers
DSD-support
We do not provide a control firmware but there are very simple example writes in the W-DAC XLR guide

Important information on order

All SMD components are soldered down and the board is fully tested, connectors and headers are soldered if selected.
Please ensure you have the skills to solder the remaining components and wires to connect the board in your system – and most of all understand what you are doing. Especially pay attention you have the correct power supplies and signal levels.
Be careful with supply polarity and level, incorrect connections may damage the board and/or your power supply.
If you need help prior to purchase, please contact us.

Order contents

By default, connectors and headers are delivered unsoldered.

HW-version:

Fully tested board with all SMD components populated
6-pin Molex power connector
2×5 male pinheader + one jumper link for digital filter selection
1×2 male pinheaded for EMUTE input

I2C-version:

Fully tested board with all SMD components populated
6-pin Molex power connector
2×2 male pinheader for I2C and IRQ
1×2 male pinheaded for EMUTE input
3pcs 0R resistors for changing I2C-address

Changes from W-DAC v2

W-DAC XLR is based on W-DAC v2 which was used as a starting point for the design – and most parts of the PCB remain identical. Some changes to mention:

More symmetric and simplified fully balanced output path gains small performance improvement – and reduced cost and complexity compared to W-DAC + XLR add-on.
Power supply inputs have added protection components.
Due to these changes and removal of the edge headers (where W-DAC v2 XLR add-on stacks onto), the PCB layout around the supply input and output stage has changed quite significantly.
I2C-version does not have the attenuation relays the W-DAC v2 I2C has.
- There are placeholders on the PCB but these were removed last minute because they did not add enough improvement anymore. It would improve DR a few dB when engaged but the extra loading deteriorated THD slightly in this circuit.
Lots of small changes throughout the board.

The functionality of the board remains the same. Measured performance is slightly better than W-DAC v2, mainly due to one less opamp stage compared to the W-DAC v2 + XLR add-on. The new board is 15mm longer due to XLRs.

More information

For more information on using the board, see W-DAC XLR guide. There is also a post on how to connect DAR 18 and W-DAC. As this XLR-version is functionally identical to the W-DAC v2, these instructions apply despite being written for the W-DAC v2.

For measurement results and version history, see the tab above.

There is also a video showing the board, its features, and how it is connected to other boards:

Files

Control	HW, I2C

Measurements and Version History

See board version history at the bottom of the page.

Measurement results

Below are example measurements when evaluating W-DAC XLR v1.1 boards. Note that the results are stated as typical, meaning we do not guarantee a certain level of performance for practical reasons. That being said, all test boards measured showed very consistent performance (usually within +/-1dB of the stated typical THD+N - some better than the typical) and this is what we aim for with the design.

THD+N

THD+N vs. Amplitude, 997Hz, 20kHz bandwidth.

THD vs. Amplitude, 997Hz, 20kHz bandwidth.

THD+N vs. Frequency, -1dBFS, 20kHz bandwidth.

THD vs. Frequency, -1dBFS, 20kHz bandwidth.

THD+N vs. frequency within 20kHz BW doesn't show high frequency harmonics but it shows THD+N doesn't increase at low frequencies.

Dynamic range

Dynamic range is consistently slightly above 122dB A-weighted.

Crosstalk

Crosstalk is consistently better than -130dB at 10kHz.

FFT

FFT spikes around 50kHz are the image frequencies as sample rate is 48kHz. This was measured with no digital filter jumper link, therefore LD Sharp filter.

FFT 256K, 997Hz, -1dBFS, 192kHz sample rate.

FFT 256K, 997Hz, -3dBFS, 192kHz sample rate.

Frequency response

Output filter is 3rd order Bessel type for great phase behaviour, with corner frequency around 100kHz to get good attenuation for oversampling images. Attenuation at 20kHz is around 0.2dB. The output stage is DC-coupled and goes all the way down to 0Hz.

Note that although the filter fc is around 100kHz, the DAC itself rolls off as well and the overall -3dB point is around 70kHz.

DC-offset

DC-offset is slightly higher, up to 5mV. This is a combination of the DAC IC offset and the output stage offset as the design is DC-coupled - no DC-blocking capacitors in the signal path.

Normally this is not a problem in any application but it is worth keeping in mind if the W-DAC is connected directly to a high-gain power amplifier without preamplifier in between, and especially if the connected speakers are very sensitive.

The mute relay at the W-DAC output prevents large pops caused by supplies but this mute itself may cause a small pop with the inherent DC-offset, which may be amplified to an audible level by a high-gain amplifier and/or very sensitive speakers. In such case, the final pop should be controlled by the power amplifier mute.

Board version history

Version 1.1, current version. First boards sold were v1.0 but it is practically identical.

The design is based on W-DAC v2.1 which was used as a starting point, major part of the PCB being identical. The output stage basically combines W-DAC XLR addon in the W-DAC design. The board was made longer to accommodate the XLR-connectors.

W-DAC XLR – Very High Performance Compact Balanced Audio DA-Converter